Solar plus battery: what happens during a power cut

A common surprise: a house with solar panels still loses power when the grid fails. That is by design, and a battery changes the picture.

Why panels alone switch off

A standard grid-tied solar inverter must stop feeding power when the grid goes down. Otherwise it would push electricity into wires a lineman believes are dead. So the panels may be in bright sun and your lights are still off.

What a hybrid system does

A hybrid unit contains an inverter that can form its own supply. When the grid drops, it disconnects from the grid in a fraction of a second and powers your chosen circuits from the battery, topping the battery up from the panels in daylight.

What to expect

• Only the backed-up circuits stay on. Heavy loads are best left off that board.
• On a sunny day, the panels can carry the daytime load and recharge the battery, so a long cut becomes manageable.
• At night, the battery alone carries the load, which is why we size it to the hours you need.

Panels first, or battery first?

If power cuts are your main problem, start with the battery. If the bill is, start with panels. A system with a solar input lets you do either first and the other later. More on solar and battery systems.