Capacity check · 15 kWh
15 kWh home battery: does this capacity fit?
A 15 kWh home battery provides more storage than a smaller system. That extra room is useful only if you can regularly charge it and use the stored power later. Having a heat pump or car alone does not justify choosing 15 kWh.
Free and no obligation · Sizing advice based on your situation
- Use your own consumption
- A guideline gives a starting point, not a final size.
- Generation alongside usage
- Check how much surplus you can actually store.
- Larger is not always better
- Choose based on usage, not storage space alone.
When should you consider 15 kWh?
Is your heat pump or car already included in annual consumption? Do not add a fixed allowance on top. New equipment needs a separate estimate.
- Use measured total annual consumption, including existing appliances.
- Do not count an existing heat pump or car again as an allowance.
- Estimate planned equipment separately.
- Check whether extra demand occurs when the battery can deliver.
Example with 7,500 kWh annual consumption
This is a worked example, not an average household. The consumption guideline uses 60 to 80% of average daily usage. Solar panels and your usage pattern still need a separate assessment.
- Annual consumption (assumed)
- 7,500 kWh
- Daily average: annual consumption / 365
- 20.5 kWh
- Lower guide: daily average × 0.6
- 12.3 kWh
- Upper guide: daily average × 0.8
- 16.4 kWh
- Solar panel output
- Not specified, assessment needed
15 kWh falls within this range, but that does not make it a product recommendation. Actual use depends on generation, direct consumption, losses and the installation.
Is 15 kWh too small, right or too large?
Too small if…
When measured later-day demand needs more and sufficient solar surplus is available. Having two large appliances alone does not justify 20 kWh.
Right if…
When the extra storage is used regularly. At the assumed annual consumption of 7,500 kWh, the guideline gives 12.3 to 16.4 kWh, which includes 15 kWh.
Too large if…
When advice already fully includes future equipment you do not use yet. Assess current needs first, then a possible expansion scenario.
Capacity, power and installation
15 kWh describes an amount of energy. kW describes power: how quickly the system can deliver it. The number of phases does not follow from kWh alone. Compare nominal and usable capacity; the product label is not necessarily the energy delivered to your home. Assess the inverter, consumer unit, location and any backup function separately.
Nominal and usable capacity
Compare kWh on the same basis. Ask which capacity is available for use and which reserve and conversion losses apply.
Power in kW
Capacity in kWh says how much energy can be stored. Charging and discharging power in kW also determines which appliances the system can support at the same time.
Expansion and backup
Check whether modules can be added later and whether backup is supported. Both depend on the model, inverter and installation.
Expanding later: check before choosing
A planned heat pump changes more than the annual total: consumption across the year also changes. Agree an expansion scenario with the installation partner and ask about conditions for the selected system.
Compare capacities
Frequently asked questions about 15 kWh
Does a heat pump automatically mean 15 kWh?
No. For an existing heat pump, use measured total annual consumption. For a planned heat pump, that measurement is not available yet. Heat demand and solar generation also do not always coincide. This needs a separate assessment, not a fixed allowance.
Which guideline does the calculation use?
The consumption guideline of 60 to 80% of average daily usage gives an initial range. For solar panels, 1 to 1.5 kWh per kWp is a separate guide. If the ranges do not overlap, ask for an assessment.
Is nominal capacity the same as usable capacity?
No. Nominal capacity is the stated total storage; usable capacity accounts for the portion the system makes available. Charging and discharging also cause losses. Ask for comparable specifications before choosing a model.
Curious which capacity fits your home?
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