Why You Can Trust CNET Solar Battery Buying Guide: Everything You Need to Know
Want to go off the grid or earn energy bill credits? Adding a battery to a solar panel system may be the answer. Here's what you need to know.
Learn about whole-home battery backups to decide if they're right for you.
Full energy independence isn't achievable without solar batteries.
Solar panels can generate electricity only when the sun is shining. But with solar batteries, you can store that energy for use at night, during an outage or to sell it back to your utility or apply as bill credits.
Backup solar batteries run on electricity and can either work as a standalone device or as part of a home solar system. When the lights go out, your backup battery system will automatically switch on and serve as a source of electricity for several hours, a day or longer.
"If people have solar as well as a battery, they can use the solar in the day to feed their houses and charge their batteries. And at night, the batteries will serve their houses instead of the grid," Kim Quirk, a branch manager at ReVision Energy, told CNET recently. "It makes people a bit more independent from the grid when we tend to see big spikes."
However, all of these benefits come at a cost. Installing a battery backup system can be a significant investment, so it's important to understand what's involved. For this guide, we've answered some of the most common questions about battery backup systems, including how they work, how they're made, how much they cost and where you can buy them.
How solar batteries work
When your home doesn't need all the energy being produced by your solar panels, the excess energy is stored in the battery. When the solar panels aren't generating enough energy to fill the power needs of the building, the battery discharges reserve power to make up the difference.
The way you configure your solar battery system affects how it works. You have three main options:
Connect to your solar panels: Batteries connected to solar panels will fill and discharge frequently in response to the times without sun that you still want electricity. This is useful when in an area that is "off-grid," away from electrical utilities.
Connect your solar panels to a solar battery system and to the grid: You can choose to fill your battery and just keep it as a backup, rarely discharging it, and mostly selling and buying excess electricity from the electric company.
Use battery during time of use rate spikes: If you live in an area where electricity rates vary with the time of day, you can configure your system to use battery backup at the most expensive times and to buy electricity from the grid at the least expensive times.
Benefits and drawbacks of battery backup systems
Whether you have solar panels or not, battery backups offer plenty of benefits. For starters, they help you gain energy independence, so you don't have to rely on the public power grid. This is especially critical if you live somewhere with frequent outages or blackouts.
On top of that, battery backups don't operate on fossil fuels and provide your home with clean energy. Unlike generators, they're nearly silent to run and don't emit carbon into the atmosphere.
Even if the power hasn't gone out, you can use your battery backup as a way to save money on your electric bills. For example, if you're on a time-of-use utility plan, you can draw on the energy from your battery during peak hours rather than paying sky-high electricity rates to your energy company.
Pros of solar batteries
- Energy independence
- Save money on energy bills
- Less or no reliance on utility
- Power your home during an outage
- Clean energy
Cons of solar batteries
- Expensive, sometimes as much as a solar system
- High upfront costs
- Limited capacity
Different types of solar batteries
There are several kinds of batteries used in battery backup systems, including lithium-ion, lead-acid and flow batteries. Here's a quick overview of each type.
Lithium-ion batteries
Lithium-ion batteries are the most common for home systems. Most of today's popular battery backup products are lithium-ion, including the Tesla Powerwall, Panasonic EverVolt and Generac PWRcell. They're lightweight and energy-efficient, making them perfect for home use.
Lead-acid batteries
Lead-acid batteries have been used for hundreds of years and are the primary type of battery used in cars. They're cheaper than lithium-ion, but they aren't as efficient, which means they're best suited for small systems.
Flow batteries
Flow batteries (or redox flow batteries) are less common in home systems since they're mainly designed for commercial use. However, the technology appears promising, and it could become more widely used in residential battery backup systems in the near future.
Nickel-cadmium batteries
Nickel-cadmium batteries have a high energy density with double the energy of a lead-acid battery. Nickel-cadmium batteries are very durable, expensive and work well in extreme temperatures making them a good choice for large-scale commercial and industrial projects. Cadmium is toxic, however, and generally not appropriate for residential use.
Buying a backup battery system
You can get battery backups from a range of businesses, including manufacturers, solar companies and battery retailers. CNET curated a list of the best batteries here. The price will depend on which battery model you choose and how many you buy for your system. According to the US Department of Energy, solar batteries can cost anywhere from $12,000 to $22,000.
If you're buying a battery backup as part of a solar panel system, however, you may qualify for a rebate or tax credit.
How to set up a battery backup system
Once you've decided on a battery or batteries, make sure to have it professionally installed -- otherwise, you run the risk of injuring yourself. You can expect to pay a few thousand dollars for installation (which is separate from the cost of the battery).
Maintaining a battery backup system
After the initial setup, there's little maintenance required on a battery backup system. You won't need to replenish a fuel source (like you would with a generator), and there's no need for regular maintenance.
Lifespan and warranties
A few years after installation, you may notice that your battery backup system doesn't hold a charge as well as it used to. That's because, like other types of batteries, battery backups lose storage capacity over time.
To account for this, battery backups include a warranty that expresses how efficient the battery should be by the end of the warranty period. Many of the top solar batteries offer 10 years and 70%, meaning that by the end of the 10-year warranty, the battery should still operate at 70% of its original performance.
Inverters and batteries
Inverters play an important role in how the battery stores and converts solar energy. While solar panels generate electricity in direct current, or DC, the electric grid and homes generally use alternating current, or AC. An inverter can convert AC to DC or vice versa, and most solar batteries include an inverter to store the energy in DC form, as well as an inverter to convert it back into AC to be used in the grid or the home.
Because inversion of current isn't perfectly efficient, battery producers are always experimenting with how to invert less often and increase the efficiency of the battery. As a result, some batteries will not have inverters for both input and output included in the system. Talk to your solar installer about the battery system you're considering so that you can make sure you have all the external inverters you need.
FAQs
Why do I need a battery with solar panels?
Solar power is only available for part of the day. Adding a solar power storage battery system ensures you always have power when the sun isn't out.
Can I install my own solar battery?
A professional solar electricity system installer can help you select a battery that works well with your goals, whether you want to be entirely off-grid, have an emergency store for outages or minimize your costs from the electric company during peak hours.
Do solar batteries qualify for the federal tax credit?
Yes. The 30% federal solar tax credit can be applied to the total cost of your solar battery system if your battery can hold at least three kilowatt-hours of energy and is installed in 2023 or later.
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