Solar Battery Sizing Calculator

Estimate the solar battery size that may fit your home based on off-sunlight consumption, coverage target, optional backup needs and an indicative installed cost range.

Indicative result

A practical first estimate for a home solar battery

This calculator helps you estimate how much solar battery storage may suit a grid-connected home. The focus is on how much of your electricity use happens outside sunlight hours, what share you want the battery to cover and whether you also want a basic backup reserve for essential loads.

kWh vs kW

Battery size is expressed in kWh. Appliance power is expressed in kW or W. They are different concepts and should not be mixed.

Electricity consumption

We start from your annual or monthly electricity use, convert it into daily consumption and estimate which part happens outside solar production hours. Then we apply the battery coverage target you choose.

Advanced settings
Indicative result

Enter your figures to get a clear battery estimate

You will see a nominal battery recommendation, approximate usable capacity, nearby commercial sizes and an indicative cost range for a residential self-consumption setup.

How this calculator works

We start from your annual or monthly electricity use, convert it into daily consumption and estimate which part happens outside solar production hours. Then we apply the battery coverage target you choose.

If you enable the backup block, the tool compares that daily need with the energy required to keep essential loads running during an outage. The final result uses the larger of both needs and converts it into nominal battery capacity using depth of discharge, efficiency and a safety margin.

What affects solar battery size

A battery should not be sized just from the number of panels or the floor area of the house. The key factor is how much energy you want to shift into the evening, how much of your residential demand happens outside sunlight hours and how much autonomy you expect.

  • Your real or reasonably estimated daily electricity use.
  • The share of consumption that happens when solar production is no longer available.
  • The percentage of that off-sunlight demand you want the battery to cover.
  • The battery chemistry and therefore its usable energy fraction.
  • Whether you also want basic outage backup for a fridge, lights, router or other essential loads.

Nominal capacity vs usable capacity

Nominal capacity is the total battery size, expressed in kWh. Usable capacity is the energy you can realistically draw from it while accounting for operating limits and system losses.

That is why two 10 kWh nominal batteries do not always deliver the same usable energy. In this calculator we apply depth of discharge and system efficiency to estimate how much usable storage remains available under normal conditions.

How to read the result

The recommended option points to a commercial size close to the calculated value. The tighter option is useful if you want to prioritise budget knowing that less nighttime demand will be covered, while the larger option leaves more room for peaks, variable habits or future electrification.

If the result goes above 30 kWh, it usually makes sense to review the design with an installer because that already points to a large residential system. Even so, the exact calculated figure is still useful as an initial reference.

Frequently asked questions about home solar batteries

These answers address the most common doubts when a household wants to know whether a 5, 10, 15, 20 kWh battery or a larger unit makes sense.

What size solar battery do I need for my house?

It mainly depends on how much electricity you use outside sunlight hours and what share of that demand you want the battery to cover. In a grid-connected home, house size or panel count alone is usually not enough.

How much battery do I need to use solar energy at night?

You need enough usable capacity to cover the nighttime share you want to shift. The calculator first estimates off-sunlight consumption and then converts it into nominal battery capacity.

What matters more: the solar panels or nighttime consumption?

For battery sizing, nighttime consumption and your coverage target usually matter more. Panels are important to recharge the battery, but usable storage size is mainly driven by the energy you want available when the sun is gone.

What is the difference between kWh and kW?

kWh measures energy stored or consumed over time, while kW measures instantaneous power. A battery is sized in kWh, while an appliance or group of loads is described in W or kW.

What does usable battery capacity mean?

It is the energy you can actually use from the battery in normal operation. It is usually lower than nominal capacity because allowable depth of discharge and system losses reduce what is available.

Would a 5 kWh battery work for me?

It may suit homes with moderate nighttime demand and a partial coverage target, but it is not always enough. This calculator helps you see whether 5 kWh fits your case or whether 7.5, 10 or 15 kWh would be more realistic.

Does the result include outage backup?

Only if you enable the backup block. If you keep it off, the recommendation is based only on off-sunlight consumption and not on outage autonomy.

Is a bigger battery always better?

Not necessarily. An oversized battery can cost much more and may take longer to justify if your real nighttime demand does not support that size.

Does this calculation work for any country?

Yes as a general energy estimate, because the model is based on consumption, coverage and efficiency. However, final costs, rules and hardware choices can vary by country and by the actual installation.

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