Calculators / Batteries and solar
What off-grid solar system do you need?
Put in what you use a day and how much sun you get. You’ll get the panels, the battery bank and the charge controller, sized with the makers’ own rules.
Updated · How we check our numbers
Your off-grid system
4 × 430 W, 469 Ah
1,720 W of panels, a 469 Ah battery bank at 24 V (11.3 kWh), and a 60 A MPPT controller, for 3,000 Wh a day.
- Panels
- 1,720 W4 × 430 W
- Battery
- 469 Ah11.3 kWh at 24 V
- Controller
- 60 A
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Estimate for planning only, not professional advice. Check the manufacturer’s instructions, your local code and a licensed professional before you buy, build or install. Use at your own risk. Terms.
array = 3,000 Wh × 1.2 × 1.2 ÷ 3 h = 1,440 W
bank = 3,000 Wh × 3 ÷ 0.8 ÷ 24 V = 469 Ah
controller = 1,720 W ÷ 28.8 V = 59.7 A
cold Voc = 38.91 V × (1 + -0.24% × (-17.8 − 25 °C)) = 42.9 V
What to buy
24 V system- 4 panels1,440 W needed: 3,000 Wh × 1.2 × 1.2 ÷ 3 sun hours1,720 W
- Battery bank3,000 Wh × 3 days ÷ 80% usable = 11,250 Wh469 Ah at 24 V
- Charge controller (MPPT)1,720 W ÷ 28.8 V charging60 A
- Panels in series on a 100 V controller42.9 V per panel at 0°F (Voc 38.91 V)up to 2
- Panels in series on a 150 V controller42.9 V per panel at 0°F (Voc 38.91 V)up to 3
- Panels in series on a 250 V controller42.9 V per panel at 0°F (Voc 38.91 V)up to 5
Morningstar, Renogy and Victron sizing rules. A design check, not an engineered system.
Peak sun hours are the hours of full sun the day’s light adds up to. Morningstar sizes an off-grid array for the month with the least sun, so use your winter figure, not the yearly average, if you need power year round.
We count 80% of a lithium bank as usable (Renogy: “Do not exceed 80%”). Battle Born rates its batteries for 100%, which would shrink the bank by a fifth.
Choose the next size up from 60 A. Victron allows up to 130% oversizing on its MPPT controllers, but don’t exceed the controller’s maximum PV voltage, below.
How we work it out
panels (W) = daily Wh × 1.2 × 1.2 ÷ peak sun hours
Morningstar sizes an off-grid array to make at least 115 to 120% of the daily load in the month with the least sun, then about 20% more on top of that. Use your winter sun hours if you need power all year.
battery (Ah) = daily Wh × days of autonomy ÷ usable share ÷ system volts
Morningstar suggests 4 to 5 days of autonomy in many places, 2 to 3 with a generator. Only part of a bank is usable: half of a lead-acid battery (Morningstar), and we count 80% of lithium (Renogy; Battle Born rates 100%).
controller (A) = panel watts ÷ charging volts · cold Voc = Voc × (1 + β × (T − 25 °C))
Renogy's formula, at 14.4, 28.8 or 57.6 V charging. Panels make more voltage in the cold, so the number you can wire in series is set by your coldest morning and the controller's maximum PV voltage, as Victron warns. The default panel is a Silfab SIL-430 QD.
Solar output by ZIP comes from PVWatts v8, from the National Laboratory of the Rockies (formerly NREL). The laboratory provides the data as is, without warranty, and doesn't endorse this calculator.
Where the numbers come from
- PVWatts v8 API, National Laboratory of the Rockies (developer.nlr.gov)
- Morningstar: basic system sizing design concepts
- Morningstar: off-grid PV sizing and partial state of charge
- Morningstar: design factors for lead-acid batteries
- Renogy: solar charge controller sizing
- Victron Energy: matching solar modules to MPPT charge controllers
- Silfab: SIL-430 QD datasheet
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