Solar battery backup: What it costs and how to size it

Power outages are getting longer and more common. The average American household experienced about 11 hours of outage time in 2024, according to the U.S. Energy Information Administration (EIA), and that number keeps growing. Not only that, but power outages can cost up to $25,000 if property damage is involved.

If you've lost power during a heat wave, a winter storm, or a hurricane, you already understand the appeal of having solar battery backup. Solar panels alone won't keep the lights on, and a gas-powered generator is loud, needs fuel, and requires regular maintenance. Pairing solar panels with a home battery lets you store energy from your panels to use to keep your home up and running through days-long outages. 

It's not magic, and it's not cheap. But for the right homeowner, it can be worth every penny.

Solar battery backup combines rooftop solar panels with a home battery (often called a solar battery or energy storage system). so your home has power even when the grid doesn't. The panels generate electricity during the day, and any extra that you don't use immediately is stored in the battery. When the grid goes down, the system automatically switches to "island mode," disconnecting from the grid and drawing on the battery instead. You can also program your battery to kick on at night or on severe weather days when your solar panels aren't producing to lower the amount of energy you're drawing from the grid.

Some battery systems are designed for whole-home backup, keeping everything in your house running during outages. Others are set up for "essential loads" which means they power only your most critical circuits (i.e., refrigerator, lights, Wi-Fi router, medical equipment). The right setup depends on your energy needs and budget.

If you already have solar panels, you can add a battery or multiple batteries to your system. This is called a battery retrofit, and it's an increasingly popular option for homeowners who want emergency backup power or want to save on their electric bills.

On a normal sunny day, your solar panels produce electricity, your home uses what it needs, and any extra either charges your battery or flows back to the grid. During an outage, a solar panel system will automatically disconnect from the grid (a required safety feature to prevent utility workers from being electrocuted) and switches to island mode. At that point, your battery becomes your power source.

During daylight hours, your solar panels will continue to generate power and recharge your battery, which means a well-designed backup solar power system can run for days as long as the sun is shining. At night or during extended cloudy weather, you're using the energy stored in the battery until it's depleted.

A typical 13.5 kWh home battery—the size of a Tesla Powerwall 3, and roughly what a household needs to keep essentials running—costs $15,647 installed before incentives on average, based on EnergySage Marketplace data from the first half of 2026. Prices vary a lot by brand: some budget options run under $500 per kWh of storage, while premium brands can top $3,000 per kWh.

If you're pairing a battery with new solar panels, expect the combined system to run around $46,700 on average—about $31,000 for a 12 kW solar array plus roughly $15,650 for the battery, per EnergySage data. Retrofitting a battery onto solar you already own typically costs a bit more per unit, since the electrician has to work around your existing setup rather than wiring everything at once, so it's best to install both at the same time if feasible.

The number of batteries you need comes down to one question: what are you trying to protect against? EnergySage generally breaks this into three goals, and each calls for a different amount of storage.

Here's a rough way to run the numbers yourself:

• Add up the wattage of what you want to power

• Multiply by how many hours you'll run it

• Convert to kilowatt-hours.

Say you're running a 150-watt fridge, 50 watts of LED lighting, and a 10-watt Wi-Fi router around the clock. That's about 210 watts of continuous draw, or roughly 5 kWh per day—well within what a single fully charged battery can cover for two to three days on its own, and indefinitely with even modest solar production layered in.

Want to run something power-hungry, like central AC or a washer and dryer? You'll need to size up. Two to three batteries, plus enough solar panels to help recharge them, is the realistic starting point.

A lot of homeowners think that a single battery is a stand-in for your entire electrical panel—it's not. A 13.5 kWh battery can power an entire home for roughly 11 hours and 25 minutes, assuming the U.S. average daily energy use of 28.5 kWh.

A single 10–13.5 kWh battery can typically run these simutaneously:

• Refrigerator and freezer

• LED lighting

• Wi-Fi router and phone chargers

• A laptop or TV

• A sump pump (intermittently)

• Medical equipment like a CPAP machine or oxygen concentrator

It usually can't handle, without adding more capacity:

• Central air conditioning or electric heat

• A heat pump

• An electric clothes dryer

• An electric range or oven

• A well pump running continuously

• EV charging at the same time as everything else

That's why most battery installations route through a critical loads panel—a secondary panel that isolates just the circuits you've chosen to protect, so you don't accidentally overload a battery by running the AC and the dryer at the same time during an outage. Some newer systems use smart load-management software instead, which lets you back up more of your home without a dedicated panel by automatically shedding lower-priority loads when demand spikes.

For a more detailed look, check out our guide on how long you can run your house on a Tesla Powerwall. (Even if you're getting a different brand, most of them are around 13.5 kW, so the math should still work.

Generators have been the default backup power option for decades, and for homeowners on a tight budget, they still make sense in most cases. But there’s a reason many homeowners are ditching their gas generators for solar and battery systems. Kris, the founder of City Prepping—a home preparedness community—told EnergySage that he believes having solar and batteries is a far better solution for long-term emergency backup.

“Once you run out of whatever fuel source a generator needs—diesel, propane, natural gas—you're done. It's pretty much a paper weight at that point, unless you can get access to fuel,” said Kris. “As long as you learn how to manage and ration your power usage, solar and a battery is going to be easily your best option.”

A gas or propane generator is cheaper upfront—typically $500 to $5,000 for a portable unit or $7,000 to $15,000 for a whole-home standby model. But you're on the hook for fuel, storage, regular maintenance, and the noise and toxic fumes that come with running one.

Over a 20-year span, EnergySage's modeling puts the total cost of a solar-plus-storage system (including the electricity it generates) at roughly $62,300, compared to about $91,300 for a 10 kW propane generator once you factor in fuel and replacement costs. The generator wins on upfront price. The battery tends to win over time, especially if it's paired with solar panels doing double duty on your electric bill.

For many homeowners, it comes down to how often and how long outages hit your area. Occasional, short outages might not justify a full battery system. Frequent or multi-day outages from severe weather or an aging grid make the case for solar battery backup much stronger.

While the federal residential solar Investment Tax Credit (ITC) for solar-plus-battery systems expired in 2025, many states and utilities offer their own rebates, tax credits, and demand-response programs for solar, battery, and combination systems. It's worth researching what's available in your area or asking a reputable solar contractor to find incentives for you.

The best first step is to get quotes from local solar installers who have experience designing backup systems. Not all solar companies specialize in storage, so ask directly whether they've completed solar-plus-battery projects in your area.

When you're comparing quotes, look closely at:

• Battery capacity (kWh) and whether it matches your ideal backup goal

• Which circuits are included on the critical loads panel or smart panel

• Inverter type—some hybrid inverters support both solar and battery, which can simplify your system and often lower the cost

• Warranty terms for both the panels and the battery, single batteries typically carry shorter warranties and likely will need to be replaced before your panels.

Sign up to see free quotes from pre-vetted installers on the EnergySage Marketplace. If you let them know you're interested in battery backup, they'll include storage options in their proposals so you can compare apples to apples. Our Energy Advisors are also available at no-cost to help you sort through the quotes and make sure you're not paying more than you should.

Whether solar battery backup is worth it for your home depends on how often your power goes out, what you can't afford to lose when it does, and how much you're willing to spend for that peace of mind. For a lot of homeowners in outage-prone areas, it's a clear yes. For others, a small battery might do the job just fine.