Battery backup: essential circuits or the whole home?

First, check that outage operation is part of the design

Many grid-connected systems stop supplying the property when the grid fails. Outage supply requires compatible equipment and a configuration that can safely operate independently of the grid. Having panels and a battery is not enough to establish that capability.

Have the proposal specify the backup arrangement and any additional equipment or switchboard works. Ask what happens when the grid fails, which loads remain supplied and whether there is an interruption during the transition.

Write an appliance list, then confirm the circuits

Begin with a priority list: refrigeration, selected lighting, communications and any other loads important to your household. Add the model or rated demand where it is safely available. Your electrician needs to translate that list into a practical circuit arrangement.

A kitchen circuit may supply more than the appliance you had in mind. Discuss which sockets and appliances will be supported, labelled or excluded. Do not assume that “essential circuits” means every socket in an essential room.

For a whole-home proposal, ask what happens if several high-demand appliances run together. Whole-home connection is not a promise that every appliance can operate simultaneously. Three-phase supply and appliance starting demand need explicit consideration.

• Which fridge, lighting circuits and communications devices are priorities?
• Are heating, electric cooking, hot water or EV charging excluded?
• What simultaneous load and starting-demand limits apply?
• How will supported circuits be identified at handover?

Treat runtime figures as conditional examples

Capacity in kWh describes stored energy; output in kW describes the rate of delivery. A battery can have charge remaining but still be unable to support an appliance combination that exceeds its output.

Ask for estimates at several load levels and starting charges. A battery partly discharged before an outage has a different starting point from one at its chosen reserve. The reserve setting should be discussed alongside everyday operation.

Can your panels recharge the battery while the grid is down?

This is a separate compatibility question. Some configurations can recharge from solar during an outage; others cannot. Request the behaviour of your proposed equipment combination in writing, including what happens when available battery charge becomes low.

At handover, ask for a commissioning record of the agreed backup functions and instructions for monitoring, load management and grid restoration. Never bypass isolation equipment or improvise electrical connections.

If anyone relies on electrically powered medical equipment, develop a separate contingency plan with the equipment provider and relevant health professionals. General household battery guidance is not a guaranteed life-support arrangement.