What is home battery storage?
A home battery storage system is an electrochemical device that stores electrical energy and releases it on demand. Most modern home batteries use lithium iron phosphate (LFP) chemistry — a type of lithium-ion cell chosen for its safety profile, longevity and thermal stability.
The battery connects to your home's electrical supply via a hybrid inverter, which manages the flow of energy between solar panels (if fitted), the battery, your home and the grid. When solar panels generate more electricity than your home needs, the inverter charges the battery. When your home needs more electricity than the solar panels are producing, the inverter draws from the battery. If both are depleted, it falls back to the grid.
Without solar panels, a battery can still be charged directly from the grid — typically overnight on a cheap-rate tariff — and discharged during peak hours when grid electricity is most expensive. This is called energy arbitrage.
How to size a home battery correctly
Battery capacity is measured in kilowatt-hours (kWh). A typical UK home uses 8–12 kWh of electricity per day, though this varies significantly by household size and appliances. The goal is not to store everything — it is to store enough to cover your evening and overnight usage, or to span a specific window you are trying to avoid (such as peak grid pricing hours).
For households on a time-of-use tariff like Octopus Agile or Intelligent, the target is typically to store enough cheap overnight energy to cover the next day's peak hours (usually 4–7pm). For households with solar panels, the target is to store excess daytime generation for use in the evening.
As a rule of thumb: a 5 kWh battery suits a 1–2 person home with low consumption; a 10 kWh battery suits a 2–4 person home with average consumption; a 15–20 kWh system suits larger households or homes with high consumption, EVs or heat pumps. These are starting points — a site survey will produce a specific recommendation based on your actual usage data.
One important factor: battery capacity on paper is not the same as usable capacity. Most manufacturers recommend cycling between 10% and 90% to preserve battery life. A 10 kWh battery typically delivers 8–9 kWh of usable capacity in practice.
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