Difference between revisions of "Detailed DC system design"

From Open Source Solar Project
Jump to navigation Jump to search
m (Text replacement - "Allowable wire ampacity table" to "Conductor ampacity table")
 
(193 intermediate revisions by the same user not shown)
Line 1: Line 1:
 
[[Category:Design examples]]
 
[[Category:Design examples]]
 +
<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>
Line 10: Line 12:
 
</gallery>
 
</gallery>
  
−
==DC load evaluation==
+
==[[Load evaluation]]==
 +
====Step 1: Fill out DC load chart====
 
{| class="wikitable" style="text-align: center;"
 
{| class="wikitable" style="text-align: center;"
 +
|
 +
|
 +
|
 +
|
 +
|
 +
|
 +
!colspan="3"|April - September
 +
!colspan="3"|October - March
 +
|-
 
!#
 
!#
 
!Load
 
!Load
Line 18: Line 30:
 
!Total watts
 
!Total watts
 
![[Duty cycle]]
 
![[Duty cycle]]
 +
!Hours per day
 +
!Days per week
 +
!Average daily DC watt-hours
 
!Hours per day
 
!Hours per day
 
!Days per week
 
!Days per week
Line 23: Line 38:
 
|-
 
|-
 
|1
 
|1
−
|Cree 5 W LED
+
|LED light
 
|6
 
|6
 
|5 W
 
|5 W
 
|30 W
 
|30 W
 
|1
 
|1
 +
|3 hours
 +
|7 days
 +
|90 Wh
 
|3 hours
 
|3 hours
 
|7 days
 
|7 days
Line 33: Line 51:
 
|-
 
|-
 
|2
 
|2
−
|Retekess radio
+
|Radio
 +
|1
 
|6 W
 
|6 W
−
|1
 
 
|6 W
 
|6 W
 
|1
 
|1
 +
|5 hours
 +
|7 days
 +
|30 Wh
 
|5 hours
 
|5 hours
 
|7 days
 
|7 days
Line 43: Line 64:
 
|-
 
|-
 
|3
 
|3
−
|Samsung cell phone
+
|Cell phone
 
|2
 
|2
 
|10 W
 
|10 W
 
|20 W
 
|20 W
 
|1
 
|1
−
|1 hour
+
|1 hours
 +
|7 days
 +
|20 Wh
 +
|1 hours
 
|7 days
 
|7 days
 
|20 Wh
 
|20 Wh
−
|- style="background-color:#ADD8E6;"
 
−
|colspan="8"|'''Total average daily DC watt-hours'''
 
−
|'''140 Wh'''
 
 
|}
 
|}
 +
 
*'''Load:''' The make and model or type of load.
 
*'''Load:''' The make and model or type of load.
−
*'''Quantity:''' The number of of that particular load.
+
*'''Quantity:''' The number of the particular load.
 
*'''Watts:''' The power rating in watts of the load.
 
*'''Watts:''' The power rating in watts of the load.
 
*'''Total watts =''' Quantity × Watts
 
*'''Total watts =''' Quantity × Watts
Line 63: Line 85:
 
*'''Days per week:''' The maximum number of days the load(s) will be operated per week.  
 
*'''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
 
*'''Average daily DC watt-hours =''' Total watts × Duty cycle × Hours per day × Days per week ÷ 7 days
−
*'''Total average daily DC watt-hours =''' sum of Average daily DC watt-hours for all loads
 
  
−
==Average daily watt-hours required==
+
====Step 2: Determine DC energy demand====
−
{| class="wikitable" border=1
+
 
−
!Average daily watt-hours required
+
{| class="wikitable" border=1 style="width: 80%;"
−
!= Total average daily DC watt-hours + Total average daily AC watt-hours
+
! style="width: 20%"|Total average daily DC watt-hours (April - September)
 +
! style="text-align:left;"| = sum of Average daily DC watt-hours for all loads for April - September
 +
|-
 +
|
 +
| style="text-align:left;"| = 140 Wh
 +
|}
 +
 
 +
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 20%"|Total average daily DC watt-hours (October - March)
 +
! style="text-align:left;"| = sum of Average daily DC watt-hours for all loads for October - March
 +
|-
 +
|
 +
| style="text-align:left;"| = 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.
 +
 
 +
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 20%"|Average daily watt-hours required (April - September)
 +
! style="text-align:left;"| = Total average daily DC watt-hours (April - October) + Total average daily AC watt-hours (April - September)
 +
|-
 +
|
 +
| = 140 Wh
 +
|}
 +
 
 +
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 20%"|Average daily watt-hours required (April - September)
 +
! style="text-align:left;"| =  Total average daily DC watt-hours (October - March) + Total average daily AC watt-hours (October - March)
 
|-
 
|-
−
|Average daily watt-hours required
+
|
−
|= 140 Wh
+
| = 140 Wh
 
|}
 
|}
  
−
==Weather and solar resource evaluation==
+
==[[Weather and solar resource evaluation]]==
 
'''Maximum ambient temperature =''' 23°C<br />
 
'''Maximum ambient temperature =''' 23°C<br />
 
'''Minimum ambient temperature =''' 2°C<br />
 
'''Minimum ambient temperature =''' 2°C<br />
 +
'''Maximum indoor temperature =''' 20°C<br />
 
'''Minimum indoor temperature =''' 10°C<br />
 
'''Minimum indoor temperature =''' 10°C<br />
  
Line 86: Line 136:
 
</gallery>
 
</gallery>
  
−
==Load and solar resource comparison==
+
==[[Load and solar resource comparison]]==
 +
 
 +
====Step 1: Determine monthly ratio of energy demand to solar resource====
  
 
{| class="wikitable" border=1
 
{| class="wikitable" border=1
 
!Month
 
!Month
−
![[Weather and solar resource evaluation#Solar resource (insolation)|Average daily insolation]]
+
![[Weather and solar resource evaluation#Solar resource (insolation)|Average monthly insolation]]
−
![[Load evaluation#Average daily Watt-hours required|Average daily Watt-hours required]]
+
![[Load evaluation#Total average daily energy demand|Total average daily energy demand]]
 
!Ratio
 
!Ratio
 
|-
 
|-
 
|January
 
|January
−
|193.85 kWh/m² / 30 = 6.46 kWh/m²
+
|193.85 kWh/m²
 
|140 Wh
 
|140 Wh
−
|21.67
+
|.722
 
|-
 
|-
 
|February
 
|February
−
|162.2 kWh/m² / 30 = 5.41 kWh/m²
+
|162.2 kWh/m²
 
|140 Wh
 
|140 Wh
−
|25.90
+
|.86
 
|-
 
|-
 
|March
 
|March
−
|(179.81 kWh/m² / 30 = 6.00 kWh/m²
+
|179.81 kWh/m²
 
|140 Wh
 
|140 Wh
−
|23.36
+
|.78
 
|-
 
|-
 
|April
 
|April
−
|174.98 kWh/m² / 30 = 5.83 kWh/m²
+
|174.98 kWh/m²
 
|140 Wh
 
|140 Wh
−
|24.00
+
|.8
 
|-
 
|-
 
|May
 
|May
−
|214.31 kWh/m² / 30 = 7.14 kWh/m²
+
|214.31 kWh/m²
 
|140 Wh
 
|140 Wh
−
|19.60
+
|.65
 
|-
 
|-
 
|June
 
|June
−
|200.05 kWh/m² / 30 = 6.67 kWh/m²
+
|200.05 kWh/m²
 
|140 Wh
 
|140 Wh
−
|20.10
+
|.7
 
|-
 
|-
 
|July
 
|July
−
|210.35 kWh/m² / 30 = 7.01 kWh/m²
+
|210.35 kWh/m²
 
|140 Wh
 
|140 Wh
−
|19.97
+
|.67
 
|-
 
|-
 
|August
 
|August
−
|229.96 kWh/m² / 30 = 7.67 kWh/m²
+
|229.96 kWh/m²
 
|140 Wh
 
|140 Wh
−
|18.26
+
|.61
 
|- style="background-color:#F08080;"
 
|- style="background-color:#F08080;"
 
|September
 
|September
−
|126.87 kWh/m² / 30 = 4.23 kWh/m²
+
|126.87 kWh/m²
 
|140 Wh
 
|140 Wh
−
|33.10
+
|1.1
 
|-
 
|-
 
|October
 
|October
−
|214.82 kWh/m² / 30 = 7.16 kWh/m²
+
|214.82 kWh/m²
 
|140 Wh
 
|140 Wh
−
|19.55
+
|.65
 
|-
 
|-
 
|November
 
|November
−
|212.91 kWh/m² / 30 = 7.10 kWh/m²
+
|212.91 kWh/m²
 
|140 Wh
 
|140 Wh
−
|19.73
+
|.66
 
|-
 
|-
 
|December
 
|December
−
|176.98 kWh/m² / 30 = 5.90 kWh/m²
+
|176.98 kWh/m²
 
|140 Wh
 
|140 Wh
−
|23.73
+
|.79
 
|}
 
|}
 
*'''Month:''' The month of the year.
 
*'''Month:''' The month of the year.
−
*'''Average daily insolation:''' Solar resource data from PVGIS.
+
*'''Average monthly insolation:''' Solar resource data obtained for the location from [[Weather and solar resource evaluation]].
−
*'''Average daily Watt-hours required''' from load evaluation.
+
*'''[[Load evaluation#Total average daily energy demand|Total average daily energy demand]]''' for the month from the load evaluation.
−
*'''Ratio =''' Average daily Watt-hours required ÷ Average daily insolation
+
*'''Ratio =''' Total average daily energy demand ÷ Average monthly insolation
 +
 
 +
====Step 2: Determine design values====
 +
 
 +
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 20%"|Design daily insolation
 +
! style="text-align:left;"| = Average monthly insolation from month with the highest ratio ÷ 30
 +
|-
 +
|
 +
| = 126.87 kWh/m² ÷ 30 = 4.23 kWh/m²
 +
|}
  
−
==Design parameters==
+
{| class="wikitable" border=1 style="width: 80%;"
−
'''System voltage parameter =''' 12 V
+
! style="width: 20%"|Design daily watt-hours required
 +
! style="text-align:left;"| = Total average daily energy demand from month with the highest ratio
 +
|-
 +
|
 +
| = 140 Wh
 +
|}
 +
 
 +
==[[:Category:Design parameters|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.
 
*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
 
*The irradiance safety parameter is always the same.
 
*The irradiance safety parameter is always the same.
−
'''Continuous duty safety parameter =''' 1.25
+
'''[[Continuous duty safety parameter]] =''' 1.25
 
*The continuous duty safety parameter is always the same.
 
*The continuous duty safety parameter is always the same.
−
'''Low voltage disconnect parameter =''' 11.5 V
+
'''[[Low voltage disconnect parameter]] =''' 11.5 V
 
*A simple charge controller with a pre-programmed low voltage disconnect will be used.
 
*A simple charge controller with a pre-programmed low voltage disconnect will be used.
  
−
==Energy storage sizing and selection==
+
==[[Energy storage sizing and selection]]==
−
[[File:Energystorageprocess2011132.png|thumb|right|A flowchart depicting the primary inputs and outputs of the energy storage sizing and selection process.]]
+
'''Step 1: Determine depth of discharge parameter'''<br />
−
The [[Energy storage|energy storage system]] is sized based upon the average daily energy requirements for the system and the design parameters. The first 5 steps of this process output a suggest Ah size for the energy storage system, but then it is necessary to determine a series and parallel configuration based upon the available battery voltages and sizes.
 
−
 
 
−
'''Step 1: Determine depth of discharge parameter'''
 
 
For this project a depth of discharge of .4 (40%) is a good compromise.
 
For this project a depth of discharge of .4 (40%) is a good compromise.
 
*Depth of discharge = .4
 
*Depth of discharge = .4
  
−
'''Step 2: Determine days of autonomy parameter'''
+
'''Step 2: Determine days of autonomy parameter'''<br />
 
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.
 
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
 
*Days of autonomy = 2
  
−
'''Step 3: Determine battery temperature correction factor'''
+
'''Step 3: Determine battery temperature correction factor'''<br />
 
The minimum indoor temperature was determined to be 10°C. An AGM battery will be used to avoid regular maintenance.
 
The minimum indoor temperature was determined to be 10°C. An AGM battery will be used to avoid regular maintenance.
  
Line 198: Line 265:
 
|1.00
 
|1.00
 
|1.00
 
|1.00
 +
|-
 +
|20°C
 +
|1.06
 +
|1.03
 +
|1.04
 +
|-
 +
|15°C
 +
|1.13
 +
|1.05
 +
|1.07
 
|-
 
|-
 
|10°C
 
|10°C
Line 203: Line 280:
 
|1.08
 
|1.08
 
|1.11
 
|1.11
 +
|-
 +
|5°C
 +
|1.29
 +
|1.14
 +
|1.18
 
|-
 
|-
 
|0°C
 
|0°C
Line 208: Line 290:
 
|1.20
 
|1.20
 
|1.25
 
|1.25
 +
|-
 +
| -5°C
 +
|1.55
 +
|1.28
 +
|1.34
 
|-
 
|-
 
| -10°C
 
| -10°C
Line 219: Line 306:
 
{| 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)
 
|-
 
|-
 
|
 
|
−
| style="text-align:left;"| = 140 Wh ÷ 12 V × 1.08 × 2 days ÷ .4 = 63 Ah
+
| style="text-align:left;"| = 140 Wh ÷ 12 V × 1.08 × 2 days ÷ .4 = 43 Ah
−
|-
 
−
|
 
−
| style="text-align:left;"| = 63 Ah
 
 
|}
 
|}
  
−
'''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
 
|-
 
|-
 
|
 
|
Line 238: Line 328:
 
|-
 
|-
 
|
 
|
−
| 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
 
|-
 
|-
 
|
 
|
−
| style="text-align:left;"| = 63 Ah ÷ 75 Ah = .84
+
| style="text-align:left;"| = 43 Ah ÷ 55 Ah = .78
 
|-
 
|-
 
|
 
|
−
| style="text-align:left;"| = Round up to 1 × 75 Ah battery.
+
| style="text-align:left;"| = Round up to 1 parallel battery circuit (1 battery)
 
|}
 
|}
  
Line 257: Line 347:
 
{| 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 × 75 Ah
 
 
|-
 
|-
 
|
 
|
−
| style="text-align:left;"| = 75Ah
+
| style="text-align:left;"| = 1 parallel battery circuit × 55 Ah = 55Ah
 
|}
 
|}
  
−
==Minimum PV source size==
+
==[[Minimum PV source size]]==
−
The size of the [[PV module|PV source]], which is determined based upon the [[Load evaluation|load evaluation]] and [[Weather and solar resource evaluation|weather and solar resource evaluation]] will determine the necessary size of the charge controller. The charge controller must be selected at the same time as the PV source as the [[Charge controller#Charge controller types|charge controller type]] - PWM or MPPT - will also determine the possible configurations of PV modules.
 
−
 
 
−
In this phase of the design process, more than in any other phase, it is necessary to explore different designs using [[PV module|PV module]], [[Series and parallel|series and parallel wiring configurations]], and [[Charge controller|charge controllers]] in order to achieve the highest performance at the lowest cost possible. This phase may have to be performed several times.
 
−
 
 
−
An off-grid PV system that depends upon the PV as its single charging source requires an array that is sufficiently sized to be able to generate sufficient energy to both meet the energy needs of the users and to recharge the [[Energy storage|energy storage system]] under less than ideal conditions. Any sizing decisions should therefore lean towards an oversized PV source.
 
−
 
 
 
====Step 1: Deteremine PV source loss parameters====
 
====Step 1: Deteremine PV source loss parameters====
 
The PV module(s) will be mounted on a pole mount system.
 
The PV module(s) will be mounted on a pole mount system.
Line 280: Line 361:
 
*'''Wiring loss parameter =''' .96
 
*'''Wiring loss parameter =''' .96
 
*'''Module mismatch parameter =''' 1
 
*'''Module mismatch parameter =''' 1
−
*'''PV source temperature loss parameter ='''  -.48%/°C
 
 
*'''Mounting system temperature adder =''' 20°C for a pole mount
 
*'''Mounting system temperature adder =''' 20°C for a pole mount
 +
*'''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
 
|-
 
|-
 
|
 
|
−
| = 1 + (23°C + 20°C - 25°C) x -.48%/°C ÷ 100
+
| = 1 + (23°C + 20°C - 25°C) x -.48%/°C ÷ 100 = .91
−
|-
 
−
|
 
−
| = .91
 
 
|}
 
|}
  
−
::{| 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
 
|-
 
|-
 
|
 
|
−
| = .94 × .95 × .97 × .96 × 1 × .91
+
| = .94 × .95 × .97 × .96 × 1 × .91 = .76
−
|-
 
−
|
 
−
| = .76
 
 
|}
 
|}
  
−
====Step 2: Determine charge controller type====
+
====Step 2: Charge controller efficiency parameter====
−
A [[Charge controller#Pulse width modulation (PWM)|Pulse width modulation (PWM) charge controller]] is an good economical option for a small DC system.
+
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: Charge controller efficiency parameter====
+
====Step 3: Energy storage efficiency parameter====
−
*Pulse width modulation (PWM) charge controller efficiency: .99 (99% efficient)
+
The system will use an [[Lead acid battery#Valve-regulated lead acid (VRLA)|AGM battery]], which is a VRLA battery.
−
 
 
−
====Step 4: Energy storage efficiency parameter====
 
−
The system will use an [[Lead acid batteries#Valve-regulated lead acid (VRLA)|AGM battery]], which is a VRLA battery.
 
 
*Valve-regulated lead acid (VRLA) battery efficiency = .85 (85% efficient)
 
*Valve-regulated lead acid (VRLA) battery efficiency = .85 (85% efficient)
  
−
====Step 5: Deteremine minimum size of the PV source====
+
====Step 4: Deteremine minimum size of the PV source====
 
{| class="wikitable" border=1 style="width: 80%;"
 
{| class="wikitable" border=1 style="width: 80%;"
 
! style="width: 20%"|Minimum PV source size
 
! style="width: 20%"|Minimum PV source size
−
! style="text-align:left;"| = [[Load and solar resource comparison|Average daily Watt-hours required]] ÷ [[Load and solar resource comparison|Design insolation]]   ÷ Total PV source loss parameter (Step 1) ÷ Charge controller efficiency parameter (Step 3) ÷ Energy storage efficiency parameter (Step 4)
+
! style="text-align:left;"| = [[Load and solar resource comparison|Design daily watt-hours required]] ÷ [[Load and solar resource comparison|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 ÷ .99 ÷ .85
 
 
|-
 
|-
 
|
 
|
−
| = 51.75 W
+
| = 140 Wh ÷ 4.23 kWh/m² ÷ .76 ÷ .98 ÷ .85  = 52 W
 
|}
 
|}
  
−
==PWM charge controller sizing and selection==
+
====Step 5: Determine charge controller type====
−
This system will use a PWM charge controller. The charge controller and PV source must be sized together.
+
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====
 
====Step 1: Determine PV module power rating====
−
This system will use 1 × 36-cell module per string. The minimum size was determined to be 51.75 W. We will proceed with an
+
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%;"
 +
! style="width: 20%"|PV module power rating
 +
! style="text-align:left;"| = 80 W
 +
|}
 +
 
 +
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 20%"|Number of modules in series
 +
! style="text-align:left;"| = 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.
  
−
====Step 2: Determine proposed number of PV modules====
 
−
This calculation will give a ''minimum'' number of PV modules. Different modules sizes and configurations can be explored to find the optimal design.
 
 
{| class="wikitable" border=1 style="width: 80%;"
 
{| class="wikitable" border=1 style="width: 80%;"
 
! style="width: 20%"|Minimum number of PV modules
 
! style="width: 20%"|Minimum number of PV modules
 
! style="text-align:left;"| = [[Minimum PV source size|Minimum PV source size]] ÷ PV module power rating (Step 1)
 
! style="text-align:left;"| = [[Minimum PV source size|Minimum PV source size]] ÷ PV module power rating (Step 1)
 +
|-
 +
|
 +
| = 52 W ÷ 80 W = .65
 +
|-
 +
|
 +
| = 1 × 80 W module.
 
|}
 
|}
  
−
::The final number of PV modules should always be larger than this value, thus if the the result of the calculation is a decimal, it should be rounded up.
+
{| class="wikitable" border=1 style="width: 80%;"
 +
! 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)
 +
|-
 +
|
 +
| = 1 ÷ 1 = 1
 +
|}
  
 
====Step 3: Verify excess production====
 
====Step 3: Verify excess production====
−
 
 
{| 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;"| = 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 3: 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]]
 +
|-
 +
|
 +
| = 80 W × 1 × .76 × 4.23 kWh/m² × .98 × .85 = 214 Wh
 
|}
 
|}
  
 
{| 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]]
 +
|-
 +
|
 +
| = (214 Wh - 140 Wh) ÷ 12 volts = 6.2 Ah
 
|}
 
|}
  
 
{| 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]]
 +
|-
 +
|
 +
| = 55Ah × .5 = 27.5 Ah
 
|}
 
|}
  
Line 362: Line 473:
 
! style="width: 20%"|Time to reach full state of charge
 
! style="width: 20%"|Time to reach full state of charge
 
! style="text-align:left;"| = Ah used at full depth of discharge ÷ Daily excess production in Ah
 
! style="text-align:left;"| = Ah used at full depth of discharge ÷ Daily excess production in Ah
 +
|-
 +
|
 +
| = 27.5 Ah ÷ 6.2 Ah = 4.4 days
 
|}
 
|}
  
−
If the time to reach full state of charge is less than 7 days, then the size of the PV source should be increased until it is below 7 days.
+
<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====
−
Lead acid batteries last longer and perform better when they are regularly recharged with a current in a certain range - typically between .05-.13 (5-13%) of their C/20 rating.<ref name="trojanpaper"> Trojan Battery Company - User's Guide https://www.trojanbattery.com/pdf/TrojanBattery_UsersGuide.pdf</ref> If a system uses many loads during the day, this will limit the available charging current for the energy storage system and should be taken into account by increasing the PV source size. The maximum charging current for most lead acid batteries is between .13 (13%) and .2 (20%) of the C/20 rate.<ref name="rollspaper">Rolls Battery - Battery User Manual https://rollsbattery.com/public/docs/user_manual/Rolls_Battery_Manual.pdf</ref> Most designs should have a charge rate between 5-10% - closer to 10% if the system is used heavily during the day. It is necessary to consult the manual or manufacturer for recommended maximum and minimum charging currents.  
+
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
 
−
|}
 
  
 
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.
Line 378: Line 487:
 
{| 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 (Step 2) × [[Minimum PV source size#Step 3: Charge controller efficiency parameter|Charge controller efficiency parameter]] × [[Minimum PV source size#Step 1: Deteremine PV source loss parameters|Module degradation parameter]] × [[Minimum PV source size#Step 1: Deteremine PV source loss parameters|Soiling loss parameter]]
+
! style="text-align:left;"| = [[PV module#Standard test conditions|Maximum power current (Imp)]] × Minimum number of PV source circuits
 +
|-
 +
|
 +
| = 4.4 A × 1 = 4.4 A
 
|}
 
|}
  
 
{| 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]]
 +
|-
 +
|
 +
| = 4.4 A ÷ 55 Ah = .08
 
|}
 
|}
  
−
If the number of PV modules does not meet the recommendations outlined above, increasing the PV source in size should be considered.
+
<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====
 +
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%;"
 +
! style="width: 20%"|Final number of PV modules
 +
! style="text-align:left;"| = 1
 +
|}
  
−
====Step 5: Final number of PV modules====
+
{| class="wikitable" border=1 style="width: 80%;"
−
A final number of modules should be chosen that can meet the requirements of Step 2, Step 3, and Step 4.
+
! style="width: 20%"|Final number of PV modules in series
 +
! style="text-align:left;"| = 1
 +
|}
  
−
====Step 6: Determine minimum current rating of charge controller====
+
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 20%"|Final number of PV source circuits
 +
! style="text-align:left;"| = 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.
 
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.
 
{| class="wikitable" border=1 style="width: 80%;"
 
{| class="wikitable" border=1 style="width: 80%;"
−
! style="width: 20%"|Minimum current rating of charge controller
+
! 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]]
 +
|-
 +
|
 +
| = 1 × 4.85 A × 1.25 = 6.1 A
 
|}
 
|}
  
 
====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]].
−
#Have a 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.
 +
 
 +
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 20%"|Number of charge controllers
 +
! style="text-align:left;"| = 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====
 
====Step 8: Determine final PV source power rating====
−
The total power rating of the PV source can be calculated by multiplying the power rating of the chosen PV module by the final number of PV modules (Step 5).
 
 
{| 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) × Number of PV modules (Step 5)
+
! style="text-align:left;"| = 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.
 +
 
 +
{| 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]]==
 +
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====
 +
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 33%"|Maximum circuit current
 +
! style="text-align:left;"| = [[PV module|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:
 +
<ol>
 +
<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#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>
 +
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 20%"|Total wire correction parameter
 +
! 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 (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)
 +
|-
 +
|
 +
| = 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 [[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>
 +
</ol>
 +
 
 +
====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:
 +
 
 +
<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
 +
|-
 +
|
 +
| = 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
 +
|}
 +
 +
{| 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%;"
 +
! 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
 +
|}
 +
 +
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 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
 +
|}
 +
 +
<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%;"
 +
! style="width: 20%"|Percentage voltage drop
 +
! 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
 +
|-
 +
|
 +
| = 15 A OCPD is equal to the maximum 15 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 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.
 +
 +
{| 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 × 1.25 A × 8m × 10.7 Ω ÷ 1000 = .21 V
 +
|}
 +
 +
{| class="wikitable" border=1 style="width: 80%;"
 +
! style="width: 20%"|Percentage voltage drop
 +
! style="text-align:left;"| = Voltage drop ÷ Circuit operating voltage x 100
 +
|-
 +
|
 +
| = .09 V ÷ 12 V × 100 = 1.75%
 +
|}
 +
 +
<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
Retrieved from "http://www.opensourcesolar.org/w/index.php?title=Detailed_DC_system_design&oldid=7886"