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Tools  /  Solar & Battery Calculator   Free

Size a solar system that actually keeps the lights on.

Most "solar calculators" size a grid-tie system to shave your bill. This one sizes for independence: list your real loads, size the array for your latitude and the season you need it, and size a battery bank to carry you through the nights and cloudy stretches — for as many days of autonomy as you want.

1

What you need to run

List the loads you want to power. Edit the watts and hours-per-day to match your gear — the presets are typical. Hours already account for cycling on fridges and freezers.
2

Your solar array

How big an array it takes to make that energy where you are. Off-grid systems should size for winter — the sun is weakest exactly when you need heat and light most.
What the array generates per day
3

Your battery bank

Enough storage to run through the night and carry you across cloudy days. "Days of autonomy" is how long the bank alone can power your loads with no sun.
4

Recharge time & system summary

How long a run of sunny days takes to refill a drained bank with this array — and the whole system at a glance.
Days of sun to refill a fully drained bank — loads still running
…with loads switched off

Power is the multiplier. Size it honestly.

Pair it with a heat plan and the rest of your system.

Size backup heatingAdd it to your plan