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)
 
|-
 
|-
 
|
 
|
Line 314: Line 312:
 
|}
 
|}
  
−
'''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%"|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|Design 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]]
 
|-
 
|-
 
|
 
|
Line 497: Line 501:
 
|}
 
|}
  
−
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 23°C. 90°C rated PV wire will be used for this circuit.
+
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:
 
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]] 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 1.08 because it is a 90°C rated wire with a maximum ambient temperature of 23°C.
+
<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 fill correction factor based upon the number of number of conductors in the conduit using the [[Wire, overcurrent protection, and disconnect sizing and selection#Ambient temperature 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 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 fill  correction 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%;"
Line 579: Line 602:
 
|-
 
|-
 
|
 
|
−
| = Smaller of (1.04 × 1) or .8 = .8
+
| = Smaller of (1.05 × 1) or .8 = .8
 
|}
 
|}
  
Line 591: Line 614:
 
|}
 
|}
  
−
<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#Allowable wire ampacity table|allowable wire ampacity table]]. A 4 mm² PV wire with an ampacity rating of 30 A at 90°C will be used for this circuit as this is a commonly used wire type and size for a circuit of this type. 30 A provides far more ampacity than the required 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 [[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>
Line 609: Line 632:
 
|-
 
|-
 
|
 
|
−
| = 7.6 A × 1.25 = 9.5 A
+
| = 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
 +
|-
 +
|
 +
| = 4.44 A
 
|}
 
|}
−
<li>A standard 10 A DC breaker will be used. This is breaker is larger than the required minimum OCPD size, but far smaller than the rated ampacity of the wire that it will protect.</li>
 
  
−
<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.
+
{| 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
 +
|-
 +
|
 +
| = 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
 +
|-
 +
|
 +
| = 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
 +
|-
 +
|
 +
| = .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
 +
|-
 +
|
 +
| = 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
 +
|}
 +
 
 +
<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:
 +
 
 +
<ol>
 +
<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
 +
|-
 +
|
 +
| = 10 A × 1.25 = 12.5 A
 +
|}
 +
<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>
 +
 
 +
<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.
  
 
{| 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%"|Maximum current under conditions of use
−
! style="text-align:left;"| = [[#Allowable wire ampacities|Wire ampacity from allowable wire ampacity table]] × Total wire correction parameter (Phase 2).
+
! 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
 +
|}
 +
 
 +
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.
 
|-
 
|-
 
|
 
|
−
| = 30 A × .8 = 24 A
+
| = 20 A OCPD
 
|}
 
|}
  
 
{| class="wikitable" border=1 style="width: 80%;"
 
{| class="wikitable" border=1 style="width: 80%;"
 
! style="width: 20%"|Verify OCPD under conditions of use
 
! style="width: 20%"|Verify OCPD under conditions of use
−
! style="text-align:left;"| = Maximum current under conditions of use ''must be greater than'' the current rating of the chosen OCPD (Step 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
 
|-
 
|-
 
|
 
|
−
| = 24 A is greater than 10 A.
+
| = 15 A OCPD is less than 20 A OCPD maximum size
 
|}
 
|}
 
</ol>
 
</ol>
  
−
The OCPD size is okay.
+
<span style="color:#FFFFFF; background:#008000">'''The OCPD and wire size are okay.'''</span>
  
 
====Phase 4: Voltage drop====
 
====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.
 
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 wire with a resistance value in (Ω/Km) of 6.73 Ω. We would like to keep the voltage drop between the PV source and the charge controller below 2%. The circuit current is the Imp of the PV module: 4.44 A. The circuit operating voltage is the Vmp of the PV module: 18 V.
+
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%;"
 
{| 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  [[Wire, overcurrent protection, and disconnect sizing and selection|#Wire 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 × 4.44 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
 
|-
 
|-
 
|
 
|
−
| = 2 × 4.44 A × 6m × 6.73 Ω ÷ 1000 = .36 V
+
| = .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
 +
|}
 +
 
 +
<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 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).
 +
|-
 +
|
 +
| = 25 A × 1.11 = 27.8 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.
 +
|-
 +
|
 +
| = 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>
 +
 
 +
<span style="color:#FFFFFF; background:#008000">'''No additional OCPD is necessary'''</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 .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%;"
 +
! 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 × 4.67 A × .25m × 6.73 Ω ÷ 1000 = .016 V
 
|}
 
|}
  
 
{| 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%
 +
|}
 +
 
 +
<span style="color:#FFFFFF; background:#008000">'''.13% voltage drop for this circuit is acceptable. The wire size is okay.'''</span>
 +
 
 +
===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====
 +
 
 +
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 33%"|Maximum circuit current
 +
! style="text-align:left;"| = 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:
 +
<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)
 +
|-
 +
|
 +
| = 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).
 +
|-
 +
|
 +
| = 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.
 +
|-
 +
|
 +
| = 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
 
|-
 
|-
 
|
 
|
−
| = .36 V ÷ 18 V × 100 = 2%
+
| = 15 A OCPD is equal to the maximum 15 A OCPD size
 
|}
 
|}
 +
</ol>
  
−
A 2% voltage drop for this circuit is okay. The wire size is okay.
+
<span style="color:#FFFFFF; background:#008000">'''No additional OCPD is necessary'''</span>
  
−
====Phase 5: Terminal temperature ratings====
+
====Phase 4: Voltage drop====
−
The PV wire is rated at 90°C, but the terminals on the charge controller and breaker are rated at 75°C. It must be verified that the OCPD will still protect these terminals at their lower temperature rating. 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 decreasing 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 ampacity based upon terminal temperature rating====
 
 
{| class="wikitable" border=1 style="width: 80%;"
 
{| class="wikitable" border=1 style="width: 80%;"
−
! style="width: 33%"|Maximum ampacity based upon 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 ampacity 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
 
|-
 
|-
 
|
 
|
−
| = 25 A × .8 = 20 A
+
| = 2 × 1.25 A × 8m × 10.7 Ω ÷ 1000 = .21 V
 
|}
 
|}
  
−
====Step 2: Verify OCPD protection of terminals====
 
 
{| class="wikitable" border=1 style="width: 80%;"
 
{| class="wikitable" border=1 style="width: 80%;"
−
! style="width: 33%"|Verify OCPD protection of terminals
+
! style="width: 20%"|Percentage voltage drop
−
! style="text-align:left;"| = Maximum current considering terminal temperature rating (Step 1) ''must be greater than'' the current rating of the chosen OCPD (Phase 3)
+
! style="text-align:left;"| = Voltage drop ÷ Circuit operating voltage x 100
 
|-
 
|-
 
|
 
|
−
| = 20 A is greater than the the 10 A current rating of the breaker
+
| = .09 V ÷ 12 V × 100 = 1.75%
 
|}
 
|}
  
−
Wire and OCPD size are okay.
+
<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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