How Battery Storage Works

A home battery stores surplus electricity from your solar panels and releases it when panels are not generating — typically in the evening and overnight. Without a battery, that surplus goes to the grid at low export rates instead of reducing your import bill.

What is inside a home battery

Almost all domestic batteries sold in the UK today use lithium-ion chemistry — the same technology as your phone or EV, scaled up to 5–15 kWh of capacity. Inside is a battery management system (BMS) that controls charge and discharge rates, monitors cell temperatures, and prevents overcharging or deep discharge that would shorten the battery's life.

AC-coupled vs DC-coupled

AC-coupled batteries — the most common type — connect to your home's AC circuit alongside your existing solar inverter. They are easier to retrofit to an existing system but involve two conversion steps, which creates a small efficiency loss of around 10%.

DC-coupled batteries connect before the inverter, storing electricity in DC form before it is converted. They are more efficient but typically require a hybrid inverter installed at the same time, making them better suited to new installations.

How the system decides what to charge and discharge

A charge controller or hybrid inverter monitors solar generation, household consumption, and battery state in real time. It prioritises powering your home from solar first, then charges the battery with surplus, then exports what remains. At night, it draws from the battery before switching to grid import.

Smart tariff charging

Modern batteries can also be charged from the grid at cheap off-peak rates — particularly useful on tariffs like Octopus Go where night-time units can be 7–15p/kWh. The battery is then discharged during the morning peak when grid electricity costs 28p+ per unit.