Electrical Characteristics
A1
Inverter efficiency
80
90
A2
Battery bus voltage
12
24
A3
Inverter AC voltage
230
380
%
48
V
V
Load Estimation
A4
A5
A6
A7
A8
Adjustment
Factor 1 for
DC A1 for AC
Adjusted
wattage
(A4/A5)
Runtime
(Hrs)
Energy Per
Day (Wh)
(A6 x A7)
No.
Appliances
Rated
Wattage
(Watts)
1
LED bulbs
11
6
66
0.8
83
5
413
2
Mobile phones
20
3
60
0.8
75
2
150
3
Air conditioners
120
2
240
0.8
300
4
1200
4
Refrigerator
100
1
100
0.8
125
12
1500
Qty
Total
Watts
466
583
3263
A9
Total Energy Demand Per Day (Sum of A8)
3263
Watt-Hours
A10
Total Amp-Hour Demand Per Day (A9/A2)
272
Amp-Hours
A11
Maximum AC Power Requirement (Sum of A4)
466
Watts
A12
Maximum DC Power Requirement (Sum of A6)
583
Watts
Battery Sizing
B1
Days of Autonomy
3
Days
B2
Allowable Depth of Discharge Limit
0.8
Per Unit
B3
Required Battery Capacity [(A10 x B1)/B2]
1020
Amp-Hours
B4
Selected battery capacity
200
Amp-Hours
Selected battery voltage
12
Volts
Number of batteries in parallel(B3/B4)
5.10
B5
6
Batteries
B6
Number of batteries in series (A2/Selected battery voltage)
1
String
B7
Total number of batteries needed (B5 x B6)
6
Batteries
B8
Total rated amp hour capacity needed (B4 x B7)
1200
Amp-Hours
3262.50
Watt-hours
0.85
Per Unit
PV Array Sizing
C1
Total Energy Demand Per Day (A9)
C2
Battery Round Trip Efficiency
C3
Required Array Output Per Day (C1/C2)
3838.24
Watt-hours
C4
Selected PV module max Power voltage @ STC
14.705
Volts
(voltage @ Pmax x 0.85)
C5
Selected PV module guaranteed output
80
Watts
C6
Peak Sun Hours
6.5
Hours
C7
Energy Output per module per day (C5 X C6)
520
Watt-hours
C8
Module energy output @ operating temperature (DF x C7)
468
Watt-hours
DF = 0.8 for hot climates & DF = 0.9 for moderate climates
C9
Number of modules required to meet energy requirement
8.20
(C3/C8)
9
C10
Number of modules required per string rounded to the next
Modules
0.82
higher integer (A2/C4)
C11
Number of strings in parallel rounded to the next
1
Strings in series
9
Strings in parallel
higher integer (C9/C10)
C12
Number of modules to be purchased (C10 x C11)
9
Modules
C13
Nominal rated PV module output
80
Watts
C14
Nominal rated array output (C12 x C13)
720
Watts
Inverter Sizing
1
The input rating of the inverter should never be lower than the total power (watts)
2
The inverter must have the same nominal voltage as your battery (the inverter is rated in Watts)
3
The size of an inverter for standalone system is measured by its maximum continuous output
in watts and this rating must be larger than the total wattage of all the connected AC loads.
4
This high starting power consumption can be more than twice the normal power consumption
so the input rating of the inverter should be ideally 25-30% bigger than the rated wattage
of your appliances
Total connected AC load(Sum of A4)
466
Add 25% of starting power consumption (Sum of A4 x 1.25)
583
So 12 V, 600 Watts inverter will be suitable
Charge Controller Sizing
1
The function of a charge controller is to regulate the charge going into battery bank from solar
panel array and prevent overcharging and reverse current flow at the night
2
Most used charge controllers are Pulse Width Modulation (PWM) or Maximum Power Point
Tracking (MPPT).
3
The voltage at which PV module can produce maximum power is called maximum power point
(or peak power voltage)
4
Maximum power varies with solar radiation, ambient temperature and solar cell temperature.
5
Typical PV module produces power with maximum power voltage of around 17 V when
measured at cell temperature of 25 0C it can drop to around 15 V on a very hot day and it can
also rise to 18 V on a very cold day
6
When a MPPT solar charge controller notices variations in current-voltage characteristics
of solar cell, it will automatically and efficiently correct the voltage. It forces the PV module to
operate at a voltage close to maximum power point to draw maximum power available
7
MPPT solar charge controller allows users to use PV module with a higher voltage output than
operating voltage of battery system
8
For example, if PV module has to be placed far away from charge controller and battery, its wire
size must be very large to reduce voltage drop. With a MPPT solar charge controller, users can
wire PV module for 24 V or 48 V (depending on charge controller and PV modules) and bring
power into 12 V or 24 V battery system
9
This means it reduces the wire size needed while retaining full output of PV module. The charge
controller current input rating is equal to the product of the short circuit current, the PV module, number of
PV
module in parallel and safety factor where the safety factor is 1.25
Therefore, I Rated = (NPVparallel x I sc) x 1.25
IRated = Solar charge controller rating
ISC = Short circuit current
NPVparallel = Number of PV modules in parallel
Safety factor = 1.25
For the the example the charge controller size will be (9 x 6.15 x 1.25)
69.19
70
So a 12 V, 70 A Charge Controller will be required
Design Summary
1
9 Solar modules of peak voltage 17.3 V, short circuit current 6.15 A and peak current 4.63 A are
to be connected in parallel. The minimum PV array ouput per day to be 3838.24 Watt-hours
2
Battery capacity should be a minimum of 1020 Ah. Battery can be discharged up to 80% and
charging losses are 20%.. The battery has a reserve capacity of 3 days
3
A 12 V, 600 Watts Inverter of efficiency 80 % to be used
4
A 12 V, 70 A charge controller to be used
5
The PV system is designed for a 12 V operation
6
Cable sizing has been determined by using rule of thumb but the actuals can be found by
using the formulars once critical equipment distances have been determined
720 Wp
PV Array
4 mm2
2
12V , 70A
Charge
Controller
4 mm2
4 mm2
2
12 V , 1200
. Ah
Battery Bank
2. 5 mm2
2
2
0 KWh/Day
DC Loads
2. 5 mm2
2
12 V , 600 W
Inverter
1. 5 mm2 3838.2
.
KWh/ Day
AC Loads
2. 5 mm2
2
2