How do solar batteries work? Solar energy storage explained
Last updated 9/16/2021
With interest in energy storage technologies on the rise, it’s good to get a feel for how energy storage systems actually work. Knowing the way that energy storage systems integrate with solar panel systems–as well as with the rest of your home or business–can help you decide whether energy storage is right for you.
Below, we walk you through how energy storage systems work with solar and what that means for what you can expect to get from your storage system. We also take a more technical look at what exactly is happening inside of your battery to store that energy.
An overview of how solar batteries work step-by-step
At the highest level, solar batteries store energy for later use. If you have a home solar panel system, there are a few general steps to understand:
- Solar panels generate electricity from the sun
- This direct current (DC) electricity flows through an inverter to generate alternating current (AC) electricity
- The AC electricity powers your home appliances
- Extra electricity not used by your appliances charges your batteries
- When the sun goes down, your appliances are powered by the stored energy in your battery
How batteries works with solar panels
To understand how storage works with solar panels, it’s first worth a quick refresher of how solar panel systems work.
Typically, when you install solar panels, you’ll install a ‘grid-tied,’ net-metered solar panel system. This means that when your solar panels are producing more electricity than you need, you can export that excess electricity back to the grid and, conversely, you can pull electricity directly from the grid when you are using more electricity than your panels are producing. Net metering works by allowing you to run your electricity meter in reverse when you put extra energy onto the grid and run it forward when you’re pulling from the grid, with your utility billing you on net for the electricity you use.
With a solar plus storage system, instead of exporting any excess solar production to the grid, you can first use that electricity to charge your energy storage system. Then, when you’re using electricity after the sun’s gone down, you can draw from your solar battery instead of from the electric grid.
What you get with a solar plus storage system
When you install a battery with your solar panel system, you’ll have the ability to pull from either the grid or your battery, when it’s charged. This has two major implications:
Batteries provide backup power
Even though you’ll still be connected to the grid, you can operate “off-grid” since pairing solar plus storage will create a little energy island at your home. So in the event of an outage, either due to extreme weather or a utility shutoff, you’ll still be able to keep your lights on.
Two things to note about backup power. First, if you just have a solar panel system without a battery, you will not have power in the event of an outage, even if it’s a sunny day. This is because your solar panel system will shut down in the event of a power outage so that it doesn’t send electricity onto transmission lines while utility workers are attempting to fix them, which would pose a safety risk.
Second, most batteries only provide backup power for part, not all, of your home. Unless you also install a smart electrical panel with your battery (which is a great way to get the most out of a storage system), most battery installations will require you to select what parts of your home you want to back up with the battery, and pull those loads onto a critical load panel. However, many batteries can be “stacked”, meaning you can keep adding additional batteries until you have the storage capacity you want. So while it might be possible to achieve whole-home backup, it can be cost prohibitive to purchase enough batteries to provide that level of backup.
Batteries can help you avoid high utility rates
By allowing you to pull from your battery instead of from the electric grid, pairing a storage system with your solar panels can help you to avoid high utility rates. There are two ways batteries can do this. First, if you are on a time of use or other time-varying rate, you can pull from your battery at the times when your utility charges more for electricity, i.e., during peak hours. And, second, if you are on a rate with a demand charge, which is more typical for commercial and industrial companies than for homeowners, a battery can help you lower your demand charge each month, which is a significant financial benefit.
How batteries store energy
Now that you know how storage works with solar, you are perfectly well equipped to make the decision of whether or not to add storage to your solar panel system. But if you’re interested in also learning about the specifics of how batteries actually store energy, read on.
How lithium ion batteries work
The most typical type of battery on the market today for home energy storage is a lithium ion battery. Lithium ion batteries power all sorts of every-day appliances, from cell phones to cars, so it’s a very well understood, safe technology.
Lithium ion batteries are so called because they work by moving lithium ions through an electrolyte inside of the battery. Since ions are particles that have gained or lost an electron, moving the lithium ions from an anode to a cathode produces free electrons, i.e., electrons that have been released from lithium atoms. The build up of these free electrons is how batteries ultimately charge and store electricity. When you discharge the electricity stored in the battery, the flow of lithium ions is reversed, meaning the process is repeatable: you can charge and discharge lithium ion batteries hundreds or even thousands of times.
Lithium ion batteries used in home energy storage systems combine multiple lithium ion battery cells with complex power electronics that control the performance and safety of the whole battery system. There are several different types of lithium ion batteries that use slightly different chemistries to offer varied attributes, from improved power density to longer lifetimes.
Notably, lithium ion batteries aren’t the only type of battery used in energy storage applications at the home, business or utility level. The other types of batteries store energy via similar mechanisms, with an entirely separate set of pros and cons.
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