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Solar Battery Size Calculator

Find a useful battery size for your PV system. The calculator compares smaller, suitable and larger batteries and shows where extra capacity adds little value.

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The battery size result gives not only a battery size, but also whether a larger battery still adds meaningful economic value.

Display currencyChoose the currency symbol for entered amounts and results. No exchange-rate conversion is applied.
You can find this on your electricity bill. It limits how much solar power can realistically be used on site.
If unknown: PV size in kWp × roughly 900–1,000 kWh/kWp/year as a first estimate.
The higher the electricity price, the more valuable each shifted solar kWh becomes.
Battery value is roughly electricity price minus feed-in tariff.
Rough assumption for charge/discharge losses. A lower efficiency reduces the usable shifted kWh.
Use the installed battery price divided by usable battery capacity.
Economics favors smaller batteries with better payback. Maximum autonomy allows larger batteries even when added value rises more slowly.
FAQ

FAQ about Solar Battery Size Calculator

What battery size is useful?

A useful size is often close to the demand that can realistically be shifted into evening or night hours. The calculator makes clear when extra capacity adds little value.

Why can a smaller battery be more economic?

Smaller batteries are used more often. Larger batteries may increase autonomy but can perform worse economically.

Is the scenario reference size a purchase recommendation?

No. It is a comparison point from annual totals and a capped load-profile heuristic, not an hourly profile, weather year or binding design. Check quotes, measured demand, warranty, entered round-trip efficiency and installation separately.

Why does the size comparison matter most?

Because the main question is not only whether a battery pays off. The comparison shows where extra capacity starts to add much less value.

Does the calculator include winter and weather?

Only in a simplified annual model. Monthly data and load profiles are more accurate for real design.