The answer
Is a bigger battery always better value?
The right battery is the one you can use, not the largest you can buy. Size it around the solar surplus you actually have, the electricity you use after sunset and any deliberate off-peak charging plan.
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Find the electricity available to store
First estimate solar generation by time of day, then subtract electricity the property will use immediately. The remainder is potential surplus for a battery. A summer afternoon may leave plenty; a dark winter day may leave almost none. An annual solar total cannot tell you how often the battery would fill.
Smart-meter half-hourly data helps show evening and overnight demand. If the home may add a heat pump or EV, model that as a separate future scenario rather than pretending the load already exists. The right size depends on usable capacity, not only the number printed on the battery casing: some stored energy is held back to protect the battery.
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Compare a small, medium and large option
Ask how often each proposed capacity would charge and discharge through a typical summer, shoulder-season and winter week. A larger battery may catch more surplus on a sunny day but sit partly empty in winter, while a small one may fill early and export the rest. Show the extra useful electricity moved by each size, not only a rising 'self-consumption percentage'.
Charging and discharging lose energy. Compare the value of electricity released later with both the export payment you forgo by storing solar and the installed battery cost. If you plan to charge from a time-of-use tariff, include the cheap-period unit price, losses and the expensive hours avoided. A battery that looks attractive under today's tariff might be less so if tariff terms change.
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Is backup power part of the decision?
Do not assume a grid-connected battery will keep sockets on during a power cut. Backup requires compatible inverter hardware, safe isolation and a decision about which circuits to supply. A few lights and a router have a different power demand from a cooker or heat pump. Ask the installer to specify the supported loads and expected duration at the usable stored energy.
Check the warranty's time, cycle and retained-capacity terms, where the unit can be installed, and what happens when it eventually needs replacement. Energy Saving Trust notes that battery life is shorter than panel life. Storage can be worthwhile, but solar-only, solar-plus-battery and tariff-charging options should be shown side by side for your actual use pattern.
Where this guidance comes from
Check the original guidance.
These primary sources support the technical or scheme points above. Rules can change; follow the current source before making a commitment.
Apply this to your property
Would storage earn its place at your property?
FLO can review your generation, usage times and tariff before recommending a battery size—or deciding that solar alone is the better first step.