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How Does A Solar Battery Work? | Energy Storage Explained

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A lithium-ion battery, the most popular battery technology for solar battery energy storage.
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A solar battery can be an important addition to your solar power system. It helps you store excess electricity that you can use when your solar panels aren't generating enough energy, and gives you more options for how to power your home.

If you’re looking for the answer to, “How do solar batteries work?”, this article will explain what a solar battery is, solar battery science, how solar batteries work with a solar power system, and the overall benefits of using solar battery storage.

What is a Solar Battery?

Let’s start with a simple answer to the question, “What is a solar battery?”:

A solar battery is a device that you can add to your solar power system to store the excess electricity generated by your solar panels.

You can then use that 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.

The point of a solar battery is to help 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, which means you're generating power and providing it to other people without taking full advantage of the electricity your panels create first.

For more information, check out our Solar Battery Guide: Benefits, Features, and Cost

The Science of Solar Batteries

Lithium-ion batteries are the most popular form of solar batteries currently 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 prefer lithium-ion batteries because they can store more energy, hold that 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

As mentioned earlier, 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 at pocket-friendly prices, their popularity is fading due to low DoD and shorter lifespan.

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 that the solar panels create.

Solar cells create DC electricity, and that 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 does result 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 that it can store energy from both solar panels and the grid. This means that 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:

  1. Sunlight hits the solar panels and the energy is converted to DC electricity.
  2. The electricity enters the battery and is stored as DC electricity.
  3. The DC electricity then leaves the battery and enters an inverter to be converted into AC electricity the home can use.

The process is slightly different with an AC-coupled system.

  1. Sunlight hits the solar panels and the energy is converted to DC electricity.
  2. The electricity enters the inverter to be converted into AC electricity the home can use.
  3. Excess electricity then flows through another inverter to change back into DC electricity that can be stored for later.
  4. If the house needs to use the energy stored in the battery, that electricity must flow 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 can also convert AC electricity into DC electricity. As a result, you don't need two inverters in your photovoltaic (PV) 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. It eliminates the need to have two separate inverters in the same setup by functioning as an inverter for both the electricity from your solar battery and the electricity from your solar panels.

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 backup 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 can often produce 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.

Reduces Your Carbon Footprint

With solar panel battery storage, you can go green by making the most of the clean 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 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 much-needed power if you don’t have any 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.

A Quiet Solution to Backup Power Needs

A solar power battery is a 100% noiseless backup power storage option. You get to benefit from maintenance free clean energy, and don’t have to deal with the noise that comes from a gas-powered backup generator.

Key Takeaways

Understanding how a solar battery works is important if you’re thinking about adding solar panel energy storage to your solar power system. Because it operates like a large rechargeable battery for your home, you can take advantage of any excess solar energy your solar panels create, giving you more control over when and how you use solar energy.

Lithium-ion batteries are the most popular type of solar battery, and work through a chemical reaction that stores energy, and then releases it as electrical energy for use in your home. Whether you choose a DC-coupled, AC-coupled, or hybrid system, you can increase the return on investment of your solar power system without relying on the grid.

Having the right system design is vital to making the most of your solar panels and batteries. At Palmetto, we have the expertise and experience to guide you on your clean energy journey. From solar power installation and service to energy storage and monitoring, our solar professionals are here to help you take advantage of clean energy.

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