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Solar Installer GuildUnited States · independent

Before you decide

Do I need a battery with solar?

The short answer

It depends which of two problems you are solving. If you want power during an outage, you need a battery and specific switching, because a grid-tied system without one shuts down when the grid does. If you are solving for economics, it depends entirely on how your utility credits exports — where that credit is low, a battery earns its keep by shifting your own consumption.

Backup and self-consumption are different purchases

  • Backup requires additional switchgear to isolate your house from the grid, and it usually covers selected circuits rather than the whole property. Decide which circuits before the design is drawn.
  • Self-consumption stores midday surplus for evening use, and its value is the difference between what you would have been credited for exporting and what you would have paid to buy it back.
  • A grid-tied system with no battery produces nothing during an outage, by design, for the safety of anyone working on the network. This surprises people and it is not a fault.

What to ask about any battery quote

  1. Usable capacity, not nameplate capacity, and the continuous and peak power output.
  2. Which circuits are backed up, and for how long under your actual evening load.
  3. The warranty, and what it is measured in: years, cycles, throughput, and what capacity is guaranteed at the end.
  4. Where it will be located, and whether that location complies with the installation standard and local code.
  5. Whether it can be added later to the inverter you are being quoted, if you decide not to buy one now.

If backup matters to you, say so before the design is drawn. Retrofitting backup capability to a system that was not designed for it is substantially more expensive than including it.

Also asked

Can I add a battery later?

Usually, either by adding a battery with its own inverter or by replacing the existing inverter with a hybrid. Which is cheaper depends on what was installed, which is why it is worth asking at the original quote even if you are not buying one — an inverter chosen with that in mind costs nothing extra today.

General information about solar and about hiring, not advice about your roof or your tax affairs. Incentives, net metering and contractor licensing are set federally, by state, and by your utility, and all of them change. The authority that publishes the rule is the current answer.