Some models can be stacked to increase their power output, while for others, that’ll only increase their capacity. The Enphase IQ batteries, for example, scale: while one delivers 3.84 kW, two together will output 7.68 kW.
3. How much flexibility do I want?
If you plan to use a battery during power outages, then keep in mind that you’ll generally need to choose which four to seven appliances or “loads” might be critical to keep on. If you’re ready to decide now and don’t plan to change them, then your contractor will hard-wire them into a critical-loads panel.
“Only the loads that are on that panel can be backed up by your battery,” said Emily Walker, the senior writer at EnergySage who leads its consumer education strategy.
But there’s an alternative: smart panels. These devices “can help you dynamically shift your load so that you don’t have to decide from the start exactly what you want to back up,” Walker said. Options include products from startups Span, Lumin, and Koben and multinational corporation ABB in partnership with Lumin.
A home energy management system also allows you to more easily participate in programs that pay customers to send power to the grid, explained Bazhinov, founder and president of Lumin. When the grid is stressed, a smart panel can pause flexible loads for a couple of hours, like charging your EV or running your dishwasher, thereby minimizing what you consume yourself and maximizing energy exports. That allows you to get paid more.
Smart panels aren’t cheap, however. They can cost $2,500 to $3,500 for the equipment alone, with installation adding on another $1,000 to $1,500, depending on the complexity of the work and the local labor market, according to Spencer Fields, director of insights at EnergySage.
4. What other battery system hardware might I need?
Another factor to keep in mind is that if you want to use your battery during a blackout, it’ll need to be able to disconnect from the grid. If your home can’t “island” itself, your solar panels and battery will push power back into those lines — with potentially fatal consequences: Lineworkers who assume that the lines are dead can get electrocuted.
To sever the grid connection, you’ll need a transfer switch. “If there’s no power coming from the utility,” Cinnamon explained, “you hear this ka-chunk” as it physically disconnects. The price of that independence can come at around $3,000 to $4,000, he noted.
5. What type of battery should I get?
Though lead-acid batteries will work, the most popular batteries to pair with solar have lithium-ion chemistries that make them more energy dense and longer-lived. Two lithium-based chemistries dominate: lithium nickel manganese cobalt oxide, called NMC, and lithium iron (Fe) phosphate, called LFP.
NMC is today’s most common battery chemistry, but LFP is gaining popularity, Hadlow said. LFP batteries are less energy dense and tend to cost more per kWh, but they are more stable, and thus safer; are longer lasting (up to 20 years of daily use); and don’t put out as much heat, so they can be installed indoors with basically no risk, Walker said. Another battery chemistry to put on your radar: lithium titanate (LTO), she added. With a higher price point, LTO batteries are reputed to be even safer and longer-lived than LFP batteries.
6. Does the battery system I’m interested in have a good warranty?
Battery warranties usually cover the equipment (though not installation) cost of replacing a battery if it malfunctions within a certain number of years, a total energy throughput, or a number of cycles — the number of times a battery recharges after dipping below a certain threshold — whichever comes first. Manufacturers usually warranty a lithium-ion battery for at least 10 to 12 years. As a battery ages, its capacity also degrades. Manufacturers may specify how much energy you can expect the battery to still be able to store at the warranty’s end. Look for at least 60%, according to Fields.
7. Where am I putting a battery system?
You’ll want to make sure the battery you get is suited to where you install it. Some battery enclosures aren’t rated to withstand the elements and need to be placed indoors. Just make sure the installation complies with building and fire codes, Fields said. And for outdoor batteries, you don’t want to put them in direct sun, which could make them overheat.
The local environment may also influence what battery you choose and where you plonk it: If you live near the beach, salt water can corrode a battery’s casings, voiding the warranty. Other batteries can’t handle the high altitudes of the Rocky Mountains. For a well-reviewed installer, this won’t be their first rodeo; you can lean on them to recommend batteries well suited to your locale.
Taking the next step
If and when you’re ready to shop around for a home battery, remember to get at least three quotes, Walker said. The EnergySage marketplace provides them for free.
While home batteries carry big price tags, they might be worth it for you. If you have solar, they let you soak up every watt of clean power you generate — and that can pay dividends in lower energy bills, enhanced resilience, and a cooler climate.
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