Off-Grid Solar Panel kW and Battery Storage Size Calculator
Off-grid sizing has two independent questions. The array must generate enough energy across an average day, which depends on peak sun hours at your latitude. The battery must carry the household through the night plus a run of poor weather, which depends on days of autonomy and how deeply the chemistry can safely discharge.
System losses of 20% cover inverter conversion, wiring, soiling, temperature derate and charge controller inefficiency.
| Peak sun hours | Array needed | Panels | Typical location |
|---|---|---|---|
| 3 h | 12.32 kW | 28 | Northern UK, Nordics |
| 3.5 h | 10.56 kW | 24 | Germany, Belgium |
| 4 h | 9.24 kW | 21 | Southern UK, NE US |
| 4.5 h | 8.21 kW | 19 | Central Europe, Midwest US |
| 5.5 h | 6.72 kW | 15 | Spain, Texas |
| 6.5 h | 5.69 kW | 13 | Arizona, Gulf, North Africa |
What peak sun hours actually mean
A peak sun hour is one hour of irradiance at 1,000 watts per square metre. A location with 4.5 peak sun hours receives that much total energy spread across a longer, weaker day. It varies by latitude, season and shading — winter values in northern Europe can be a third of the annual average, which is why off-grid systems are sized on the worst month, not the average.
Why eighty percent efficiency, not one hundred
Inverter conversion costs three to eight percent, wiring and connectors one to three, panel soiling two to five, high-temperature derate five to fifteen in hot climates, and charge controller losses two to five. Combined, a realistic system delivers seventy-five to eighty-five percent of nameplate output.
Depth of discharge decides real battery cost
A 10 kWh lead-acid bank at fifty percent DoD delivers 5 kWh usable; the same nominal capacity in LiFePO4 at ninety percent delivers 9 kWh and survives four to eight times more cycles. Compare batteries on cost per usable kilowatt-hour per cycle, not on nominal capacity.
Array size for common household consumption
| Monthly use | Daily use | Array at 4 sun hours | Array at 5.5 sun hours | Battery for 2 days (LiFePO4) |
|---|---|---|---|---|
| 300 kWh | 9.9 kWh | 3.1 kW | 2.2 kW | 22 kWh |
| 500 kWh | 16.4 kWh | 5.1 kW | 3.7 kW | 36 kWh |
| 750 kWh | 24.6 kWh | 7.7 kW | 5.6 kW | 55 kWh |
| 900 kWh | 29.6 kWh | 9.2 kW | 6.7 kW | 66 kWh |
| 1,200 kWh | 39.4 kWh | 12.3 kW | 9.0 kW | 88 kWh |
People also ask
How many solar panels do I need for 1,000 kWh per month?
About 10.3 kW at four peak sun hours with eighty percent system efficiency — roughly twenty-three panels rated at 450 W each.
How big should my battery bank be?
Multiply daily consumption by your desired days of autonomy, then divide by the usable depth of discharge. Two days at 30 kWh a day with LiFePO4 needs about 66 kWh nominal.
Should I size for winter or the annual average?
Off-grid systems must be sized on the worst month, otherwise you rely on a generator through winter. Grid-tied systems can use the annual average because the grid covers shortfalls.
Three worked examples
Same engine, three different starting points — useful if you want to see how sensitive the answer is before you type your own numbers in.
Example 1: monthly consumption 702 kWh, battery depth of discharge "LiFePO4"
On the lower / more conservative end. System losses of 20% cover inverter conversion, wiring, soiling, temperature derate and charge controller inefficiency.
Example 2: monthly consumption 900 kWh, battery depth of discharge "LiFePO4"
A typical middle-of-the-road setup. System losses of 20% cover inverter conversion, wiring, soiling, temperature derate and charge controller inefficiency.
Example 3: monthly consumption 1170 kWh, battery depth of discharge "Lithium NMC"
On the higher / more demanding end. System losses of 20% cover inverter conversion, wiring, soiling, temperature derate and charge controller inefficiency.
Quick answers about the Solar kW & Battery Storage
What exactly does the Solar kW & Battery Storage work out?
Off-grid sizing has two independent questions. You enter monthly consumption, peak sun hours, system efficiency and days of autonomy (plus 2 more optional details) and the result panel updates straight away, so you can compare two or three versions of the same question in a few seconds.
What do I need before I start?
Only 6 fields: monthly consumption, peak sun hours, system efficiency, days of autonomy, battery depth of discharge and panel rating. Nothing else is needed and nothing is stored.
What peak sun hours actually mean?
A peak sun hour is one hour of irradiance at 1,000 watts per square metre. The same maths runs inside this page, so hand-checking the result on paper gives you the identical figure.
Why do two calculators give me different answers for solar kW & Battery Storage?
Inverter conversion costs three to eight percent, wiring and connectors one to three, panel soiling two to five, high-temperature derate five to fifteen in hot climates, and charge controller losses two to five. Different sites pick different assumptions, so always check which method a calculator states before you trust the gap between two numbers.
What does the "Array size for common household consumption" table on this page tell me?
It is the reference range this tool works against — 5 rows from "300 kWh" (9.9 kWh) up to "1,200 kWh" (39.4 kWh). Use it to sanity-check whether the number you just calculated sits where you expected it to.
Which battery depth of discharge should I pick?
The dropdown offers 3 choices — LiFePO4, Lithium NMC and Lead acid AGM. Pick the one that matches your real situation rather than the one you would like to be true; battery depth of discharge usually moves the final figure more than any other single input, so it is worth running it twice with the option above and below your guess.
Does it work in both metric and imperial (or another currency)?
Yes. The "System efficiency" control converts every field and every result, so you never have to convert anything by hand before typing it in. Switch it after entering your numbers and the output re-renders instantly in the new system.
Do I have to press a button or reload the page to see the result?
No. Solar kW & Battery Storage runs completely inside your browser, so the moment you change a value the cards recalculate — there is no submit step, no page reload and no waiting for a server round trip. That also means it keeps working on a weak or intermittent mobile connection.
Is it free, and do you keep what I type?
It is free with no sign-up, no app install and no usage limit. Nothing you enter into Solar kW & Battery Storage leaves your device — the calculation is JavaScript running locally, so there is no upload of your figures to DrHint or anyone else.
Can I use it on a phone?
Yes — the layout stacks to a single column on small screens and the number fields open the numeric keypad on both Android and iOS. Many people bookmark this page or add it to their home screen and re-open it whenever the question comes up.
Anything to be careful about with the result?
About 10. Treat the output as a well-grounded estimate for planning, not as a professional, legal or medical decision on its own.
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