What decides the battery size?

The goal decides it. Backup, peak shaving and self consumption each call for a different capacity and power.

Does a battery work without solar?

Yes. A battery can charge from the grid, though pairing it with solar usually changes the running cost more.

Why does the panel matter?

The battery and its inverter need space and capacity in the electrical panel, so the electrical trade is part of the design.

How batteries work with solar on a project

What a battery does on a home or a small commercial job, and how it changes the numbers.

Steps in this animation

1. Midday. Solar production runs the house and charges the battery. Anything left over can go to the grid.
2. Evening. The sun sets and the panels stop producing. The battery serves the house instead of the grid.
3. Outage. The grid goes down and the battery keeps the circuits you chose running.
4. The grid returns. The grid comes back and the battery recharges, ready for the next day.

A battery changes when a building uses the energy it makes. That change shows up in the running cost, in the backup the customer gets and in the payback of the whole job.

How it works

Solar production charges the battery first, then serves the building. Anything left over can go to the grid. In the evening the battery serves the building instead of the grid, which is when the value is highest on many rate plans.

The inverter decides where the power goes, so the battery and the array are designed together. On a job with backup in mind, the battery also carries the circuits the customer chooses to keep running during an outage.

Key terms

Capacity is how much energy the battery can store.
Power is how much it can deliver at one moment.
Peak shaving is using stored energy to avoid the most expensive hours.
Backup circuits are the loads a battery keeps running during an outage.

Where it fits in a project

Storage is usually sized with solar and the electrical panel, since the battery adds load and needs a place in the panel. The size of the battery then changes the cost and the payback that appear in the proposal next to every other trade.

Filed under Storage explainers in the Learn hub.