Solar panels generate free and renewable electricity from sunlight. How do you maximize using the power your panels generate, as well as the savings on your utility bill? One way is with energy storage. Having solar battery backup can give you more energy independence and, in some areas, additional economic benefits.
We’ll explain more about solar batteries and energy storage to help you understand when adding a battery to your home is a good decision.
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What Is a Solar Battery?
A solar battery is a device you can add to your solar power system to store the excess electricity generated by your solar panels.
You can use the stored energy to power your home at times when your solar panels don't generate enough electricity, including nights, cloudy days, and during power outages.
A solar battery helps you use more of the solar energy you’re creating. If you don't have battery storage, any excess electricity from solar power goes to the grid. In some locations this might be the most economical way to use your solar energy. In others — or if your goal is to use as much of your solar power as possible — a solar battery can be a good fit.
The Science of Solar Batteries
Lithium-ion batteries are the most popular form of solar batteries on the market. This is the same technology used for smartphones and other high-tech batteries.
Lithium-ion batteries work through a chemical reaction that stores chemical energy before converting it to electrical energy. The reaction occurs when lithium ions release free electrons, and those electrons flow from the negatively-charged anode to the positively-charged cathode.
This movement is encouraged and enhanced by lithium-salt electrolyte, a liquid inside the battery that balances the reaction by providing the necessary positive ions. This flow of free electrons creates the current necessary for people to use electricity.
When you draw electricity from the battery, the lithium ions flow back across the electrolyte to the positive electrode. At the same time, electrons move from the negative electrode to the positive electrode via the outer circuit, powering the plugged-in device.
Home solar power storage batteries combine multiple ion battery cells with sophisticated electronics that regulate the performance and safety of the whole solar battery system. Thus, solar batteries function as rechargeable batteries that use the power of the sun as the initial input that kickstarts the whole process of creating an electrical current.
Comparing Battery Storage Technologies
When it comes to solar battery types, there are two common options: lithium-ion and lead-acid. Solar panel companies almost always install lithium-ion batteries because they can store more energy, hold energy longer than other batteries, and have a higher depth of discharge.
Also known as DoD, depth of discharge is the percentage to which a battery can be used, related to its total capacity. For example, if a battery has a DoD of 95%, it can safely use up to 95% of the battery’s capacity before it needs to be recharged.
Lithium-ion battery
Battery manufacturers prefer lithium-ion battery technology for its higher DoD, reliable lifespan, ability to hold more energy for longer, and a more compact size. However, because of these numerous benefits, lithium-ion batteries are also more expensive compared to lead-acid batteries.
Lead-acid battery
Lead-acid batteries (the same technology as most car batteries) have been around for years, and have been used widely as in-home energy storage systems for off-grid power options. While they are still on the market, their popularity is fading due to low DoD and shorter lifespan.
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AC-Coupled Storage vs DC-Coupled Storage
Coupling refers to how your solar panels are wired to your battery storage system, and the options are either direct current (DC) coupling or alternating current (AC) coupling. The main difference between the two lies in the path taken by the electricity the solar panels create.
Solar cells create DC electricity, and DC electricity must be converted into AC electricity before it can be used by your home. However, solar batteries can only store DC electricity, so there are different ways of connecting a solar battery into your solar power system.
DC-coupled storage
With DC coupling, the DC electricity created by solar panels flows through a charge controller and then directly into the solar battery. There is no current change before storage, and conversion from DC to AC only occurs when the battery sends electricity to your home, or back out into the grid.
A DC-coupled storage battery is more efficient, because the electricity only needs to change from DC to AC once. However, DC-coupled storage typically requires a more complex installation, which can increase the initial cost and lengthen the overall installation timeline.
AC-coupled storage
With AC coupling, DC electricity generated by your solar panels goes through an inverter first to be converted into AC electricity for everyday use by appliances in your home. That AC current can also be sent to a separate inverter to be converted back to DC current for storage in the solar battery. When it’s time to use the stored energy, the electricity flows out of the battery and back into an inverter to be converted back into AC electricity for your home.
With AC-coupled storage, electricity is inverted three separate times: once when going from your solar panels into the house, another when going from the home into battery storage, and a third time when going from battery storage back into the house. Each inversion results in some efficiency losses, so AC-coupled storage is slightly less efficient than a DC-coupled system.
Unlike DC-coupled storage that only stores energy from solar panels, one of the big advantages of AC-coupled storage is it can store energy from both solar panels and the grid. This means even if your solar panels aren’t generating enough electricity to fully charge your battery, you can still fill the battery with electricity from the grid to provide you with backup power, or to take advantage of electricity rate arbitrage.
It’s also easier to upgrade your existing solar power system with AC-coupled battery storage, because it can just be added on top of an existing system design, instead of needing to be integrated into it. This makes AC-coupled battery storage a more popular option for retrofit installations.
How Solar Batteries Work With a Solar Power System
This entire process starts with the solar panels on the roof generating power. Here is a step-by-step breakdown of what happens with a DC-coupled system:
- Sunlight hits the solar panels and generates DC electricity.
- Electricity enters the battery and is stored.
- DC electricity leaves the battery and an inverter converts it into AC electricity the home or the grid can use.
The process is slightly different with an AC-coupled system.
- Sunlight hits the solar panels and generates DC electricity.
- Electricity enters the inverter to be converted into AC electricity the home can use.
- Excess electricity flows through another inverter to change back into DC electricity that can be stored.
- When the energy stored in the battery is used, that electricity flows through the inverter again to become AC electricity.
How Solar Batteries Work With a Hybrid Inverter
If you have a hybrid inverter, a single device can convert DC electricity into AC electricity and AC electricity into DC electricity. As a result, you don't need two inverters in your photovoltaic system: one to convert electricity from your solar panels (solar inverter) and another to convert electricity from the solar battery (battery inverter).
Also known as a battery-based inverter or hybrid grid-tied inverter, the hybrid inverter combines a battery inverter and solar inverter into a single piece of equipment.
Hybrid inverters are growing in popularity because they work with and without battery storage. You can install a hybrid inverter into your battery-less solar power system during the initial installation, giving you the option of adding solar energy storage down the line.
Benefits of Solar Battery Storage
Adding battery storage for solar panels is a great way of ensuring you get the most out of your solar power system. Here are some of the main benefits of a home solar battery storage system.
Stores excess electricity generation
Your solar panel system often produces more power than you need, especially on sunny days when no one is at home. If you don't have solar energy battery storage, the extra energy will be sent to the grid. If you participate in a net metering program, you can earn credit for that extra generation, but it’s usually not a 1:1 ratio for the electricity you generate.
With battery storage, the extra electricity charges up your battery for later use, instead of going to the grid. You can use the stored energy during times of lower generation, which reduces your reliance upon the grid for electricity.
Provides relief from power outages
Since your batteries can store the excess energy created by your solar panels, your home will have electricity available during power outages and other times when the grid goes down. (In some locations, batteries are installed as arbitrage, or consumption-only, systems. These are cheaper to install and let you store energy for later use, but don’t provide backup power.)
Reduces your carbon footprint
With solar panel battery storage, you can go green by making the most of the clean, renewable energy produced by your solar panel system. If that energy isn't stored, you will rely on the grid when your solar panels don’t generate enough for your needs. However, most grid electricity is produced using fossil fuels, so you will likely be running on dirty energy and boosting your personal carbon footprint when drawing from the grid.
Provides electricity even after the sun goes down
When the sun goes down and solar panels aren't generating electricity, the grid steps in to provide needed power if you don’t have battery storage. With a solar battery, you’ll use more of your own solar electricity at night, giving you more energy independence and helping you keep your electric bill low.
Provides quiet backup power
A solar power battery is a quiet backup power storage option. You get maintenance-free clean energy, without the noise from a gas-powered backup generator.
When Battery Storage and Going Solar Make Sense
Understanding how a solar battery works is important if you’re thinking about adding energy storage to your solar power system. You can take advantage of the excess energy your solar panels create, giving you more control over when and how you use solar energy.
Having the right system design is vital to making the most of your solar panels. A system that’s designed, installed, serviced, and maintained well could help you lower your energy bills for decades to come. Reach out today to get a free estimate of your savings.
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Frequently Asked Questions
Is it worth getting batteries for solar?
In some cases, yes, having batteries for solar energy storage can be a valuable complement to your solar panels. Having battery storage lets you use solar power 24/7, maximize savings from your system, and have reliable power during bad weather and grid outages.
How many batteries do you need to run a house on solar?
This depends on your needs and how you expect to use your energy system. For short-term use of stored power or owners fine with using some grid electricity, one or two batteries is the likely answer. For owners going “off the grid” or expecting full or close-to-full power during major outages or disasters, stacks of batteries may be needed.
How long does a solar backup battery last?
Solar battery lifespans are 5-15 years. Major manufacturers often extend 10-year warranties for their batteries. You may be able to prolong your battery’s lifetime and long-term efficiency with smart usage habits.
How much does a solar battery backup system cost?
The cost of solar batteries varies quite a bit depending on the capacity and number of batteries you need and the incentives, such as tax credits and rebates, available to you. Home solar batteries can cost up to $15,000 to purchase and install.
Andrew GiermakWriter and EditorAndrew joined Palmetto in Charlotte in August 2024. He’s been a writer in journalism, then in business, going back to almost the 20th century. He’s lived in Indiana, Virginia, Pennsylvania, Virginia again, and now North Carolina for the last 12 years. He likes golf. Is he good at it? Not so much.
