Batteries

Solar batteries work by storing energy produced by your solar panels for later use. In some cases, solar batteries have their own inverter and offer integrated energy conversion. The higher your battery's capacity, the more solar energy it can store.

When you install a solar battery as part of your solar panel system, you are able to store excess solar electricity at your home instead of sending it back to the grid. If your solar panels are producing more electricity than you need, the excess energy goes towards charging the battery. Later, when your solar panels aren’t producing electricity, you can draw down the energy you stored earlier in your battery for night use. You’ll only send electricity back to the grid when your battery is fully charged, and you’ll only draw electricity from the grid when your battery is depleted.

What this means in practical terms is that homes with solar-plus-storage can store excess solar power onsite for use later when the sun isn’t shining. As a bonus, since solar batteries store energy at your home, they also offer short-term backup power in the event that there’s a power outage in your area.
While batteries are typically paired with home solar energy systems, they can also be useful to homeowners without solar panels. Small-scale energy storage, the technology used in solar-plus-storage systems, can also be charged with electricity from the grid to provide backup power without the use of a diesel-powered backup generator.

Whether you can save money by installing a solar battery depends on the way that your utility compensates you for your solar power. Most utilities offer full net metering, which means that you receive a credit on your electric bill for every kilowatt-hour of electricity your solar panels produce (even if you don’t use them immediately). This means that you won’t see additional savings on your monthly electricity bill if you install a solar battery.

However, there are many situations where a solar battery can improve the economics of solar panels for your home or business. If your utility has time-of-use rates or demand charges, or does not offer net metering, solar batteries can help you save more when you go solar.

As you consider your solar-plus-storage options, you’ll come across a lot of complicated product specifications. The most important ones to use during your evaluation are the battery’s capacity & power ratings, depth of discharge (DoD), round-trip efficiency, warranty, and manufacturer. Capacity is the total amount of electricity that a solar battery can store, measured in kilowatt-hours (kWh). Most home solar batteries are designed to be “stackable,” which means that you can include multiple batteries with your solar-plus-storage system to get extra capacity. 

Most solar batteries need to retain some charge at all times due to their chemical composition. If you use 100 percent of a battery’s charge, its useful life will be significantly shortened. 

The depth of discharge (DoD) of a battery refers to the amount of a battery’s capacity that has been used. Most manufacturers will specify a maximum DoD for optimal performance. For example, if a 10 kWh battery has a DoD of 90 percent, you shouldn’t use more than 9 kWh of the battery before recharging it. Generally speaking, a higher DoD means you will be able to utilize more of your battery’s capacity. 

For most uses of home energy storage, your battery will “cycle” (charge and drain) daily.
For example, a battery might be warrantied for 5,000 cycles or 10 years at 70 percent of its original capacity. This means that at the end of the warranty, the battery will have lost no more than 30 percent of its original ability to store energy.  


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