Battery Storage Calculator
What size solar battery do you need? Enter your solar array size (in kWp) and roof orientation below — our calculator recommends the ideal battery storage capacity for your setup.
How our battery storage calculator works
The calculator estimates your daily solar generation using standard UK yield figures for your roof orientation. We then assume approximately 35% of generation is used immediately (self-consumption) — this is electricity you consume while the panels are producing. The remaining 65% is surplus that could be stored in a battery for use in the evening or overnight.
We add a 15% headroom for depth-of-discharge (DoD). Lithium batteries shouldn't be fully drained, so the actual battery capacity needs to be slightly larger than the usable energy stored each day. The recommended size is then matched to the nearest standard modular battery capacity.
Factors that affect battery sizing
Your daily and seasonal energy consumption pattern is the most important factor. Here's what to consider:
- When you use electricity — if you use most of your power during the day, you'll have more surplus to store. Heavy evening users benefit from a larger battery.
- Time-of-use tariffs — charge your battery on cheap overnight electricity (e.g. Octopus Agile or Go) and use it during peak hours for significant savings.
- Backup power requirements — if you need the battery to keep critical systems running during power cuts, you may want a larger capacity or an emergency power output.
- System expansion plans — modular batteries can be expanded later, so you can start small and add capacity as your needs grow.
- Seasonal variation — solar generation is much higher in summer than winter. Your battery should be sized for a realistic year-round balance, not just peak summer.
Understanding depth of discharge and self-consumption
Depth of discharge (DoD) refers to how much of the battery's capacity is actually used. Most modern lithium batteries are designed for 80–90% DoD — draining them fully reduces their lifespan. Our calculator builds in headroom so you don't regularly discharge your battery beyond safe limits.
Self-consumption is the proportion of your solar generation that you use directly rather than exporting to the grid. The higher your self-consumption, the more value you get from your solar panels. A battery helps by storing surplus daytime generation for use when the sun isn't shining, typically increasing self-consumption from around 30–40% to 60–70% or more.
Standard modular battery sizes are 5, 7.5, 10, 15, 20 and 25 kWh. Systems can be scaled by adding additional modules, and most modern batteries are compatible with all major solar PV systems and inverters.
Maximise your solar self-consumption
We install battery storage systems across the East Midlands — for homes, commercial premises, farms, churches and heritage buildings. Whether you have an existing solar array or are planning a new installation, we'll help you choose the right battery system to maximise your energy independence and reduce your reliance on the grid.