Find the optimal battery size and calculate your additional savings
Use this free calculator work out if a solar battery makes sense for your setup. It’s modelled using a 5% average annual energy inflation rate, which is pretty conservative.
Start by entering your existing or planned solar system size. Then input your daily electricity usage — you can find this on your energy bills or smart meter app (divide your annual usage by 365). Select the usage pattern that best matches your lifestyle, as this significantly affects how much solar you already use directly. Finally, add your electricity rate and any off-peak tariff if you have one. The calculator will recommend an optimal battery size and show whether it’s a worthwhile investment for your situation.
This is the sweet spot for your setup — large enough to capture most of your excess solar generation, but not so large that you’re paying for capacity you’ll never use. The calculator considers your surplus generation, evening usage patterns, and practical battery sizes available on the market. For detailed information on battery pricing and specifications, visit our solar battery costs guide.
This shows what percentage of your solar generation you use yourself rather than exporting to the grid. Without a battery, most UK homes achieve 30-50% self-consumption. A well-sized battery can increase this to 70-85%, meaning more of your free solar electricity powers your home instead of being sold back at lower export rates.
This is the additional money you save each year by adding a battery to your solar system. It accounts for the electricity you no longer buy from the grid, minus the export income you lose by storing instead of selling. The net benefit depends heavily on the gap between your import rate (what you pay) and export rate (what you earn).
How long until your battery savings equal the installation cost. A payback under 10 years is generally considered worthwhile since quality batteries last 10-15 years. Payback over 15 years suggests a battery may not be the best investment right now. For detailed pricing information, see our solar battery costs guide.
If you have a time-of-use tariff like Octopus Go or Economy 7, your battery can charge overnight at cheap rates (often 7-12p/kWh) and power your home during expensive peak hours (24-35p/kWh). This arbitrage is especially valuable in winter when solar generation is low but the price difference remains.
For a typical 4kW system, most households benefit from a 5-6.5kWh battery. This captures the bulk of excess generation on good days without overspending on unused capacity. If you’re out all day and have high evening usage, you might benefit from a larger 8-10kWh battery.
Most lithium solar batteries are warranted for 10 years and typically last 10-15 years in practice. They gradually lose capacity over time — expect around 70-80% of original capacity after 10 years. The number of charge cycles also affects lifespan, but most home batteries won’t hit cycle limits before age-related degradation.
Yes, batteries can be retrofitted to most existing solar installations. AC-coupled batteries work with any inverter, while DC-coupled options may need a compatible hybrid inverter. Retrofitting typically costs slightly more than installing with a new solar system due to additional wiring and potentially a new inverter.
Not automatically. Most standard battery installations switch off during grid outages for safety reasons. If backup power is important to you, you’ll need an EPS (Emergency Power Supply) setup, which costs extra and may only power essential circuits. Some batteries like the Tesla Powerwall include backup capability as standard.
Popular choices include GivEnergy (great value, good app), Tesla Powerwall (premium, excellent backup), and SolarEdge (integrates well with their inverters). The “best” battery depends on your budget, required capacity, and whether you want features like backup power or smart tariff integration. For a comprehensive comparison, see our best solar batteries guide. Always compare quotes from MCS-certified installers.
A solar battery can be an excellent investment if your situation is right — particularly if you’re out during the day, have high electricity rates, or access to cheap overnight tariffs. Use this calculator to understand whether the extra savings justify the upfront cost for your specific setup. For help choosing the right battery for your needs, check out our best solar batteries guide. Remember that battery prices continue to fall while electricity prices remain high, making the economics increasingly attractive for UK homeowners.