Solar Batteries and Backup Power: Do You Need One?

New England storms take the power out, and many homeowners going solar want to know whether their panels will keep the lights on. On their own, they won't. With a battery, they can.

Whether a battery is worth adding depends on how often you lose power, what you need to keep running, and which state program you can join. This guide covers what a battery does, how long it lasts, how to size one, what Massachusetts, Connecticut and Rhode Island pay battery owners, and how a battery compares with a generator.

What does a solar battery do?

A home battery stores electricity so you can use it later. Most are lithium-ion, like a much larger version of the battery in your phone. Paired with solar, a battery does three jobs:

• Backup power. When the grid goes down, the battery powers your home and your panels recharge it during the day.
• Earning from battery programs. Utilities pay battery owners to send stored power to the grid on the hottest summer afternoons, when demand peaks.
• Using more of your own solar. The battery charges from your panels during the day and runs your home in the evening.

That last job matters less here than in some other states. Massachusetts, Connecticut and Rhode Island all credit the extra power your panels send to the grid, so the grid already acts like a battery for your bill. Our original guide to how solar panel batteries work covers the basics, and how net metering works explains the credits.

Do you need a battery with solar panels?

Most homes don't need a battery to save money with solar. The savings come from the panels and net metering. A battery is an add-on you choose for what it gives you on top of that.

The question to ask isn't only "do I need one?" but "what would a battery be worth to my household?" A home that loses power a few times a winter, or can't risk losing it at all, answers that differently from one that rarely notices an outage.

What happens to solar panels in a power outage?

A grid-tied solar system without a battery shuts off when the power goes out. That's a safety rule: it keeps your panels from sending electricity onto lines that utility crews are repairing. It surprises a lot of homeowners, who expect panels on the roof to keep the lights on.

A battery changes that. When the grid goes down, the system separates from it and powers your home from the battery. During the day, the panels recharge the battery, so a sunny day in the middle of an outage refills what you used overnight. When the grid comes back, the system reconnects on its own.

How long will a solar battery power your house?

Two numbers describe a battery. Capacity, in kilowatt-hours (kWh), is how much energy it stores. Power, in kilowatts (kW), is how much it can deliver at once, which decides whether it can start something big like a well pump or central air.

How long it lasts depends on what you run. As a rough guide, a battery holding 10 kilowatt-hours could run essentials drawing about 1 kilowatt for around 10 hours. Run an electric dryer, an electric range and central air at the same time and it drains far faster.

What helps a battery last through an outage:

• Back up essentials, not everything. Refrigerator, lights, Wi-Fi, outlets for phones and a furnace fan or boiler.
• Let the sun refill it. Solar recharges the battery every day, so even winter days add energy back.
• Save big loads for daytime. Run the washer or well pump while the panels are producing.

What size battery do you need?

Sizing starts with a decision: what do you want to keep running?

• Essentials backup. The battery powers a separate panel wired with your most important circuits. It's the most common choice and needs the smallest battery.
• Whole-home backup. The battery can run the entire house, which takes more capacity, more power output, or more than one battery, especially for well pumps, heat pumps or central air.

Your installer works it out from your electric bill, the circuits you want covered, and any large motors that need extra power to start. If you're planning an electric car or a heat pump, say so, because both change what a battery needs to handle. The design should show the capacity, the power output and which circuits are covered.

Which programs pay you to have a battery?

Utilities in all three states pay battery owners to send stored power to the grid during peak summer demand. The payments help cover the cost of the battery, and utilities try to avoid calling events when big storms are forecast.

Program rules and rates change, so your installer should confirm the current terms when you enroll. In Massachusetts, SMART 3.0 doesn't add a storage bonus for home-sized systems, so the battery's value there comes from ConnectedSolutions and backup power. Our guides to SMART 3.0 and the Rhode Island solar grant cover the solar side.

How do you pay for a solar battery?

A battery can be bought with your solar system or added to it, and there are several ways to pay:

• With your solar financing. A battery can be part of the same loan as the panels.
• Mass Save HEAT Loan (Massachusetts). 0% financing up to $25,000 for batteries, though not for the panels themselves.
• Smart-E Loan (Connecticut). The Connecticut Green Bank's loan covers solar panels and batteries. Our guide to solar loan programs in Massachusetts and Connecticut has the details.
• Rhode Island grant bonus. The Renewable Energy Fund grant adds $5,000 when a battery is funded together with an owned solar system.
• A lease or PPA. A battery that's part of a lease or PPA can still qualify for the 30% federal credit, which lowers what you pay.

If you're paying cash or using a loan, note that the 30% federal homeowner credit, which used to cover batteries, ended for systems installed after December 31, 2025. State programs now do that work instead. Our guide to solar financing compares every way to pay.

Batteries we install as part of an Evergreen Solar system are covered by the same 25-year warranty as the system, so the battery and the panels are protected for the same stretch.

Should you get a battery or a generator?

Both keep the lights on in an outage. They suit different homes.

A battery fits homes with solar that want quiet, automatic backup for essentials and some return from a battery program. A generator fits homes that need to run heavy loads for days at a time. Some homeowners keep an existing generator and add a battery for shorter outages.

Can you add a battery to solar later?

Usually, yes. Many batteries can be added to an existing solar system, and Massachusetts ConnectedSolutions accepts batteries installed with new or existing solar, or on their own. Your installer checks your inverter, your electrical panel and the space for the battery first.

There are reasons to decide at the start, though. Installing the battery with the panels means one design, one set of permits and one installation. And in Rhode Island, the grant's $5,000 battery bonus only applies when the battery is funded in the same award as the solar.

If you're not sure, ask for your quote both ways: solar on its own, and solar with a battery. Our guide to going solar, step by step shows where that choice fits in the process, and what solar costs and saves covers the numbers for the panels themselves.

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