Difference between revisions of "Detailed DC system design"

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[[Category:Design examples]]
 
[[Category:Design examples]]
−
Design will be completed in January 2021
 
−
 
 
<big><big>[[Physical evaluation]]</big></big>
 
<big><big>[[Physical evaluation]]</big></big>
  
 
'''Location:''' Pampachiri, Apurimac, Peru<br />
 
'''Location:''' Pampachiri, Apurimac, Peru<br />
−
'''GPS coordinates:'''  14°11'37.65"S  73°32'31.73"W<br />
+
'''GPS coordinates:'''  -14.1870656, -73.5445298<br />
−
'''Altitude:''' 3378m<br />
+
'''Altitude:''' 3378 m<br />
−
'''Description:''' A two story adobe home in the Peruvian Andes with only DC power needs. <br />
+
'''Description:''' A two story adobe home in the Peruvian Andes with only DC power needs. The home is used all year and the loads are used consistently throughout the year. Load usage is primarily during the evening/night. The homeowners do not intend on adding any major appliances in the near future.<br />
  
 
<gallery widths=250px>
 
<gallery widths=250px>
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|-
 
|-
 
|1
 
|1
−
|5 W LED
+
|LED light
 
|6
 
|6
 
|5 W
 
|5 W
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|2
 
|2
 
|Radio
 
|Radio
 +
|1
 
|6 W
 
|6 W
−
|1
 
 
|6 W
 
|6 W
 
|1
 
|1
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|3
 
|3
 
|Cell phone
 
|Cell phone
 +
|2
 
|10 W
 
|10 W
−
|2
+
|20 W
−
|29 W
 
 
|1
 
|1
 
|1 hours
 
|1 hours
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|}
 
|}
 
*'''Month:''' The month of the year.
 
*'''Month:''' The month of the year.
−
*'''Average monthly insolation:''' Solar resource data obtained for the location from [[Weather and solar resource data sources]].
+
*'''Average monthly insolation:''' Solar resource data obtained for the location from [[Weather and solar resource evaluation]].
 
*'''[[Load evaluation#Total average daily energy demand|Total average daily energy demand]]''' for the month from the load evaluation.
 
*'''[[Load evaluation#Total average daily energy demand|Total average daily energy demand]]''' for the month from the load evaluation.
 
*'''Ratio =''' Total average daily energy demand ÷ Average monthly insolation
 
*'''Ratio =''' Total average daily energy demand ÷ Average monthly insolation
Line 232: Line 230:
  
 
==[[:Category:Design parameters|Design parameters]]==
 
==[[:Category:Design parameters|Design parameters]]==
−
'''[[System voltage parameter]] =''' 12 V
+
'''[[DC system voltage]] =''' 12 V
 
*The system, based upon the load evaluation, will be relatively small. A 12 V system makes the most sense.
 
*The system, based upon the load evaluation, will be relatively small. A 12 V system makes the most sense.
 
'''[[Irradiance safety parameter]] =''' 1.25
 
'''[[Irradiance safety parameter]] =''' 1.25
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==[[Energy storage sizing and selection]]==
 
==[[Energy storage sizing and selection]]==
 
'''Step 1: Determine depth of discharge parameter'''<br />
 
'''Step 1: Determine depth of discharge parameter'''<br />
−
For this project a depth of discharge of .5 (40%) is a good compromise.
+
For this project a depth of discharge of .4 (40%) is a good compromise.
−
*Depth of discharge = .5
+
*Depth of discharge = .4
  
 
'''Step 2: Determine days of autonomy parameter'''<br />
 
'''Step 2: Determine days of autonomy parameter'''<br />
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{| class="wikitable" border=1 style="width: 80%;"
 
{| class="wikitable" border=1 style="width: 80%;"
 
! style="width: 20%"|Total Ah required
 
! style="width: 20%"|Total Ah required
−
! style="text-align:left;"| = Average daily Watt-hours required ÷ System voltage parameter × Battery temperature correction factor (step 3) × Days of autonomy parameter (Step 2) ÷ Depth of discharge parameter (Step 1)
+
! style="text-align:left;"| = Average daily Watt-hours required ÷ [[DC system voltage]] × Battery temperature correction factor (Step 3) × Days of autonomy parameter (Step 2) ÷ Depth of discharge parameter (Step 1)
 
|-
 
|-
 
|
 
|
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|}
 
|}
  
−
'''Step 5: Calculate number of batteries in series'''<br />
+
One MK Deka 12V 55 Ah AGM battery will provide enough storage capacity. [http://www.opensourcesolar.org/w/downloads/specsheets/8A22NF-DEKA_Spec_Sheet.pdf Specifications sheet]
−
A 12 V battery is ideal for a system of this size.
+
 
 +
:Specifications:
 +
:*Battery type: AGM
 +
:*Nominal voltage: 12 V
 +
:*C/20 rated capacity: 55 Ah
 +
 
 +
'''Step 5: Calculate number of batteries in series'''<br />  
 
{| class="wikitable" border=1 style="width: 80%;"
 
{| class="wikitable" border=1 style="width: 80%;"
 
! style="width: 20%"|Batteries in series
 
! style="width: 20%"|Batteries in series
−
! style="text-align:left;"| = System voltage parameter ÷ Chosen battery voltage
+
! style="text-align:left;"| = [[DC system voltage]] ÷ Chosen battery voltage
 
|-
 
|-
 
|
 
|
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|-
 
|-
 
|
 
|
−
| style="text-align:left;"| = 1 × 12 V battery is sufficient
+
| style="text-align:left;"| = 1 battery
 
|}
 
|}
  
−
'''Step 6: Calculate number of batteries in parallel'''<br />
+
'''Step 6: Calculate number of parallel battery circuits'''<br />
−
In Peru 12 V AGM batteries are widely available in 40 Ah, 55 Ah and 75 Ah sizes. 55 Ah is too small, so a 75 Ah battery will have to be used.
+
 
 
{| class="wikitable" border=1 style="width: 80%;"
 
{| class="wikitable" border=1 style="width: 80%;"
−
! style="width: 20%"|Batteries in parallel
+
! style="width: 20%"|Parallel battery circuits
−
! style="text-align:left;"| = Total Ah required (step 4) ÷ Chosen battery Ah rating
+
! style="text-align:left;"| = Total Ah required (Step 4) ÷ Chosen battery Ah rating
 
|-
 
|-
 
|
 
|
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|-
 
|-
 
|
 
|
−
| style="text-align:left;"| = Round up to 1 × 55 Ah battery.
+
| style="text-align:left;"| = Round up to 1 parallel battery circuit (1 battery)
 
|}
 
|}
−
 
−
https://www.mkbattery.com/application/files/2715/6158/6466/8A22NF-DEKA_Spec_Sheet.pdf
 
  
 
'''Step 7: Calculate final Ah capacity'''<br />
 
'''Step 7: Calculate final Ah capacity'''<br />
 
{| class="wikitable" border=1 style="width: 80%;"
 
{| class="wikitable" border=1 style="width: 80%;"
 
! style="width: 20%"|Final Ah capacity
 
! style="width: 20%"|Final Ah capacity
−
! style="text-align:left;"| = Number of batteries in parallel (Step 7) × Chosen battery Ah rating
+
! style="text-align:left;"| = Parallel battery circuit (Step 6) × Chosen battery Ah rating
 
|-
 
|-
 
|
 
|
−
| style="text-align:left;"| = 1 battery in parallel × 55 Ah = 55Ah
+
| style="text-align:left;"| = 1 parallel battery circuit × 55 Ah = 55Ah
 
|}
 
|}
  
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*'''Module mismatch parameter =''' 1
 
*'''Module mismatch parameter =''' 1
 
*'''Mounting system temperature adder =''' 20°C for a pole mount
 
*'''Mounting system temperature adder =''' 20°C for a pole mount
−
*'''PV source temperature loss parameter ='''  -.48%/°C
+
*'''Temperature coefficient of max power %/°C ='''  -.48%/°C
  
−
::{| class="wikitable" border=1 style="width: 80%;"
+
{| class="wikitable" border=1 style="width: 80%;"
 
! style="width: 20%"|PV source temperature loss parameter
 
! style="width: 20%"|PV source temperature loss parameter
 
! style="text-align:left;"| = 1 + (Maximum ambient temperature + Mounting system temperature adder - 25°C) x Temperature coefficient of max power %/°C ÷ 100
 
! style="text-align:left;"| = 1 + (Maximum ambient temperature + Mounting system temperature adder - 25°C) x Temperature coefficient of max power %/°C ÷ 100
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|}
 
|}
  
−
::{| class="wikitable" border=1 style="width: 80%;"
+
{| class="wikitable" border=1 style="width: 80%;"
 
! style="width: 20%"|Total PV source loss parameter
 
! style="width: 20%"|Total PV source loss parameter
 
! style="text-align:left;"| = Module degradation parameter × Shading loss parameter × Soiling loss parameter × Wiring loss parameter × Module mismatch parameter × PV source temperature loss parameter
 
! style="text-align:left;"| = Module degradation parameter × Shading loss parameter × Soiling loss parameter × Wiring loss parameter × Module mismatch parameter × PV source temperature loss parameter
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==[[PWM charge controller sizing and selection]]==
 
==[[PWM charge controller sizing and selection]]==
 
====Step 1: Determine PV module power rating====
 
====Step 1: Determine PV module power rating====
−
The chosen [[System voltage parameter|System voltage]] limits the choices of modules and configurations that are possible with a PWM charge controller. A 12 volt system requires 1 ×36-cell module per string. The minimum size was determined to be 52 W. A 80 W polycrystalline PV module will be used for the design.
+
The chosen [[DC system voltage]] limits the choices of modules and configurations that are possible with a PWM charge controller. A 12 volt system requires 1 × 36-cell module per string. The minimum size was determined to be 52 W.<br />
 +
A Dasol 80 W, 36-cell polycrystalline PV module will be used for the design. [http://www.opensourcesolar.org/w/downloads/specsheets/DSA1880-11340767037.pdf Specifications sheet]
 +
 
 +
Module specifications:
 +
*Power = 80 W
 +
*Open circuit voltage (Voc) = 22.3 V
 +
*Short circuit current (Isc) = 4.85 A
 +
*Max power voltage (Vmp) = 18.0 V
 +
*Max power current (Imp) = 4.44 A
 +
*Temperature coefficient of open circuit voltage (TkVoc) = -.36 %/°C
 +
*Temperature coefficient of max power (TkPmp) = Not available.
  
 
{| class="wikitable" border=1 style="width: 80%;"
 
{| class="wikitable" border=1 style="width: 80%;"
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{| class="wikitable" border=1 style="width: 80%;"
 
{| class="wikitable" border=1 style="width: 80%;"
−
! style="width: 20%"|Minimum number of modules in parallel
+
! style="width: 20%"|Minimum number of PV source circuits
 
! style="text-align:left;"| = Minimum number of PV modules ÷ Number of modules in series (Step 1)
 
! style="text-align:left;"| = Minimum number of PV modules ÷ Number of modules in series (Step 1)
 
|-
 
|-
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{| class="wikitable" border=1 style="width: 80%;"
 
{| class="wikitable" border=1 style="width: 80%;"
 
! style="width: 20%"|Proposed PV source low insolation production
 
! style="width: 20%"|Proposed PV source low insolation production
−
! style="text-align:left;"| = PV module power rating (Step 1) × Minimum number of PV modules (Step 2) × [[Minimum PV source size#Step 1: Deteremine PV source loss parameters|Total PV source loss parameter]] × [[Load and solar resource comparison|Design insolation]] × [[Minimum PV source size#Step 2: Charge controller efficiency parameter|Charge controller efficiency parameter]] × [[Minimum PV source size#Step 4: Energy storage efficiency parameter|Energy storage efficiency parameter]]
+
! style="text-align:left;"| = PV module power rating (Step 1) × Minimum number of PV modules (Step 2) × [[Minimum PV source size#Step 1: Deteremine PV source loss parameters|Total PV source loss parameter]] × [[Load and solar resource comparison|Design daily insolation]] × [[Minimum PV source size#Step 2: Charge controller efficiency parameter|Charge controller efficiency parameter]] × [[Minimum PV source size#Step 4: Energy storage efficiency parameter|Energy storage efficiency parameter]]
 
|-
 
|-
 
|
 
|
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{| class="wikitable" border=1 style="width: 80%;"
 
{| class="wikitable" border=1 style="width: 80%;"
 
! style="width: 20%"|Daily excess production in Ah
 
! style="width: 20%"|Daily excess production in Ah
−
! style="text-align:left;"| = (Proposed PV source low insolation production - [[Load and solar resource comparison|Average daily watt-hours required]]) ÷ [[System voltage parameter]]
+
! style="text-align:left;"| = (Proposed PV source low insolation production - [[Load and solar resource comparison|Design daily watt-hours required]]) ÷ [[DC system voltage]]
 
|-
 
|-
 
|
 
|
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{| class="wikitable" border=1 style="width: 80%;"
 
{| class="wikitable" border=1 style="width: 80%;"
 
! style="width: 20%"|Ah used at full depth of discharge
 
! style="width: 20%"|Ah used at full depth of discharge
−
! style="text-align:left;"| = [[Energy storage sizing and selection#Step 7: Calculate final Ah capacity|Final Ah capacity]] × [[Energy storage sizing and selection#Step 1: Determine depth of discharge parameter|Depth of discharge parameter]]
+
! style="text-align:left;"| = [[Energy storage sizing and selection|Final Ah capacity]] × [[Energy storage sizing and selection#Step 1: Determine depth of discharge parameter|Depth of discharge parameter]]
 
|-
 
|-
 
|
 
|
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|}
 
|}
  
−
The battery will be able to reach full state of charge while using loads in 4.4 days, which is less than the maximum of 7 days. The design is okay.
+
<span style="color:#FFFFFF; background:#008000">'''The battery will be able to reach full state of charge while using loads in 4.4 days, which is less than the maximum of 7 days. The design is okay.'''</span>
  
 
====Step 4: Verify charging current====
 
====Step 4: Verify charging current====
−
This system will use an AGM battery, so its charge current should be between .05 (5%) and .2 (20%) of its C/20 rating.
+
This system will use an AGM battery, so that charge current from the PV source should be between .05 (5%) and .2 (20%) of its C/20 rating.
−
 
 
−
{| class="wikitable" border=1 style="width: 80%;"
 
−
! style="width: 20%"|Minimum required charge current
 
−
! style="text-align:left;"| = [[Energy storage sizing and selection#Step 7: Calculate final Ah capacity|Final Ah capacity]] × .05
 
−
|-
 
−
|
 
−
| = 55 Ah × .05 = 2.75 A
 
−
|}
 
  
 
It is necessary to check the minimum required charge current against the available charge current from the proposed PV source power rating.
 
It is necessary to check the minimum required charge current against the available charge current from the proposed PV source power rating.
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{| class="wikitable" border=1 style="width: 80%;"
 
{| class="wikitable" border=1 style="width: 80%;"
 
! style="width: 20%"|Available charging current
 
! style="width: 20%"|Available charging current
−
! style="text-align:left;"| = [[PV module#Standard test conditions|Maximum power current (Imp)]] × Minimum number of PV modules in parallel
+
! style="text-align:left;"| = [[PV module#Standard test conditions|Maximum power current (Imp)]] × Minimum number of PV source circuits
 
|-
 
|-
 
|
 
|
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{| class="wikitable" border=1 style="width: 80%;"
 
{| class="wikitable" border=1 style="width: 80%;"
 
! style="width: 20%"|Percentage of C/20 rate
 
! style="width: 20%"|Percentage of C/20 rate
−
! style="text-align:left;"| = Available charging current ÷ [[Energy storage sizing and selection#Step 7: Calculate final Ah capacity|Final Ah capacity]]
+
! style="text-align:left;"| = Available charging current ÷ [[Energy storage sizing and selection|Final Ah capacity]]
 
|-
 
|-
 
|
 
|
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|}
 
|}
  
−
The PV source can supply .08 (8%) of the C/20 current rating of the energy storage system, which is more than .05 (5%) and less than .2 (20%). The PV source configuration is okay.
+
<span style="color:#FFFFFF; background:#008000">'''The PV source can supply .08 (8%) of the C/20 current rating of the energy storage system, which is more than .05 (5%) and less than .2 (20%). The PV source configuration is okay.'''</span>
  
 
====Step 5: Determine final number of PV modules====
 
====Step 5: Determine final number of PV modules====
−
Determine a final number of modules and a series/parallel configuration that can meet the requirements of Step 1, Step 2, Step 3, and Step 4.
+
Determine a final number of modules and a PV source circuit configuration that can meet the requirements of Step 1, Step 2, Step 3, and Step 4.
  
 
{| class="wikitable" border=1 style="width: 80%;"
 
{| class="wikitable" border=1 style="width: 80%;"
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{| class="wikitable" border=1 style="width: 80%;"
 
{| class="wikitable" border=1 style="width: 80%;"
−
! style="width: 20%"|Final number of PV modules in parallel
+
! style="width: 20%"|Final number of PV source circuits
 
! style="text-align:left;"| = 1
 
! style="text-align:left;"| = 1
 
|}
 
|}
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{| class="wikitable" border=1 style="width: 80%;"
 
{| class="wikitable" border=1 style="width: 80%;"
 
! style="width: 20%"|Total PV source current
 
! style="width: 20%"|Total PV source current
−
! style="text-align:left;"| = Final number of PV modules (Step 5) × [[PV module|Isc rating]] of chosen module (Step 1) × [[Irradiance safety parameter|Irradiance safety parameter]]
+
! style="text-align:left;"| = Final number of PV source circuits (Step 5) × [[PV module|Isc rating]] of chosen module (Step 1) × [[Irradiance safety parameter|Irradiance safety parameter]]
 
|-
 
|-
 
|
 
|
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====Step 7: Select a charge controller====
 
====Step 7: Select a charge controller====
 
The final chosen charge controller should:
 
The final chosen charge controller should:
−
#Function at the [[System voltage parameter|system voltage]].
+
#Function at the [[DC system voltage]].
 
#The charge controller(s) should have a total current rating that is larger than the minimum current rating (Step 6).
 
#The charge controller(s) should have a total current rating that is larger than the minimum current rating (Step 6).
 +
 +
A Morningstar SHS-10 PWM charge controller will be used. [http://www.opensourcesolar.org/w/downloads/specsheets/SHS_ENG_R2_1_12lowres.pdf Specifications sheet] [http://www.opensourcesolar.org/w/downloads/dataheets/SHSmanualTranslated.pdf Multi-lingual user manual]
 +
 +
:Specifications:
 +
:*Charge controller type: PWM
 +
:*Nominal output voltage: 12 V
 +
:*Maximum current rating: 10 A
  
 
The result of the following equation should always be rounded up.
 
The result of the following equation should always be rounded up.
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|-
 
|-
 
|
 
|
−
| = 6.1 A ÷ 10 A = .61 = 1 (rounded up to 1 charge controller)
+
| = 6.1 A ÷ 10 A = .61 = 1 (round up to 1 charge controller)
 
|}
 
|}
  
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{| class="wikitable" border=1 style="width: 80%;"
 
{| class="wikitable" border=1 style="width: 80%;"
 
! style="width: 20%"|PV source power rating
 
! style="width: 20%"|PV source power rating
−
! style="text-align:left;"| = PV module power rating (Step 1) × Final number of PV modules in parallel (Step 5)
+
! style="text-align:left;"| = PV module power rating (Step 1) × Final number of PV modules (Step 5)
 
|-
 
|-
 
|
 
|
 
| = 80 W × 1 = 80 W
 
| = 80 W × 1 = 80 W
 
|}
 
|}
 +
 +
====Step 9: Verify PV source and charge controller compatability====
 +
PWM charge controllers often have a maximum PV source power rating in watts that limits the size of the PV source. Verify that the maximum PV source power rating is greater than the final PV source power rating. If it is not, the charge controller size needs to be increased.
 +
 +
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 20%"|PV source and charge controller compatability
 +
! style="text-align:left;"| = Final PV source power rating must be ''less than'' the maximum PV source power rating of the charge controller
 +
|-
 +
|
 +
| = 80 W PV source is less than 170 W maximum input power rating of charge controller
 +
|}
 +
 +
<span style="color:#FFFFFF; background:#008000">'''The PV source and charge controller are compatible.'''</span>
  
 
==[[Wire, overcurrent protection, and disconnect sizing and selection]]==
 
==[[Wire, overcurrent protection, and disconnect sizing and selection]]==
 +
The chosen wire for a circuit must meet the requirements set out in each phase of this process. The wire size must be increased if it fails to meet any of these phases and then the process must be performed again with the new wire size.
 +
 
===PV source circuit===
 
===PV source circuit===
−
 
−
If a wire size meets the current requirements determined in Phase 2 but fails to meet either the overcurrent protection requirements in Phase 3 or the voltage drop requirements in Phase 4, then the wire size will have to be increased.
 
  
 
====Phase 1: Maximum circuit current====
 
====Phase 1: Maximum circuit current====
−
 
 
{| class="wikitable" border=1 style="width: 80%;"
 
{| class="wikitable" border=1 style="width: 80%;"
 
! style="width: 33%"|Maximum circuit current
 
! style="width: 33%"|Maximum circuit current
−
! style="text-align:left;"| = [[PV module#Module ratings|PV module Isc]] × [[Irradiance safety parameter]]
+
! style="text-align:left;"| = [[PV module|PV module Isc]] × [[Irradiance safety parameter]]
 
|-
 
|-
 
|
 
|
Line 567: Line 590:
  
 
====Phase 2: Wire ampacity====
 
====Phase 2: Wire ampacity====
−
There will only be two current-carrying conductors in the conduit. The maximum ambient temperature is
+
There will only be two current-carrying conductors in the conduit. The maximum ambient temperature 23°C. 90°C wet/dry rated PV wire will be used for this circuit.
  
−
The minimum wire size for a circuit can be determined by:
+
The minimum wire size for a circuit can be using the following steps:
 
<ol>
 
<ol>
−
<li>Determine the ambient temperature correction factor based upon the [[Weather and solar resource evaluation#Maximum ambient temperature|maximum ambient temperature]] for outdoor circuits and [[Weather and solar resource evaluation#Maximum indoor temperature|maximum indoor temperature]] for indoor circuits using the [[#Ambient temperature correction factor table|ambient temperature correction factor table]]. High temperatures increase the resistance of the wire and reduce its current carrying capacity.<br />'''Note:''' Wires, nor conduit, should be located less than 2.25 cm from a roof surface in direct sunlight. This will increase temperatures as much as 33°C and can lead to the ampacity and temperature rating of wires to be exceeded.</li>
+
<li>Determine the ambient temperature correction factor based upon the [[Weather and solar resource evaluation|maximum ambient temperature]] using the [[Wire, overcurrent protection, and disconnect sizing and selection#Ambient temperature correction factor table|ambient temperature correction factor table]]. The ambient temperature correction factor for this circuit is 1.05 because it is a 90°C wet/dry rated wire with a maximum ambient temperature of 23°C.
−
<li>Determine the conduit correction factor based upon the number of wires in the conduit using the [[#Conduit correction factor table|conduit correction factor table]]. More than three wires - not including any wires related to the grounding system - in a conduit will reduce the current carrying capacity of each wires due to reduced cooling.</li>
+
<li>Determine the conduit fill correction factor based upon the number of number of conductors in the conduit using the [[Wire, overcurrent protection, and disconnect sizing and selection#Conduit fill correction factor table|conduit fill correction factor table]] There will only be two current-carrying conductors in the conduit, so the conduit correction fill factor is 1.</li>
−
<li>Determine the total wire correction parameter based upon the smaller of: the Ambient temperature correction multiplied by the conduit adjustment factor '''or''' .8 (a safety factor from the US National Electrical code).</li>
+
<li>Determine the total wire correction parameter based upon the smaller of: the Ambient temperature correction multiplied by the Conduit fill  correction factor '''or''' .8 (a safety factor from the US National Electrical code).</li>
 
{| class="wikitable" border=1 style="width: 80%;"
 
{| class="wikitable" border=1 style="width: 80%;"
 
! style="width: 20%"|Total wire correction parameter
 
! style="width: 20%"|Total wire correction parameter
−
! style="text-align:left;"| = Smaller of (Ambient temperature correction factor (Step 1) × Conduit correction factor (Step 2)) '''or''' .8
+
! style="text-align:left;"| = Smaller of (Ambient temperature correction factor × Conduit fill correction factor) '''or''' .8
 +
|-
 +
|
 +
| = Smaller of (1.05 × 1) or .8 = .8
 
|}
 
|}
−
<li>Determine minimum wire ampacity. Divide the maximum circuit current by the total wire correction factor (Step 3)</li>
+
 
 +
<li>Determine minimum wire ampacity. Divide the maximum circuit current (Phase 1) by the total wire correction factor (Step 3)</li>
 
{| class="wikitable" border=1 style="width: 80%;"
 
{| class="wikitable" border=1 style="width: 80%;"
 
! style="width: 20%"|Minimum wire ampacity
 
! style="width: 20%"|Minimum wire ampacity
−
! style="text-align:left;"| = Maximum circuit current ÷ Total wire correction parameter (Step 3)
+
! style="text-align:left;"| = Maximum circuit current (Phase 1) ÷ Total wire correction parameter (Step 3)
 +
|-
 +
|
 +
| = 6.1 A ÷ .8 = 7.6 A
 
|}
 
|}
−
<li>Select a wire size with a maximum rated ampacity equal to or above the minimum wire ampacity calculated in the previous step using the [[#Allowable wire ampacities|allowable wire ampacities table]]. This table has three different temperature columns - 60°C, 75°C / 90°C – that correspond to different [[Types of conductors|wire types]]. This temperature corresponds to the maximum temperature rating of the wire type, which should be labeled on the exterior of the wire and readily available from the product provider. Most wires have a dual rating of 60°C (wet)/75°C (dry), 75°C, or 90°C rating. If 60°C wire is used in the circuit, the 60°C column will have to be used.
+
 
 +
<li>Select a wire size with a maximum rated ampacity equal to or above the minimum wire ampacity calculated in the previous step using the [[Wire, overcurrent protection, and disconnect sizing and selection#Conductor ampacity table|allowable wire ampacity table]]. A 4 mm² / 12 AWG, 90°C wet/dry rated PV wire with an ampacity rating of 25 A will be used for this circuit as this is a commonly used wire type for a circuit of this type. 25 A is larger than the required 7.6 A ampacity.
 
</li>
 
</li>
 
</ol>
 
</ol>
  
 
====Phase 3: Overcurrent protection and disconnects====
 
====Phase 3: Overcurrent protection and disconnects====
−
[[File:Breakerslabeled201201.png|thumb|Wiring diagram of a stand-alone PV system with a charge controller with DC lighting control and an inverter for AC loads. All potential overcurrent protection devices are labeled, but all may not be necessary.]]
 
−
[[File:Disconncetslabeled-design.png|thumb|Wiring diagram of a stand-alone PV system with a charge controller with DC lighting control and an inverter for AC loads. Equipment disconnects for PV modules provided by [[Module connectors|module connectors]]. All other required disconnects are labeled.]]
 
−
No wire should be exposed to current in excess of its rated capacity under the conditions of use. If a power source that a circuit is connected to can supply more current than the rated ampacity of a wire, then an [[:Category:Overcurrent protection and disconnects|overcurrent protection device]] must be used to prevent it from overheating and starting a fire. In off-grid systems overcurrent protection devices are also typically used as [[Disconnects|power source disconnects]] and [[Disconnects|equipment disconnects]]. [[Residual current device|Residual current devices]] should be sized using this same method if they are intended to function as an OCPD, if not they only need to be larger than the maximum current of the circuit to ensure that they do not accidentally trip.
 
  
−
[[Ground fault protection device|Ground fault protection devices]] incorporate a breaker, but these GFPDs only come in a few sizes and it is common to use a GFPD with a breaker that is substantially larger than the ampacity of the wire for this reason. An additional breaker is therefore commonly used as the power source disconnect, because using the GFPD would mean that the DC system bond would be removed each time the breaker was used as a disconnect, which is not a safe practice.
+
This circuit, since it only has 1 PV module, does not require an OCPD, but one will be located near the PV equipment to provide a PV power source disconnect.
  
−
There are some cases in which an overcurrent protection device is not required because another overcurrent protection device protects that circuit against excessive current or the power source cannot supply current that would exceed the rated capacity of the wire. Not all systems are wired the same - some designs will require additional OCPDs and others will require fewer.
+
The appropriate overcurrent protection device size can be determined by:
  
−
{| class="wikitable" border=1
+
<ol>
−
!Circuit
+
<li>Determine the minimum size
−
!
+
</li>
 +
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 20%"|Minimum OCPD size
 +
! style="text-align:left;"| = Maximum circuit current (Phase 1) × 1.25
 
|-
 
|-
−
|(1) PV source circuit OCPD
+
|
−
|Required if the system has more than two parallel strings of PV modules. Can also serve as the required [[Disconnects|power source disconnect]] - see (10) in the image.
+
| = 6.1 A × 1.25 = 7.6 A
 +
|}
 +
<li>A standard 10 A DC breaker will be used. This breaker is larger than the required minimum OCPD size and smaller than the rated 25 A ampacity of the wire that it will protect. The PV source is current limited and the wire is sized to handle the maximum current, therefore it is not necessary to verify the OCPD size.</li>
 +
 
 +
</ol>
 +
 
 +
<span style="color:#FFFFFF; background:#008000">'''The OCPD size is okay.'''</span>
 +
 
 +
====Phase 4: Voltage drop====
 +
If the voltage drop for the wire chosen in Phase 2 for a particular circuit is not within the [[Wire, overcurrent protection, and disconnect sizing and selection#Recommended circuit voltage drop values|recommended values]], then using a larger sized wire should be considered. Increasing the wire size will not affect any other part of this process; the calculated OCPD size can remain the same.
 +
 
 +
This circuit will be 6 meters long one-way. It is 4 mm² / 12 AWG, wire with a resistance value in (Ω/Km) of 6.73 Ω. It is recommended that the voltage drop between the PV source and the charge controller be kept below 3%.
 +
 
 +
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 20%"|PV source circuit current
 +
! style="text-align:left;"| = Max power current of the PV module
 
|-
 
|-
−
|(2) PV output circuit OCPD
+
|
−
|A power source disconnect - typically a breaker - is required for the PV source. If the PV source circuits have breakers they can meet this need if they are located near the charge controller. Can also serve as the required [[Disconnects|power source disconnect]] - see (10) in the image.
+
| = 4.44 A
 +
|}
 +
 
 +
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 20%"|PV source circuit nominal voltage
 +
! style="text-align:left;"| = Number of PV modules in series × Max power voltage of the PV module
 
|-
 
|-
−
|(3) Charge controller output circuit OCPD
+
|
−
|The wires between the charge controller and the energy storage system must be protected by an OCPD. There should also be a power source disconnect for the energy storage system and an equipment disconnect for the charge controller. Both of these requirements can be fulfilled by installing a breaker - see (11) in the image.
+
| = 18 V × 1 = 18 V
 +
|}
 +
 
 +
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 20%"|Voltage drop
 +
! style="text-align:left;"| = 2 x Circuit current x One-way circuit length (m) x  [[Wire, overcurrent protection, and disconnect sizing and selection#Wire resistance values|Resistance (Ω/Km)]] ÷ 1000
 
|-
 
|-
−
|(4) Charge controller load circuit OCPD
+
|
−
|The wires between the charge controller and any lighting/load only need to be protected by an OCPD if the charge controller can supply current that exceeds the rating of the wires. This is typically not the case.
+
| = 2 × 4.44 A × 6m × 6.73 Ω ÷ 1000 = .36 V
 +
|}
 +
 
 +
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 20%"|Percentage voltage drop
 +
! style="text-align:left;"| = Voltage drop ÷ nominal circuit voltage x 100
 
|-
 
|-
−
|(5) DC branch circuit OCPD
+
|
−
|The wires between the charge controller and any lighting/loads only need to be protected by an OCPD if the charge controller can supply current that exceeds the rating of the wires. This is typically not the case.
+
| = .36 V ÷ 18 V × 100 = 2%
 +
|}
 +
 
 +
<span style="color:#FFFFFF; background:#008000">'''2% voltage drop for this circuit is acceptable. The wire size is okay.'''</span>
 +
 
 +
===Charge controller output circuit/battery circuit===
 +
This same size wire will be used from the charge controller to the battery with one overcurrent protection device which will also serve as a power source disconnect.
 +
====Phase 1: Maximum circuit current====
 +
 
 +
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 33%"|Maximum circuit current
 +
! style="text-align:left;"| = Current rating of the charge controller
 
|-
 
|-
−
|(6) Inverter input circuit OCPD
+
|
−
|The wires between the inverter and the energy storage system must be protected by an OCPD. There should also be a power source disconnect for the energy storage system and an equipment disconnect for the inverter. Both of these requirements can be fulfilled by installing a breaker - see (13) in the image.
+
| = 10 A
 +
|}
 +
 
 +
====Phase 2: Wire ampacity====
 +
There will only be two current-carrying conductors in the conduit. The maximum indoor temperature 20°C. 75° wet / 90°C dry rated wire will be used for this circuit.
 +
 
 +
The minimum wire size for a circuit can be using the following steps:
 +
<ol>
 +
<li>Determine the ambient temperature correction factor based upon the [[Weather and solar resource evaluation#Maximum ambient temperature|maximum ambient temperature]] using the [[Wire, overcurrent protection, and disconnect sizing and selection#Ambient temperature correction factor table|ambient temperature correction factor table]]. The ambient temperature correction factor for this circuit is 1.11 because it is a 75° wet / 90°C dry rated wire with a maximum indoor temperature of 20°C.
 +
<li>Determine the conduit fill correction factor based upon the number of number of conductors in the conduit using the [[Wire, overcurrent protection, and disconnect sizing and selection#Conduit fill correction factor table|conduit fill correction factor table]] There will only be two current-carrying conductors in the conduit, so the conduit correction fill factor is 1.</li>
 +
<li>Determine the total wire correction parameter based upon the Ambient temperature correction multiplied by the Conduit fill correction factor</li>
 +
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 20%"|Total wire correction parameter
 +
! style="text-align:left;"| = Ambient temperature correction factor × Conduit fill correction factor
 
|-
 
|-
−
|(7) Inverter output circuit OCPD
+
|
−
|The wires between the inverter and any loads only need to be protected by an OCPD if the inverter can supply current that exceeds the rating of the wires. This is often not the case with smaller inverters, especially those operating at 220V. It is recommended that a [[Residual current device|residual current device (RCD)]] with an integrated breaker is used on the output of the inverter to increase system safety or on each individual circuit. It should be located before the [[Grounding system|AC system bonding jumper]] to avoid accidental tripping (activation).
+
| = 1.11 × 1 = 1.11
 +
|}
 +
 
 +
<li>Determine minimum wire ampacity. Divide the maximum circuit current (Phase 1) by the total wire correction factor (Step 3)</li>
 +
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 20%"|Minimum wire ampacity
 +
! style="text-align:left;"| = Maximum circuit current (Phase 1) ÷ Total wire correction parameter (Step 3)
 
|-
 
|-
−
|(8) AC branch circuit OCPD
+
|
−
|The wires between the inverter and any loads only need to be protected by an OCPD if the inverter can supply current that exceeds the rating of the wires. This is often not the case with smaller inverters, especially those operating at 220V. If there is no [[Residual current device|residual current device (RCD)]] on the output circuit of the inverter, it is recommended that one be added to AC circuit or outlet.
+
| = 10 A ÷ 1.11 = 9.0 A
−
|-
 
−
|(9) Energy storage circuit OCPD
 
−
|The wires between the energy storage system and any other component must be protected by an OCPD - charge controllers, inverters, DC-DC converters, low voltage disconnects, DC appliances. There also must be a power source disconnect for the energy storage system. Both of these requirements can be fulfilled by installing a breaker or a fused disconnect - see (12) in the image. Larger systems are typically designed like in the wiring diagram with one single circuit running from the energy storage system to common DC busbars to reduce wire and OCPD costs - in this case there is an energy storage circuit. Smaller systems often connect the charge controller and inverter directly to the energy storage system independently - in this case there is no energy storage circuit.
 
 
|}
 
|}
 +
 +
<li>Select a wire size with a maximum rated ampacity equal to or above the minimum wire ampacity calculated in the previous step using the [[Wire, overcurrent protection, and disconnect sizing and selection#Conductor ampacity table|allowable wire ampacity table]]. A 4 mm² / 12 AWG, 75° wet / 90°C dry rated wire with an ampacity rating of 25 A will be used for this circuit as this is a commonly used wire type for a circuit of this type. 25 A is larger than the required 9.0 A ampacity.
 +
</li>
 +
</ol>
 +
 +
====Phase 3: Overcurrent protection and disconnects====
 +
This circuit requires an OCPD/disconnect as it is connected directly to the battery which is a power source. An OCPD size should be chosen from the [[Wire, overcurrent protection, and disconnect sizing and selection#Phase 3: Overcurrent protection and disconnects|list of standard OCPD sizes]]. If the current rating of the chosen OCPD size is larger than the maximum OCPD size under conditions of use, then the wire size must be increased the next size.
  
 
The appropriate overcurrent protection device size can be determined by:
 
The appropriate overcurrent protection device size can be determined by:
  
 
<ol>
 
<ol>
−
<li>Overcurrent protection devices (OCPDs) are thermally (heat) activated. If an OCPD operates for an extended period of time, it will begin to generate heat that could potentially cause it to accidentally activate. Thus, if a circuit will operate for more than three hours continuously, which all circuits in an off-grid system likely will at some point, then the overcurrent protection device size will be increased to avoid any issues. The maximum circuit current calculated in Phase 1 is multiplied by the therefore multiplied by the [[Continuous duty safety parameter|continuous duty safety parameter]] of 1.25.
+
<li>Determine the minimum size
 
</li>
 
</li>
 
{| class="wikitable" border=1 style="width: 80%;"
 
{| class="wikitable" border=1 style="width: 80%;"
 
! style="width: 20%"|Minimum OCPD size
 
! style="width: 20%"|Minimum OCPD size
 
! style="text-align:left;"| = Maximum circuit current (Phase 1) × 1.25
 
! style="text-align:left;"| = Maximum circuit current (Phase 1) × 1.25
 +
|-
 +
|
 +
| = 10 A × 1.25 = 12.5 A
 
|}
 
|}
−
<li>There are standard OCPD sizes that both the NEC and IEC recognize. The OCPD size should be the next largest size after the minimum OCPD size calculated in Step 1.
+
<li>A standard 15 A DC breaker will be used. This breaker is larger than the required minimum OCPD size, but smaller than the 25 A rated ampacity of the wire that it will protect.</li>
  
−
*Standard international OCPD sizes:  1 A, 2 A, 4 A, 6 A, 10 A, 13 A, 16 A, 20 A, 25 A, 32 A, 40 A, 50 A, 63 A, 80 A, 100 A and 125 A.<br/>
+
<li>Verify that the chosen OCPD size from Step 2 will protect the wire size chosen in Phase 2 from excessive current under the conditions of use. The current rating of the chosen OCPD size (Step 2) must be less than the calculated maximum current under conditions of use ''unless'' the calculated maximum current under conditions of use is between standard OCPD values, in this case the next largest OCPD size is used from the [[Wire, overcurrent protection, and disconnect sizing and selection#Phase 3: Overcurrent protection and disconnects|list of standard OCPD sizes]]. If the current rating of the chosen OCPD size is larger than the maximum OCPD size under conditions of use, then the wire size must be increased until it passes this test.
−
*Standard US OCPD sizes per US NEC: 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200, 1600, 2000, 2500, 3000, 4000 5000, and 6000 A. Additional standard fuse sizes are 1, 3, 6, 10, and 601 A.</li>
+
 
 +
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 20%"|Maximum current under conditions of use
 +
! style="text-align:left;"| = [[Wire, overcurrent protection, and disconnect sizing and selection#Conductor ampacity table|Wire ampacity from allowable wire ampacity table]] × Total wire correction parameter (Phase 2).
 +
|-
 +
|
 +
| = 25 A × 1.11 = 27.75 A
 +
|}
  
−
<li>Verify that the chosen OCPD size from Step 2 will protect the wire size chosen in Phase 2 from excessive current under the conditions of use. The current rating of the chosen breaker size (Step 2) must be less than the calculated maximum current under conditions of use ''unless'' the calculated maximum current under conditions of use is between standard OCPD values, in this case the next largest breaker can be chosen.
+
Determine the maximum OCPD size under conditions of use.
 +
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 20%"|Maximum OCPD size under conditions of use
 +
! style="text-align:left;"| = Can be equal to the maximum current under conditions of use. If between standard OCPD sizes, the next largest OCPD is used. Except for the following wire sizes: 15 A maximum for 2.5 mm² / 14 AWG. 20 A maximum for 4 mm² / 12 AWG. 30 A maximum for 6 mm² / 10 AWG.
 +
|-
 +
|
 +
| = 20 A OCPD
 +
|}
  
 
{| class="wikitable" border=1 style="width: 80%;"
 
{| class="wikitable" border=1 style="width: 80%;"
−
! style="width: 20%"|Maximum current under conditions of use
+
! style="width: 20%"|Verify OCPD under conditions of use
−
! style="text-align:left;"| = [[#Allowable wire ampacities|Wire ampacity from allowable wire ampacities table]] × Total wire correction parameter (Phase 2).
+
! style="text-align:left;"| = The current rating of the chosen OCPD (Step 2) must be ''less than or equal to'' the maximum OCPD size under conditions of use
 +
|-
 +
|
 +
| = 15 A OCPD is less than 20 A OCPD maximum size
 +
|}
 +
</ol>
 +
 
 +
<span style="color:#FFFFFF; background:#008000">'''The OCPD and wire size are okay.'''</span>
 +
 
 +
====Phase 4: Voltage drop====
 +
If the voltage drop for the wire chosen in Phase 2 for a particular circuit is not within the [[Wire, overcurrent protection, and disconnect sizing and selection#Recommended circuit voltage drop values|recommended values]], then using a larger sized wire should be considered. Increasing the wire size will not affect any other part of this process; the calculated OCPD size can remain the same.
 +
 
 +
This circuit will be 1.5 meters long one-way. It is 4 mm² / 12 AWG, wire with a resistance value in (Ω/Km) of 6.73 Ω. It is recommended that the voltage drop between the charge controller and the energy storage system be kept below 1.5%. The circuit current is the Imp of the PV module: 4.44 A. The nominal circuit voltage is the [[DC system voltage]]: 12 V.
 +
 
 +
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 20%"|Voltage drop
 +
! style="text-align:left;"| = 2 x Circuit current x One-way circuit length (m) x  [[Wire, overcurrent protection, and disconnect sizing and selection#Wire resistance values|Resistance (Ω/Km)]] ÷ 1000
 +
|-
 +
|
 +
| = 2 × 4.44 A × 1.5m × 6.73 Ω ÷ 1000 = .09 V
 +
|}
 +
 
 +
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 20%"|Percentage voltage drop
 +
! style="text-align:left;"| = Voltage drop ÷ Nominal circuit voltage voltage x 100
 +
|-
 +
|
 +
| = .09 V ÷ 12 V × 100 = .75%
 +
|}
 +
 
 +
<span style="color:#FFFFFF; background:#008000">'''.75% voltage drop for this circuit is acceptable. The wire size is okay.'''</span>
 +
 
 +
===Charge controller load circuit===
 +
 
 +
====Phase 1: Maximum circuit current====
 +
 
 +
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 33%"|Maximum circuit current
 +
! style="text-align:left;"| = Current rating of the charge controller lighting/load circuit
 +
|-
 +
|
 +
| = 10 A
 +
|}
 +
 
 +
====Phase 2: Wire ampacity====
 +
There will only be two current-carrying conductors in the conduit. The maximum indoor temperature 20°C. 75° wet / 90°C dry rated wire will be used for this circuit.
 +
 
 +
The minimum wire size for a circuit can be using the following steps:
 +
<ol>
 +
<li>Determine the ambient temperature correction factor based upon the [[Weather and solar resource evaluation#Maximum ambient temperature|maximum ambient temperature]] using the [[Wire, overcurrent protection, and disconnect sizing and selection#Ambient temperature correction factor table|ambient temperature correction factor table]]. The ambient temperature correction factor for this circuit is 1.11 because it is a 75° wet / 90°C dry rated wire with a maximum indoor temperature of 20°C.
 +
<li>Determine the conduit fill correction factor based upon the number of number of conductors in the conduit using the [[Wire, overcurrent protection, and disconnect sizing and selection#Conduit fill correction factor table|conduit fill correction factor table]] There will only be two current-carrying conductors in the conduit, so the conduit correction fill factor is 1.</li>
 +
<li>Determine the total wire correction parameter based upon the Ambient temperature correction multiplied by the Conduit fill  correction factor</li>
 +
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 20%"|Total wire correction parameter
 +
! style="text-align:left;"| = Ambient temperature correction factor × Conduit fill correction factor
 +
|-
 +
|
 +
| = 1.11 × 1 = 1.11
 +
|}
 +
 
 +
<li>Determine minimum wire ampacity. Divide the maximum circuit current (Phase 1) by the total wire correction factor (Step 3)</li>
 +
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 20%"|Minimum wire ampacity
 +
! style="text-align:left;"| = Maximum circuit current (Phase 1) ÷ Total wire correction parameter (Step 3)
 +
|-
 +
|
 +
| = 10 A ÷ 1.11 = 9.0 A
 
|}
 
|}
  
−
'''Example 1:''' Step 1,2 suggest a 30 A breaker. Phase 2 calculated a 10 AWG / 6 mm² for the circuit. The ampacity rating for this wire is 35 A at 75°C. The total wire correction parameter (Phase 2) is .65 Can the 10 AWG / 6mm² wire be used?
+
<li>Select a wire size with a maximum rated ampacity equal to or above the minimum wire ampacity calculated in the previous step using the [[Wire, overcurrent protection, and disconnect sizing and selection#Conductor ampacity table|allowable wire ampacity table]]. A 4 mm² / 12 AWG, 75° wet / 90°C dry rated wire with an ampacity rating of 25 A  will be used for this circuit as this is a commonly used wire type for a circuit of this type. 25 A is larger than the required 9.0 A ampacity.
 +
</li>
 +
</ol>
  
−
:Maximum current under conditions of use = 35 A × .65
+
====Phase 3: Overcurrent protection and disconnects====
−
:Maximum current under conditions of use = 22.75 A
+
This circuit does not require an OCPD if the available current is limited by another OCPD or the charge controller - in this case there is both a 15 A OCPD on the connection to the battery and the charge controller itself is current limited to 10 A - to a maximum current that is below the ampacity rating of the wire. It is necessary to check to make sure that the wire will be protected by the other OCPD under the conditions of use.
−
:The next largest breaker is a 25 A breaker, but this breaker would be too small for the circuit. The wire size needs to be increased to the next largest size of wire 8 AWG / 10mm²
 
  
 +
Verify that the nearest OCPD will protect the wire size chosen in Phase 2 from excessive current under the conditions of use. The current rating of the OCPD must be less than the calculated maximum current under conditions of use ''unless'' the calculated maximum current under conditions of use is between standard OCPD values, in this case the next largest OCPD size is used from the [[Wire, overcurrent protection, and disconnect sizing and selection#Phase 3: Overcurrent protection and disconnects|list of standard OCPD sizes]]. If the current rating of the chosen OCPD size is larger than the maximum OCPD size under conditions of use, then the wire size must be increased until it passes this test or an additional OCPD must be added to protect this circuit.
  
−
'''Example 2:''' Step 1,2 suggest a 30 A breaker. Phase 2 calculated a 10 AWG / 6 mm² for the circuit. The ampacity rating for this wire is 35 A at 75°C. The total wire correction parameter (Phase 2) is .8 Can the 10 AWG / 6mm² wire be used?
+
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 20%"|Maximum current under conditions of use
 +
! style="text-align:left;"| = [[Wire, overcurrent protection, and disconnect sizing and selection#Conductor ampacity table|Wire ampacity from allowable wire ampacity table]] × Total wire correction parameter (Phase 2).
 +
|-
 +
|
 +
| = 25 A × 1.11 = 27.8 A
 +
|}
  
−
:Maximum current under conditions of use = 35 A × .8
+
Determine the maximum OCPD size under conditions of use.
−
:Maximum current under conditions of use = 28 A
+
{| class="wikitable" border=1 style="width: 80%;"
−
:The next largest breaker is a 30 A breaker, which was the suggested breaker size (Step 1,2). 10 AWG / 6mm² and a 30 A breaker is acceptable.
+
! style="width: 20%"|Maximum OCPD size under conditions of use
 +
! style="text-align:left;"| = Can be equal to the maximum current under conditions of use. If between standard OCPD sizes, the next largest OCPD is used. Except for the following wire sizes: 15 A maximum for 2.5 mm² / 14 AWG. 20 A maximum for 4 mm² / 12 AWG. 30 A maximum for 6 mm² / 10 AWG.
 +
|-
 +
|
 +
| = 20 A OCPD
 +
|}
  
 +
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 20%"|Verify OCPD under conditions of use
 +
! style="text-align:left;"| = The current rating of the chosen OCPD (Step 2) must be ''less than or equal to'' the maximum OCPD size under conditions of use
 +
|-
 +
|
 +
| = 15 A OCPD is less than the maximum 20 A OCPD size
 +
|}
 
</ol>
 
</ol>
 +
 +
<span style="color:#FFFFFF; background:#008000">'''No additional OCPD is necessary'''</span>
  
 
====Phase 4: Voltage drop====
 
====Phase 4: Voltage drop====
−
All wires should be sized to make sure that the resistance of the wire will not create an excessive [[Voltage drop|voltage drop]] that can lead to lost PV production, improper battery charging, and loads that do not function properly. If the voltage drop for the wire chosen in Phase 2 for a particular circuit is not within the [[#Recommended circuit voltage drop values|recommended values]], then using a larger sized wire should be considered. Increasing the wire size will not affect any other part of this process; the calculated OCPD size can remain the same.
+
If the voltage drop for the wire chosen in Phase 2 for a particular circuit is not within the [[Wire, overcurrent protection, and disconnect sizing and selection#Recommended circuit voltage drop values|recommended values]], then using a larger sized wire should be considered. Increasing the wire size will not affect any other part of this process; the calculated OCPD size can remain the same.
  
−
The formula for calculating voltage drop is:
+
This circuit will be .25 meters long one-way. It is 4 mm² / 12 AWG, wire with a resistance value in (Ω/Km) of 6.73 Ω. It is recommended that the voltage drop between the charge controller be kept below 5% for any lights and below 3% for any loads. The circuit current is the current required by The circuit nominal voltage is the  Nominal circuit voltage is the [[DC system voltage]]: 12 V.
 +
 
 +
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 20%"|Charge controller load circuit current
 +
! style="text-align:left;"| = Power rating of all DC loads ÷ Nominal circuit voltage
 +
|-
 +
|
 +
| = 56 W ÷ 12 V = 4.67 A
 +
|}
  
 
{| class="wikitable" border=1 style="width: 80%;"
 
{| class="wikitable" border=1 style="width: 80%;"
 
! style="width: 20%"|Voltage drop
 
! style="width: 20%"|Voltage drop
−
! style="text-align:left;"| = 2 x Circuit current x One-way circuit length (m) x  [[#Conductor resistance values|Resistance (Ω/Km)]] ÷ 1000
+
! style="text-align:left;"| = 2 x Circuit current x One-way circuit length (m) x  [[Wire, overcurrent protection, and disconnect sizing and selection#Wire resistance values|Resistance (Ω/Km)]] ÷ 1000
 +
|-
 +
|
 +
| = 2 × 4.67 A × .25m × 6.73 Ω ÷ 1000 = .016 V
 
|}
 
|}
−
 
−
The most important value is the percentage voltage drop for the circuit. This is calculated using the formula:
 
  
 
{| class="wikitable" border=1 style="width: 80%;"
 
{| class="wikitable" border=1 style="width: 80%;"
 
! style="width: 20%"|Percentage voltage drop
 
! style="width: 20%"|Percentage voltage drop
−
! style="text-align:left;"| = Voltage drop ÷ Circuit operating voltage x 100
+
! style="text-align:left;"| = Voltage drop ÷ Nominal circuit voltage x 100
 +
|-
 +
|
 +
| = .016 V ÷ 12 V × 100 = .13%
 
|}
 
|}
  
−
====Recommended circuit voltage drop values====
+
<span style="color:#FFFFFF; background:#008000">'''.13% voltage drop for this circuit is acceptable. The wire size is okay.'''</span>
  
−
The table below has recommended maximum voltage drop values for various circuits. It is important to note that other components in a circuit - terminals, fuses, breakers - add resistance and will increase voltage drop as well, therefore it is important to be conservative.
+
===DC branch circuit example===
 +
All DC branch circuits can be calculated in the same way as this example. This circuit has 3 × 5 W light bulbs.
  
−
'''Note:''' Not all PV systems are wired the same. These voltage drop values are for total circuit length between one component and another. It is common to have DC [[Busbar|busbars]] that have one single set of wires that runs to the [[:Category:Energy storage|energy storage system]] and connect to a positive and negative DC busbar that serve as a point of connection for the [[Inverter|inverter]] and [[Charge controller|charge controller]]. In this case it is necesary to calculate the total voltage drop between the charge controller and the energy storage system, rather than just to the busbar.
+
====Phase 1: Maximum circuit current====
  
−
{| class="wikitable" border=1
+
{| class="wikitable" border=1 style="width: 80%;"
−
!Circuit
+
! style="width: 33%"|Maximum circuit current
−
!Maximum recommended voltage drop
+
! style="text-align:left;"| = Power rating of all DC loads on the circuit ÷ Nominal circuit voltage
 
|-
 
|-
−
|PV source to charge controller
+
|
−
|2%
+
| = (3 × 5 W) ÷ 12 V = 1.25 A
 +
|}
 +
 
 +
====Phase 2: Wire ampacity====
 +
There will only be two current-carrying conductors in the conduit. The maximum indoor temperature 20°C. 75° wet / 90°C dry rated wire will be used for this circuit.
 +
 
 +
The minimum wire size for a circuit can be using the following steps:
 +
<ol>
 +
<li>Determine the ambient temperature correction factor based upon the [[Weather and solar resource evaluation#Maximum ambient temperature|maximum ambient temperature]] using the [[Wire, overcurrent protection, and disconnect sizing and selection#Ambient temperature correction factor table|ambient temperature correction factor table]]. The ambient temperature correction factor for this circuit is 1.11 because it is a 75° wet / 90°C dry rated wire with a maximum indoor temperature of 20°C.
 +
<li>Determine the conduit fill correction factor based upon the number of number of conductors in the conduit using the [[Wire, overcurrent protection, and disconnect sizing and selection#Conduit fill correction factor table|conduit fill correction factor table]] There will only be two current-carrying conductors in the conduit, so the conduit correction fill factor is 1.</li>
 +
<li>Determine the total wire correction parameter based upon the Ambient temperature correction multiplied by the Conduit fill correction factor</li>
 +
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 20%"|Total wire correction parameter
 +
! style="text-align:left;"| = Ambient temperature correction factor × Conduit fill correction factor
 
|-
 
|-
−
|Charge controller to energy storage
+
|
−
|1.5%
+
| = 1.11 × 1 = 1.11
 +
|}
 +
 
 +
<li>Determine minimum wire ampacity. Divide the maximum circuit current (Phase 1) by the total wire correction factor (Step 3)</li>
 +
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 20%"|Minimum wire ampacity
 +
! style="text-align:left;"| = Maximum circuit current (Phase 1) ÷ Total wire correction parameter (Step 3)
 
|-
 
|-
−
|Energy storage to inverter
+
|
−
|1.5%
+
| = 1.25 A ÷ 1.11 = 1.13 A
 +
|}
 +
 
 +
<li>Select a wire size with a maximum rated ampacity equal to or above the minimum wire ampacity calculated in the previous step using the [[Wire, overcurrent protection, and disconnect sizing and selection#Conductor ampacity table|allowable wire ampacity table]]. A 2.5 mm² / 14 AWG, 75° wet / 90°C dry rated wire with an ampacity rating of 20 A will be used for this circuit as this is a commonly used wire type for a circuit of this type. 20 A is larger than the required 1.56 A ampacity.
 +
</li>
 +
</ol>
 +
 
 +
====Phase 3: Overcurrent protection and disconnects====
 +
This circuit does not require an OCPD if the available current is limited by another OCPD or the charge controller - in this case there is both a 15 A OCPD on the connection to the battery and the charge controller itself is current limited to 10 A - to a maximum current that is below the ampacity rating of the wire. It is necessary to check to make sure that the wire will be protected by the other OCPD under the conditions of use.
 +
 
 +
Verify that the nearest OCPD will protect the wire size chosen in Phase 2 from excessive current under the conditions of use. The current rating of the OCPD must be less than the calculated maximum current under conditions of use ''unless'' the calculated maximum current under conditions of use is between standard OCPD values, in this case the next largest OCPD size is used from the [[Wire, overcurrent protection, and disconnect sizing and selection#Phase 3: Overcurrent protection and disconnects|list of standard OCPD sizes]]. If the current rating of the chosen OCPD size is larger than the maximum OCPD size under conditions of use, then the wire size must be increased until it passes this test or an additional OCPD must be added to protect this circuit.
 +
 
 +
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 20%"|Maximum current under conditions of use
 +
! style="text-align:left;"| = [[Wire, overcurrent protection, and disconnect sizing and selection#Conductor ampacity table|Wire ampacity from allowable wire ampacity table]] × Total wire correction parameter (Phase 2).
 
|-
 
|-
−
|DC lighting circuits
+
|
−
|5%
+
| = 20 A × 1.11 = 22.2 A
 +
|}
 +
 
 +
Determine the maximum OCPD size under conditions of use.
 +
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 20%"|Maximum OCPD size under conditions of use
 +
! style="text-align:left;"| = Can be equal to the maximum current under conditions of use. If between standard OCPD sizes, the next largest OCPD is used. Except for the following wire sizes: 15 A maximum for 2.5 mm² / 14 AWG. 20 A maximum for 4 mm² / 12 AWG. 30 A maximum for 6 mm² / 10 AWG.
 
|-
 
|-
−
|DC load circuits
+
|
−
|3%
+
| = 15 A OCPD
 +
|}
 +
 
 +
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 20%"|Verify OCPD under conditions of use
 +
! style="text-align:left;"| = The current rating of the chosen OCPD (Step 2) must be ''less than or equal to'' the maximum OCPD size under conditions of use
 
|-
 
|-
−
|AC load and lighting circuits
+
|
−
|2%
+
| = 15 A OCPD is equal to the maximum 15 A OCPD size
 
|}
 
|}
 +
</ol>
  
−
====Phase 5: Terminal temperature ratings====
+
<span style="color:#FFFFFF; background:#008000">'''No additional OCPD is necessary'''</span>
−
The maximum temperature rating of the any breaker terminals or crimped terminals used in the circuit must be considered. Most terminals are rated for 60°C/75°C or 75°C. 60°C and 90°C terminals are not very common. This information should be printed on the component or be available from the manufacturer or provider. If a wire with a higher temperature rating than that of the terminals in the system, then it must be verified that the OCPD device will still protect the terminals under conditions of use. For example:
 
−
*If the circuit is being sized for use with 90°C rated wire and terminals with 75°C rating - a very common scenario - then the calculations below will have to be performed.
 
−
*If the circuit is being sized for use with 75°C rated wire and terminals with a 75°C rating, then the calculations below do not need to be performed.
 
  
−
The calculation is the same as the calculation performed in Phase 3 of the OCPD sizing entitled - Maximum current under conditions of use - but is instead performed with the ampacity of the chosen wire taken from the column of the [[#Allowable wire ampacities|allowable wire ampacities chart]] at the lower temperature rating of the terminals.
+
====Phase 4: Voltage drop====
 +
If the voltage drop for the wire chosen in Phase 2 for a particular circuit is not within the [[Wire, overcurrent protection, and disconnect sizing and selection#Recommended circuit voltage drop values|recommended values]], then using a larger sized wire should be considered. Increasing the wire size will not affect any other part of this process; the calculated OCPD size can remain the same.
 +
 
 +
This circuit will be 8m meters long one-way. It is 2.5 mm² / 14 AWG, wire with a resistance value in (Ω/Km) of 10.7 Ω. It is recommended that the voltage drop between the charge controller be kept below 5% for any lights and below 3% for any loads. The circuit current is operating current and voltage of the charge controller output. Current is total current required by all of the loads on the circuit (same as calculated in Phase 1). Operating voltage is nominal voltage of the system: 12 V.
  
−
====Step 1: Maximum current considering terminal temperature rating====
 
 
{| class="wikitable" border=1 style="width: 80%;"
 
{| class="wikitable" border=1 style="width: 80%;"
−
! style="width: 33%"|Maximum current considering terminal temperature rating
+
! style="width: 20%"|Voltage drop
−
! style="text-align:left;"| = Wire size (Phase 2) ampacity at terminal temperature rating from [[#Allowable wire ampacities|allowable wire ampacities table]] × Total wire correction parameter (Phase 2).
+
! style="text-align:left;"| = 2 x Circuit current x One-way circuit length (m) x  [[Wire, overcurrent protection, and disconnect sizing and selection#Wire resistance values|Resistance (Ω/Km)]] ÷ 1000
 +
|-
 +
|
 +
| = 2 × 1.25 A × 8m × 10.7 Ω ÷ 1000 = .21 V
 
|}
 
|}
  
−
====Step 2: Verify OCPD protection considering terminal temperature rating====
 
 
{| class="wikitable" border=1 style="width: 80%;"
 
{| class="wikitable" border=1 style="width: 80%;"
−
! style="width: 33%"|Verify OCPD size and derated wire ampacity under conditions of use including terminal temperature rating
+
! style="width: 20%"|Percentage voltage drop
−
! style="text-align:left;"| = Maximum current considering terminal temperature rating (Step 1) must be greater than Chosen OCPD size (Phase 3)
+
! style="text-align:left;"| = Voltage drop ÷ Circuit operating voltage x 100
 +
|-
 +
|
 +
| = .09 V ÷ 12 V × 100 = 1.75%
 
|}
 
|}
  
−
If the wire is not protected by the OCPD at the temperature rating of the terminals in the circuit, then the wire size must be increased until the circuit passes this test. No other calculations need to be performed again. Increasing the wire size will have the added benefit of reducing voltage drop.
+
<span style="color:#FFFFFF; background:#008000">'''1.75% voltage drop for this circuit is acceptable. The combined voltage drop of this circuit and the charge controller load circuit voltage drop is 1.88%, which is less than the recommended maximum of 3%. The wire size is okay.'''</span>
 +
 
 +
==Design summary==
 +
[[File:DConlysystem210204.png|thumb|A three-line wiring diagram for this system.]]
 +
*'''DC nominal voltage:''' 12 V
 +
*'''Mounting system:''' Pole mount
 +
*'''Tilt angle:''' 14°
 +
*'''Azimuth:''' 0°
 +
===Components===
 +
*'''PV module:''' Dasol WDS-A18-80 36-cell polycrystaline module [http://www.opensourcesolar.org/w/downloads/specsheets/DSA1880-11340767037.pdf Specifications sheet]
 +
*'''Charge controller:''' Morningstar SHS-10 PWM charge controller [http://www.opensourcesolar.org/w/downloads/specsheets/SHS_ENG_R2_1_12lowres.pdf Specifications sheet] [http://www.opensourcesolar.org/w/downloads/specsheets/SHSmanualTranslated.pdf Multi-lingual user manual]
 +
*'''Energy storage system:''' MK 8A22NF-DEKA 12V, 55Ah AGM battery [http://www.opensourcesolar.org/w/downloads/specsheets/8A22NF-DEKA_Spec_Sheet.pdf Specifications sheet]
 +
===Circuits===
 +
*'''PV source circuit:''' 4 mm² / 12 AWG, 90°C PV wire. 10 A breaker as a power source disconnect.
 +
*'''Charge controller output circuit/energy storage circuit:''' 4 mm² / 12 AWG, 75° wet / 90°C dry rated wire. 15 A breaker as a power source disconnect.
 +
*'''Charge controller load circuit:''' 4 mm² / 12 AWG, 75° wet / 90°C dry rated wire. No overcurrent protection device required.
 +
*'''DC branch circuit:''' 2.5 mm² / 14 AWG, 75° wet / 90°C dry rated wire. No overcurrent protection device required.
 +
===Grounding system===
 +
*'''Grounding system:''' No grounding system due to cost and the simplicity of the system.
  
 
==Notes/references==
 
==Notes/references==
 
<references/>
 
<references/>

Latest revision as of 12:20, 12 February 2021

Physical evaluation

Location: Pampachiri, Apurimac, Peru
GPS coordinates: -14.1870656, -73.5445298
Altitude: 3378 m
Description: A two story adobe home in the Peruvian Andes with only DC power needs. The home is used all year and the loads are used consistently throughout the year. Load usage is primarily during the evening/night. The homeowners do not intend on adding any major appliances in the near future.

  • Photo of the home.

  • Location of the home.

Contents

Load evaluation

Step 1: Fill out DC load chart

April - September October - March
# Load Quantity Watts Total watts Duty cycle Hours per day Days per week Average daily DC watt-hours Hours per day Days per week Average daily DC watt-hours
1 LED light 6 5 W 30 W 1 3 hours 7 days 90 Wh 3 hours 7 days 90 Wh
2 Radio 1 6 W 6 W 1 5 hours 7 days 30 Wh 5 hours 7 days 30 Wh
3 Cell phone 2 10 W 20 W 1 1 hours 7 days 20 Wh 1 hours 7 days 20 Wh
  • Load: The make and model or type of load.
  • Quantity: The number of the particular load.
  • Watts: The power rating in watts of the load.
  • Total watts = Quantity × Watts
  • Duty cycle = Rated or estimated duty cycle for the load. If the load has no duty cycle a value of 1 should be used. A load with a duty cycle of 20% would be inputted as .2
  • Hours per day: The maximum number of hours the load(s) will be operated per day. If the load has a duty cycle 24 hours should be used.
  • Days per week: The maximum number of days the load(s) will be operated per week.
  • Average daily DC watt-hours = Total watts × Duty cycle × Hours per day × Days per week ÷ 7 days

Step 2: Determine DC energy demand

Total average daily DC watt-hours (April - September) = sum of Average daily DC watt-hours for all loads for April - September
= 140 Wh
Total average daily DC watt-hours (October - March) = sum of Average daily DC watt-hours for all loads for October - March
= 140 Wh

Total average daily energy demand

The total energy demand for the system is the added Average daily DC-watt hours and Average daily AC watt-hours for each time period.

Average daily watt-hours required (April - September) = Total average daily DC watt-hours (April - October) + Total average daily AC watt-hours (April - September)
= 140 Wh
Average daily watt-hours required (April - September) = Total average daily DC watt-hours (October - March) + Total average daily AC watt-hours (October - March)
= 140 Wh

Weather and solar resource evaluation

Maximum ambient temperature = 23°C
Minimum ambient temperature = 2°C
Maximum indoor temperature = 20°C
Minimum indoor temperature = 10°C

  • Retrieving PVGIS monthly insolation data.

  • Retrieving PVGIS monthly insolation data.

  • Retrieving PVGIS weather data.

  • Retrieving PVGIS weather data.

Load and solar resource comparison

Step 1: Determine monthly ratio of energy demand to solar resource

Month Average monthly insolation Total average daily energy demand Ratio
January 193.85 kWh/m² 140 Wh .722
February 162.2 kWh/m² 140 Wh .86
March 179.81 kWh/m² 140 Wh .78
April 174.98 kWh/m² 140 Wh .8
May 214.31 kWh/m² 140 Wh .65
June 200.05 kWh/m² 140 Wh .7
July 210.35 kWh/m² 140 Wh .67
August 229.96 kWh/m² 140 Wh .61
September 126.87 kWh/m² 140 Wh 1.1
October 214.82 kWh/m² 140 Wh .65
November 212.91 kWh/m² 140 Wh .66
December 176.98 kWh/m² 140 Wh .79

Step 2: Determine design values

Design daily insolation = Average monthly insolation from month with the highest ratio ÷ 30
= 126.87 kWh/m² ÷ 30 = 4.23 kWh/m²
Design daily watt-hours required = Total average daily energy demand from month with the highest ratio
= 140 Wh

Design parameters

DC system voltage = 12 V

  • The system, based upon the load evaluation, will be relatively small. A 12 V system makes the most sense.

Irradiance safety parameter = 1.25

  • The irradiance safety parameter is always the same.

Continuous duty safety parameter = 1.25

  • The continuous duty safety parameter is always the same.

Low voltage disconnect parameter = 11.5 V

  • A simple charge controller with a pre-programmed low voltage disconnect will be used.

Energy storage sizing and selection

Step 1: Determine depth of discharge parameter
For this project a depth of discharge of .4 (40%) is a good compromise.

  • Depth of discharge = .4

Step 2: Determine days of autonomy parameter
The home is used daily and providing lighting is very important, but at the same time the budget for the project is limited. The users are willing to adjust their consumption during periods of poor weather according to the state of charge of the energy storage system.

  • Days of autonomy = 2

Step 3: Determine battery temperature correction factor
The minimum indoor temperature was determined to be 10°C. An AGM battery will be used to avoid regular maintenance.

  • Battery temperature correction factor = 1.08

Correction factors for various battery types:[1]

Temperature FLA AGM Gel
25°C 1.00 1.00 1.00
20°C 1.06 1.03 1.04
15°C 1.13 1.05 1.07
10°C 1.19 1.08 1.11
5°C 1.29 1.14 1.18
0°C 1.39 1.20 1.25
-5°C 1.55 1.28 1.34
-10°C 1.70 1.35 1.42

Step 4: Calculate total Ah required

Total Ah required = Average daily Watt-hours required ÷ DC system voltage × Battery temperature correction factor (Step 3) × Days of autonomy parameter (Step 2) ÷ Depth of discharge parameter (Step 1)
= 140 Wh ÷ 12 V × 1.08 × 2 days ÷ .4 = 43 Ah

One MK Deka 12V 55 Ah AGM battery will provide enough storage capacity. Specifications sheet

Specifications:
  • Battery type: AGM
  • Nominal voltage: 12 V
  • C/20 rated capacity: 55 Ah

Step 5: Calculate number of batteries in series

Batteries in series = DC system voltage ÷ Chosen battery voltage
= 12 V ÷ 12 V
= 1 battery

Step 6: Calculate number of parallel battery circuits

Parallel battery circuits = Total Ah required (Step 4) ÷ Chosen battery Ah rating
= 43 Ah ÷ 55 Ah = .78
= Round up to 1 parallel battery circuit (1 battery)

Step 7: Calculate final Ah capacity

Final Ah capacity = Parallel battery circuit (Step 6) × Chosen battery Ah rating
= 1 parallel battery circuit × 55 Ah = 55Ah

Minimum PV source size

Step 1: Deteremine PV source loss parameters

The PV module(s) will be mounted on a pole mount system.

  • Module degradation parameter = .94
  • Shading loss parameter = .95
  • Soiling loss parameter = .97
  • Wiring loss parameter = .96
  • Module mismatch parameter = 1
  • Mounting system temperature adder = 20°C for a pole mount
  • Temperature coefficient of max power %/°C = -.48%/°C
PV source temperature loss parameter = 1 + (Maximum ambient temperature + Mounting system temperature adder - 25°C) x Temperature coefficient of max power %/°C ÷ 100
= 1 + (23°C + 20°C - 25°C) x -.48%/°C ÷ 100 = .91
Total PV source loss parameter = Module degradation parameter × Shading loss parameter × Soiling loss parameter × Wiring loss parameter × Module mismatch parameter × PV source temperature loss parameter
= .94 × .95 × .97 × .96 × 1 × .91 = .76

Step 2: Charge controller efficiency parameter

All charge controllers lose a certain percentage of all energy that is produced as heat as it is transferred to the energy storage system and loads. For both PWM and MPPT charge controllers a value of .98 (98% efficient) can be used.

Step 3: Energy storage efficiency parameter

The system will use an AGM battery, which is a VRLA battery.

  • Valve-regulated lead acid (VRLA) battery efficiency = .85 (85% efficient)

Step 4: Deteremine minimum size of the PV source

Minimum PV source size = Design daily watt-hours required ÷ Design daily insolation ÷ Total PV source loss parameter (Step 1) ÷ Charge controller efficiency parameter (Step 2) ÷ Energy storage efficiency parameter (Step 3)
= 140 Wh ÷ 4.23 kWh/m² ÷ .76 ÷ .98 ÷ .85 = 52 W

Step 5: Determine charge controller type

A PWM charge controller is a reliable, low-cost option for a small system like this.

PWM charge controller sizing and selection

Step 1: Determine PV module power rating

The chosen DC system voltage limits the choices of modules and configurations that are possible with a PWM charge controller. A 12 volt system requires 1 × 36-cell module per string. The minimum size was determined to be 52 W.
A Dasol 80 W, 36-cell polycrystalline PV module will be used for the design. Specifications sheet

Module specifications:

  • Power = 80 W
  • Open circuit voltage (Voc) = 22.3 V
  • Short circuit current (Isc) = 4.85 A
  • Max power voltage (Vmp) = 18.0 V
  • Max power current (Imp) = 4.44 A
  • Temperature coefficient of open circuit voltage (TkVoc) = -.36 %/°C
  • Temperature coefficient of max power (TkPmp) = Not available.
PV module power rating = 80 W
Number of modules in series = 1 module

Step 2: Determine proposed module configuration

This calculation will give a minimum number of PV modules - the result should always be rounded up. Different modules sizes and configurations can be explored to find the optimal design.

Minimum number of PV modules = Minimum PV source size ÷ PV module power rating (Step 1)
= 52 W ÷ 80 W = .65
= 1 × 80 W module.
Minimum number of PV source circuits = Minimum number of PV modules ÷ Number of modules in series (Step 1)
= 1 ÷ 1 = 1

Step 3: Verify excess production

Proposed PV source low insolation production = PV module power rating (Step 1) × Minimum number of PV modules (Step 2) × Total PV source loss parameter × Design daily insolation × Charge controller efficiency parameter × Energy storage efficiency parameter
= 80 W × 1 × .76 × 4.23 kWh/m² × .98 × .85 = 214 Wh
Daily excess production in Ah = (Proposed PV source low insolation production - Design daily watt-hours required) ÷ DC system voltage
= (214 Wh - 140 Wh) ÷ 12 volts = 6.2 Ah
Ah used at full depth of discharge = Final Ah capacity × Depth of discharge parameter
= 55Ah × .5 = 27.5 Ah
Time to reach full state of charge = Ah used at full depth of discharge ÷ Daily excess production in Ah
= 27.5 Ah ÷ 6.2 Ah = 4.4 days

The battery will be able to reach full state of charge while using loads in 4.4 days, which is less than the maximum of 7 days. The design is okay.

Step 4: Verify charging current

This system will use an AGM battery, so that charge current from the PV source should be between .05 (5%) and .2 (20%) of its C/20 rating.

It is necessary to check the minimum required charge current against the available charge current from the proposed PV source power rating.

Available charging current = Maximum power current (Imp) × Minimum number of PV source circuits
= 4.4 A × 1 = 4.4 A
Percentage of C/20 rate = Available charging current ÷ Final Ah capacity
= 4.4 A ÷ 55 Ah = .08

The PV source can supply .08 (8%) of the C/20 current rating of the energy storage system, which is more than .05 (5%) and less than .2 (20%). The PV source configuration is okay.

Step 5: Determine final number of PV modules

Determine a final number of modules and a PV source circuit configuration that can meet the requirements of Step 1, Step 2, Step 3, and Step 4.

Final number of PV modules = 1
Final number of PV modules in series = 1
Final number of PV source circuits = 1

Step 6: Total PV source current

This calculation will give a minimum current rating to use as a basis for selecting the charge controller. The Isc rating of the PV module can be found on its specifications sheet.

Total PV source current = Final number of PV source circuits (Step 5) × Isc rating of chosen module (Step 1) × Irradiance safety parameter
= 1 × 4.85 A × 1.25 = 6.1 A

Step 7: Select a charge controller

The final chosen charge controller should:

  1. Function at the DC system voltage.
  2. The charge controller(s) should have a total current rating that is larger than the minimum current rating (Step 6).

A Morningstar SHS-10 PWM charge controller will be used. Specifications sheet Multi-lingual user manual

Specifications:
  • Charge controller type: PWM
  • Nominal output voltage: 12 V
  • Maximum current rating: 10 A

The result of the following equation should always be rounded up.

Number of charge controllers = Total PV source current (Step 6) ÷ Chosen charge controller current rating
= 6.1 A ÷ 10 A = .61 = 1 (round up to 1 charge controller)

Step 8: Determine final PV source power rating

PV source power rating = PV module power rating (Step 1) × Final number of PV modules (Step 5)
= 80 W × 1 = 80 W

Step 9: Verify PV source and charge controller compatability

PWM charge controllers often have a maximum PV source power rating in watts that limits the size of the PV source. Verify that the maximum PV source power rating is greater than the final PV source power rating. If it is not, the charge controller size needs to be increased.

PV source and charge controller compatability = Final PV source power rating must be less than the maximum PV source power rating of the charge controller
= 80 W PV source is less than 170 W maximum input power rating of charge controller

The PV source and charge controller are compatible.

Wire, overcurrent protection, and disconnect sizing and selection

The chosen wire for a circuit must meet the requirements set out in each phase of this process. The wire size must be increased if it fails to meet any of these phases and then the process must be performed again with the new wire size.

PV source circuit

Phase 1: Maximum circuit current

Maximum circuit current = PV module Isc × Irradiance safety parameter
= 4.85 A × 1.25 = 6.1 A

Phase 2: Wire ampacity

There will only be two current-carrying conductors in the conduit. The maximum ambient temperature 23°C. 90°C wet/dry rated PV wire will be used for this circuit.

The minimum wire size for a circuit can be using the following steps:

  1. Determine the ambient temperature correction factor based upon the maximum ambient temperature using the ambient temperature correction factor table. The ambient temperature correction factor for this circuit is 1.05 because it is a 90°C wet/dry rated wire with a maximum ambient temperature of 23°C.
  2. Determine the conduit fill correction factor based upon the number of number of conductors in the conduit using the conduit fill correction factor table There will only be two current-carrying conductors in the conduit, so the conduit correction fill factor is 1.
  3. Determine the total wire correction parameter based upon the smaller of: the Ambient temperature correction multiplied by the Conduit fill correction factor or .8 (a safety factor from the US National Electrical code).
    4. Total wire correction parameter = Smaller of (Ambient temperature correction factor × Conduit fill correction factor) or .8
    = Smaller of (1.05 × 1) or .8 = .8
  4. Determine minimum wire ampacity. Divide the maximum circuit current (Phase 1) by the total wire correction factor (Step 3)
    5. Minimum wire ampacity = Maximum circuit current (Phase 1) ÷ Total wire correction parameter (Step 3)
    = 6.1 A ÷ .8 = 7.6 A
  5. Select a wire size with a maximum rated ampacity equal to or above the minimum wire ampacity calculated in the previous step using the allowable wire ampacity table. A 4 mm² / 12 AWG, 90°C wet/dry rated PV wire with an ampacity rating of 25 A will be used for this circuit as this is a commonly used wire type for a circuit of this type. 25 A is larger than the required 7.6 A ampacity.

Phase 3: Overcurrent protection and disconnects

This circuit, since it only has 1 PV module, does not require an OCPD, but one will be located near the PV equipment to provide a PV power source disconnect.

The appropriate overcurrent protection device size can be determined by:

  1. Determine the minimum size
    2. Minimum OCPD size = Maximum circuit current (Phase 1) × 1.25
    = 6.1 A × 1.25 = 7.6 A
  2. A standard 10 A DC breaker will be used. This breaker is larger than the required minimum OCPD size and smaller than the rated 25 A ampacity of the wire that it will protect. The PV source is current limited and the wire is sized to handle the maximum current, therefore it is not necessary to verify the OCPD size.

The OCPD size is okay.

Phase 4: Voltage drop

If the voltage drop for the wire chosen in Phase 2 for a particular circuit is not within the recommended values, then using a larger sized wire should be considered. Increasing the wire size will not affect any other part of this process; the calculated OCPD size can remain the same.

This circuit will be 6 meters long one-way. It is 4 mm² / 12 AWG, wire with a resistance value in (Ω/Km) of 6.73 Ω. It is recommended that the voltage drop between the PV source and the charge controller be kept below 3%.

PV source circuit current = Max power current of the PV module
= 4.44 A
PV source circuit nominal voltage = Number of PV modules in series × Max power voltage of the PV module
= 18 V × 1 = 18 V
Voltage drop = 2 x Circuit current x One-way circuit length (m) x Resistance (Ω/Km) ÷ 1000
= 2 × 4.44 A × 6m × 6.73 Ω ÷ 1000 = .36 V
Percentage voltage drop = Voltage drop ÷ nominal circuit voltage x 100
= .36 V ÷ 18 V × 100 = 2%

2% voltage drop for this circuit is acceptable. The wire size is okay.

Charge controller output circuit/battery circuit

This same size wire will be used from the charge controller to the battery with one overcurrent protection device which will also serve as a power source disconnect.

Phase 1: Maximum circuit current

Maximum circuit current = Current rating of the charge controller
= 10 A

Phase 2: Wire ampacity

There will only be two current-carrying conductors in the conduit. The maximum indoor temperature 20°C. 75° wet / 90°C dry rated wire will be used for this circuit.

The minimum wire size for a circuit can be using the following steps:

  1. Determine the ambient temperature correction factor based upon the maximum ambient temperature using the ambient temperature correction factor table. The ambient temperature correction factor for this circuit is 1.11 because it is a 75° wet / 90°C dry rated wire with a maximum indoor temperature of 20°C.
  2. Determine the conduit fill correction factor based upon the number of number of conductors in the conduit using the conduit fill correction factor table There will only be two current-carrying conductors in the conduit, so the conduit correction fill factor is 1.
  3. Determine the total wire correction parameter based upon the Ambient temperature correction multiplied by the Conduit fill correction factor
    4. Total wire correction parameter = Ambient temperature correction factor × Conduit fill correction factor
    = 1.11 × 1 = 1.11
  4. Determine minimum wire ampacity. Divide the maximum circuit current (Phase 1) by the total wire correction factor (Step 3)
    5. Minimum wire ampacity = Maximum circuit current (Phase 1) ÷ Total wire correction parameter (Step 3)
    = 10 A ÷ 1.11 = 9.0 A
  5. Select a wire size with a maximum rated ampacity equal to or above the minimum wire ampacity calculated in the previous step using the allowable wire ampacity table. A 4 mm² / 12 AWG, 75° wet / 90°C dry rated wire with an ampacity rating of 25 A will be used for this circuit as this is a commonly used wire type for a circuit of this type. 25 A is larger than the required 9.0 A ampacity.

Phase 3: Overcurrent protection and disconnects

This circuit requires an OCPD/disconnect as it is connected directly to the battery which is a power source. An OCPD size should be chosen from the list of standard OCPD sizes. If the current rating of the chosen OCPD size is larger than the maximum OCPD size under conditions of use, then the wire size must be increased the next size.

The appropriate overcurrent protection device size can be determined by:

  1. Determine the minimum size
    2. Minimum OCPD size = Maximum circuit current (Phase 1) × 1.25
    = 10 A × 1.25 = 12.5 A
  2. A standard 15 A DC breaker will be used. This breaker is larger than the required minimum OCPD size, but smaller than the 25 A rated ampacity of the wire that it will protect.
  3. Verify that the chosen OCPD size from Step 2 will protect the wire size chosen in Phase 2 from excessive current under the conditions of use. The current rating of the chosen OCPD size (Step 2) must be less than the calculated maximum current under conditions of use unless the calculated maximum current under conditions of use is between standard OCPD values, in this case the next largest OCPD size is used from the list of standard OCPD sizes. If the current rating of the chosen OCPD size is larger than the maximum OCPD size under conditions of use, then the wire size must be increased until it passes this test.
    Maximum current under conditions of use = Wire ampacity from allowable wire ampacity table × Total wire correction parameter (Phase 2).
    = 25 A × 1.11 = 27.75 A

    Determine the maximum OCPD size under conditions of use.

    Maximum OCPD size under conditions of use = Can be equal to the maximum current under conditions of use. If between standard OCPD sizes, the next largest OCPD is used. Except for the following wire sizes: 15 A maximum for 2.5 mm² / 14 AWG. 20 A maximum for 4 mm² / 12 AWG. 30 A maximum for 6 mm² / 10 AWG.
    = 20 A OCPD
    Verify OCPD under conditions of use = The current rating of the chosen OCPD (Step 2) must be less than or equal to the maximum OCPD size under conditions of use
    = 15 A OCPD is less than 20 A OCPD maximum size

The OCPD and wire size are okay.

Phase 4: Voltage drop

If the voltage drop for the wire chosen in Phase 2 for a particular circuit is not within the recommended values, then using a larger sized wire should be considered. Increasing the wire size will not affect any other part of this process; the calculated OCPD size can remain the same.

This circuit will be 1.5 meters long one-way. It is 4 mm² / 12 AWG, wire with a resistance value in (Ω/Km) of 6.73 Ω. It is recommended that the voltage drop between the charge controller and the energy storage system be kept below 1.5%. The circuit current is the Imp of the PV module: 4.44 A. The nominal circuit voltage is the DC system voltage: 12 V.

Voltage drop = 2 x Circuit current x One-way circuit length (m) x Resistance (Ω/Km) ÷ 1000
= 2 × 4.44 A × 1.5m × 6.73 Ω ÷ 1000 = .09 V
Percentage voltage drop = Voltage drop ÷ Nominal circuit voltage voltage x 100
= .09 V ÷ 12 V × 100 = .75%

.75% voltage drop for this circuit is acceptable. The wire size is okay.

Charge controller load circuit

Phase 1: Maximum circuit current

Maximum circuit current = Current rating of the charge controller lighting/load circuit
= 10 A

Phase 2: Wire ampacity

There will only be two current-carrying conductors in the conduit. The maximum indoor temperature 20°C. 75° wet / 90°C dry rated wire will be used for this circuit.

The minimum wire size for a circuit can be using the following steps:

  1. Determine the ambient temperature correction factor based upon the maximum ambient temperature using the ambient temperature correction factor table. The ambient temperature correction factor for this circuit is 1.11 because it is a 75° wet / 90°C dry rated wire with a maximum indoor temperature of 20°C.
  2. Determine the conduit fill correction factor based upon the number of number of conductors in the conduit using the conduit fill correction factor table There will only be two current-carrying conductors in the conduit, so the conduit correction fill factor is 1.
  3. Determine the total wire correction parameter based upon the Ambient temperature correction multiplied by the Conduit fill correction factor
    4. Total wire correction parameter = Ambient temperature correction factor × Conduit fill correction factor
    = 1.11 × 1 = 1.11
  4. Determine minimum wire ampacity. Divide the maximum circuit current (Phase 1) by the total wire correction factor (Step 3)
    5. Minimum wire ampacity = Maximum circuit current (Phase 1) ÷ Total wire correction parameter (Step 3)
    = 10 A ÷ 1.11 = 9.0 A
  5. Select a wire size with a maximum rated ampacity equal to or above the minimum wire ampacity calculated in the previous step using the allowable wire ampacity table. A 4 mm² / 12 AWG, 75° wet / 90°C dry rated wire with an ampacity rating of 25 A will be used for this circuit as this is a commonly used wire type for a circuit of this type. 25 A is larger than the required 9.0 A ampacity.

Phase 3: Overcurrent protection and disconnects

This circuit does not require an OCPD if the available current is limited by another OCPD or the charge controller - in this case there is both a 15 A OCPD on the connection to the battery and the charge controller itself is current limited to 10 A - to a maximum current that is below the ampacity rating of the wire. It is necessary to check to make sure that the wire will be protected by the other OCPD under the conditions of use.

Verify that the nearest OCPD will protect the wire size chosen in Phase 2 from excessive current under the conditions of use. The current rating of the OCPD must be less than the calculated maximum current under conditions of use unless the calculated maximum current under conditions of use is between standard OCPD values, in this case the next largest OCPD size is used from the list of standard OCPD sizes. If the current rating of the chosen OCPD size is larger than the maximum OCPD size under conditions of use, then the wire size must be increased until it passes this test or an additional OCPD must be added to protect this circuit.

Maximum current under conditions of use = Wire ampacity from allowable wire ampacity table × Total wire correction parameter (Phase 2).
= 25 A × 1.11 = 27.8 A

Determine the maximum OCPD size under conditions of use.

Maximum OCPD size under conditions of use = Can be equal to the maximum current under conditions of use. If between standard OCPD sizes, the next largest OCPD is used. Except for the following wire sizes: 15 A maximum for 2.5 mm² / 14 AWG. 20 A maximum for 4 mm² / 12 AWG. 30 A maximum for 6 mm² / 10 AWG.
= 20 A OCPD
Verify OCPD under conditions of use = The current rating of the chosen OCPD (Step 2) must be less than or equal to the maximum OCPD size under conditions of use
= 15 A OCPD is less than the maximum 20 A OCPD size

No additional OCPD is necessary

Phase 4: Voltage drop

If the voltage drop for the wire chosen in Phase 2 for a particular circuit is not within the recommended values, then using a larger sized wire should be considered. Increasing the wire size will not affect any other part of this process; the calculated OCPD size can remain the same.

This circuit will be .25 meters long one-way. It is 4 mm² / 12 AWG, wire with a resistance value in (Ω/Km) of 6.73 Ω. It is recommended that the voltage drop between the charge controller be kept below 5% for any lights and below 3% for any loads. The circuit current is the current required by The circuit nominal voltage is the Nominal circuit voltage is the DC system voltage: 12 V.

Charge controller load circuit current = Power rating of all DC loads ÷ Nominal circuit voltage
= 56 W ÷ 12 V = 4.67 A
Voltage drop = 2 x Circuit current x One-way circuit length (m) x Resistance (Ω/Km) ÷ 1000
= 2 × 4.67 A × .25m × 6.73 Ω ÷ 1000 = .016 V
Percentage voltage drop = Voltage drop ÷ Nominal circuit voltage x 100
= .016 V ÷ 12 V × 100 = .13%

.13% voltage drop for this circuit is acceptable. The wire size is okay.

DC branch circuit example

All DC branch circuits can be calculated in the same way as this example. This circuit has 3 × 5 W light bulbs.

Phase 1: Maximum circuit current

Maximum circuit current = Power rating of all DC loads on the circuit ÷ Nominal circuit voltage
= (3 × 5 W) ÷ 12 V = 1.25 A

Phase 2: Wire ampacity

There will only be two current-carrying conductors in the conduit. The maximum indoor temperature 20°C. 75° wet / 90°C dry rated wire will be used for this circuit.

The minimum wire size for a circuit can be using the following steps:

  1. Determine the ambient temperature correction factor based upon the maximum ambient temperature using the ambient temperature correction factor table. The ambient temperature correction factor for this circuit is 1.11 because it is a 75° wet / 90°C dry rated wire with a maximum indoor temperature of 20°C.
  2. Determine the conduit fill correction factor based upon the number of number of conductors in the conduit using the conduit fill correction factor table There will only be two current-carrying conductors in the conduit, so the conduit correction fill factor is 1.
  3. Determine the total wire correction parameter based upon the Ambient temperature correction multiplied by the Conduit fill correction factor
    4. Total wire correction parameter = Ambient temperature correction factor × Conduit fill correction factor
    = 1.11 × 1 = 1.11
  4. Determine minimum wire ampacity. Divide the maximum circuit current (Phase 1) by the total wire correction factor (Step 3)
    5. Minimum wire ampacity = Maximum circuit current (Phase 1) ÷ Total wire correction parameter (Step 3)
    = 1.25 A ÷ 1.11 = 1.13 A
  5. Select a wire size with a maximum rated ampacity equal to or above the minimum wire ampacity calculated in the previous step using the allowable wire ampacity table. A 2.5 mm² / 14 AWG, 75° wet / 90°C dry rated wire with an ampacity rating of 20 A will be used for this circuit as this is a commonly used wire type for a circuit of this type. 20 A is larger than the required 1.56 A ampacity.

Phase 3: Overcurrent protection and disconnects

This circuit does not require an OCPD if the available current is limited by another OCPD or the charge controller - in this case there is both a 15 A OCPD on the connection to the battery and the charge controller itself is current limited to 10 A - to a maximum current that is below the ampacity rating of the wire. It is necessary to check to make sure that the wire will be protected by the other OCPD under the conditions of use.

Verify that the nearest OCPD will protect the wire size chosen in Phase 2 from excessive current under the conditions of use. The current rating of the OCPD must be less than the calculated maximum current under conditions of use unless the calculated maximum current under conditions of use is between standard OCPD values, in this case the next largest OCPD size is used from the list of standard OCPD sizes. If the current rating of the chosen OCPD size is larger than the maximum OCPD size under conditions of use, then the wire size must be increased until it passes this test or an additional OCPD must be added to protect this circuit.

Maximum current under conditions of use = Wire ampacity from allowable wire ampacity table × Total wire correction parameter (Phase 2).
= 20 A × 1.11 = 22.2 A

Determine the maximum OCPD size under conditions of use.

Maximum OCPD size under conditions of use = Can be equal to the maximum current under conditions of use. If between standard OCPD sizes, the next largest OCPD is used. Except for the following wire sizes: 15 A maximum for 2.5 mm² / 14 AWG. 20 A maximum for 4 mm² / 12 AWG. 30 A maximum for 6 mm² / 10 AWG.
= 15 A OCPD
Verify OCPD under conditions of use = The current rating of the chosen OCPD (Step 2) must be less than or equal to the maximum OCPD size under conditions of use
= 15 A OCPD is equal to the maximum 15 A OCPD size

No additional OCPD is necessary

Phase 4: Voltage drop

If the voltage drop for the wire chosen in Phase 2 for a particular circuit is not within the recommended values, then using a larger sized wire should be considered. Increasing the wire size will not affect any other part of this process; the calculated OCPD size can remain the same.

This circuit will be 8m meters long one-way. It is 2.5 mm² / 14 AWG, wire with a resistance value in (Ω/Km) of 10.7 Ω. It is recommended that the voltage drop between the charge controller be kept below 5% for any lights and below 3% for any loads. The circuit current is operating current and voltage of the charge controller output. Current is total current required by all of the loads on the circuit (same as calculated in Phase 1). Operating voltage is nominal voltage of the system: 12 V.

Voltage drop = 2 x Circuit current x One-way circuit length (m) x Resistance (Ω/Km) ÷ 1000
= 2 × 1.25 A × 8m × 10.7 Ω ÷ 1000 = .21 V
Percentage voltage drop = Voltage drop ÷ Circuit operating voltage x 100
= .09 V ÷ 12 V × 100 = 1.75%

1.75% voltage drop for this circuit is acceptable. The combined voltage drop of this circuit and the charge controller load circuit voltage drop is 1.88%, which is less than the recommended maximum of 3%. The wire size is okay.

Design summary

A three-line wiring diagram for this system.
  • DC nominal voltage: 12 V
  • Mounting system: Pole mount
  • Tilt angle: 14°
  • Azimuth: 0°

Components

Circuits

  • PV source circuit: 4 mm² / 12 AWG, 90°C PV wire. 10 A breaker as a power source disconnect.
  • Charge controller output circuit/energy storage circuit: 4 mm² / 12 AWG, 75° wet / 90°C dry rated wire. 15 A breaker as a power source disconnect.
  • Charge controller load circuit: 4 mm² / 12 AWG, 75° wet / 90°C dry rated wire. No overcurrent protection device required.
  • DC branch circuit: 2.5 mm² / 14 AWG, 75° wet / 90°C dry rated wire. No overcurrent protection device required.

Grounding system

  • Grounding system: No grounding system due to cost and the simplicity of the system.

Notes/references

  1. ↑ Trojan Battery Company - Battery Sizing Guidelines https://www.trojanbattery.com/pdf/TRJN0168_BattSizeGuideFL.pdf
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