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Solar Panel Calculator

For help using this calculator please read through our detailed instructions.


  Calculation Type Value
Estimated Watt demand
3 Total Watts Per Hour (DC)
DC Amps x System Voltage
Hours per day
6 Hours Equip is expected to run (24hr)
as per application
Hrs d-1
Watt-Hours per day
9 Total daily usage
Watts x Hours
  Watt-Hrs d-1
Amp-hour calculation
10 Total watts
Daily requirements
  Watt-Hrs d-1
11 Corrected for battery losses
Assumes static average loss
  Watt-Hrs d-1
12 System voltage
DC voltage only
13 Amp-hours per day
Watts divided by Volts
  Amp-Hrs d-1
Battery bank calculation
14 # of days backup power required
Average 24 hour periods
15 Amp-hour storage
Raw capacity you need
16 Depth of discharge
Assumes 50%
0.5 fraction (enter decimal)
17 Required amp backup
Prevents excessive discharge
18 Battery Amp Rating (20 hr)
Battery Capacity in Amps
19 Actual # batteries wired in parallel
Raw number
20 Batteries wired in series
Relates to system voltage
21 Rounded number of Batteries
Always rounded up
Solar Panel Array calculation
22 Sun hours per day (Direct only)
Be realistic!
23 Worst-weather multiplier*
1.55 default
1.55 fraction
24 Total sun hours per day
Assumes average sun
25 Select panel size (Watt rating)
Watt hour rating
26 Nominal Panel Voltage
Approximate Solar output
16 Volts
27 Amps required from solar panels
Total daily consumption
15 Amps
28 Peak amperage of solar panel
Watts divided by Volts
29 Number of solar panels in parallel
Raw Number
30 Number of panels in series (12 V)
it is 1 for 12v, 2 for 24v, etc
31 Rounded number of solar panels
Always rounded up

Solar Calculator Notes and Instructions.

First, the notes: We hope this solar calculator will make sizing your panels and batteries a little less painful. Keep in mind that this is only a calculator, and it will directly reflect whatever you, the user, inputs into the fields. If your base calculations are off by even a little bit, the results reflected can be skewed by quite a bit, so view this as a guide, not an absolute. With that said, here comes the disclaimer. This calculator is for educational purposes only. is in no way responsible for the results of your calculations, and if you purchase a system based on the results of the Solar Calculator, BatteryStuff will not and cannot be held responsible for returns or exchanges for improperly sized systems. Normal RMA and exchange rules will apply to all solar panel purchases. See policies for more info.

Now the instructions:

Field #3: This field needs to be DC watt draw only. If you are using an DC to AC power inverter, meaning your device is rated in AC amps and 110 V, you will need to convert that number into DC watts before entering it in the field. Then you will need to add about 10% due to the inefficiency of the power inverter. To get there, use the following formulas;

1 Amp AC = 10 Amps DC. (example, 2AC amps =20DC amp)

Add 10% (22 amps)

DC amps x 12v = DC watts. (22 x12 =264 watts)

264 would be entered in field # 3

Fields #6 and #12 are for how many hours you expect your equipment to run in a 24 hour period, and your input voltage (12, 24, 36?).

Fields #14 and #18 will determine what size and how many batteries you need. In #14, insert days of backup you would like your battery pack to be good for. This is minus any solar panels, which we will figure in a minute. Field #18 is based on what battery you choose. Say you want to use a 55 AH battery because you like the dimensions, or maybe you like the 21 AH battery due to its terminal configuration. Enter your chosen battery amps there. We don’t like to see any battery discharged more than about 50%, so we will automatically adjust for that.

Still with me? Good, we are almost done. The last two fields, #22 and #25 are easy. How many hours of direct sunlight do you estimate your panel will get. Be realistic. We will then automatically guesstimate for clouds, bad weather etc. Field #25 is just like field #18 in the battery section. Look at our solar page, pick a panel you like and then enter the watts here.

Choose Your Solar Battery Charger

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