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Energy storage and solar batteries: what you need to know

The concept of storage is as old as time itself. At the risk of sounding too much like Jared Diamond, civilization has only truly progressed in leaps and bounds when it’s been able to take something produced one day–crops, a meal, or even an idea–and store it for use at a later point in time.

Similarly, the notion of using a battery to store energy is so familiar to us as the AA and AAA cylinders that keep our TV remotes working, that most people spend very little time thinking about the role that batteries can play in keeping the lights on in your house, your neighborhood, or your whole state. But energy storage, and batteries in particular, have an important role to play in the clean energy future.

Below, we cover why energy storage is so important for clean energy. Already familiar with the role storage has to play or looking for an answer to a different question? In the rest of our Storage 101 section you’ll find everything you need to know about solar power storage for your home or business, how to decide if a battery is right for you and, if so, how to choose (and install) the right battery for your needs.

What is energy storage? What is a solar battery?

The primary function of solar energy storage is to store energy produced by solar panels that can be drawn on at a later time. Storing energy for later provides many benefits, from financial savings to being a backup source of power in the event of a grid outage.

The main advantage of installing a solar-plus-storage energy system is that it gives you the ability to use your solar electricity even when the sun isn’t shining. When you install a solar panel system without a home battery, the excess electricity that your system generates gets sent back to the grid. With solar energy storage, that energy can be stored and drawn on when the sun goes down, and you’ll only need to draw and pay for energy from the grid when your battery is depleted.

Are a battery and energy storage system the same thing?

Not necessarily! A battery is a form of energy storage, but not all forms of energy storage are batteries. In residential applications, the most common form of energy storage is with a battery, so the two terms are often used interchangeably; however, for commercial and industrial businesses, as well as for the electricity grid as a whole, energy storage frequently means a technology other than a battery, whether that’s pumped storage hydropower or fuel-cell-generated hydrogen.

Why are batteries so important for clean energy?

Batteries are a critical component of the clean energy future for one key reason: they are able to match variable energy supply to energy demand. Why this is so important requires a quick discussion of the differences between producing electricity with fossil fuels and producing electricity with clean energy resources, like wind and solar.

What the electrical grid is good at: generating electricity with fossil fuels

The electrical grid is the interconnected web of poles and wires that connects our homes and businesses to the power plants that produce the electrons that keep our lights on. Importantly, the electrical grid was designed to match electricity production to electricity demand. In other words, the grid excels at anticipating when and where electricity will be needed, generating the precise amount of electricity needed at that time (plus a bit extra for safety’s sake), and getting that electricity to exactly where it needs to be at exactly the point when it’s needed. Quite the delicate balance!

Originally, the most cost and resource efficient way to keep this delicate balance operational was to use fossil fuel-fired power plants, like coal and natural gas facilities. Put simply, when the electricity grid operator predicted more people would be using more electricity–like when every AC unit is cranking in the afternoon on the hottest day of the summer–they could call on coal or natural gas powered fire plants to produce more power by burning more coal or gas. And if those power plants were running at full tilt, the grid operator could call on another power plant and tell them to start burning fuel. The same principle works in reverse when electricity demand declines over night when everyone’s asleep: the grid operator can call and tell power plants to decrease the amount of electricity they produce.

When demand increases, the grid operator can increase supply. And when demand decreases, power plants adjust to lower their supply. Simply, adjusting supply to meet demand.

What the electrical grid is less good at: integrating renewable energy

Now consider a scenario where you can predict how much electricity your power plants will generate, but you can’t control when that will occur. In order to continue to provide electricity to people when they need it under this scenario, you need to either: 1) shift electricity demand to occur when your power plants are producing electricity, or 2) find a way to store electricity when it’s produced to use when demand exists.

At its core, this is exactly the scenario playing out with renewable energy technologies, and part of the reason why some grid operators have historically been reluctant to embrace renewable energy wholeheartedly. Solar produces electricity when the sun is shining, but produces no energy at night. Similarly, wind produces electricity when the wind is blowing, but not when all is still. We can predict how frequently and how strongly the sun will shine and the wind will blow, and can even predict how much electricity solar and wind can produce down to the minute far in advance. But we can’t shift the sun’s schedule or influence when the wind blows, meaning we can’t control when those resources produce electricity.

How energy storage helps renewable energy

This is where energy storage can play a major role in helping the grid to integrate more renewable energy resources; by storing the electricity that wind turbines and solar panels produce to use at a later time, energy storage can better shift electricity supply to meet demand. The ambitious clean energy goals and targets announced at the federal and individual state levels throughout the US can only be met with the help of energy storage.

Types of energy storage systems

Today, when people talk about energy storage, they typically mean batteries, especially when paired with a solar energy system. However, batteries are far from the only form of energy storage out there and they’re far from the first technology providing energy storage solutions to the electricity grid. That being said, the best and most applicable type of energy storage for most people is electrochemical, which is what you probably think of when you think of a solar battery.

Electrochemical storage

If you’ve heard about storage, or batteries, electrochemical storage is what you’re likely most familiar with. Electrochemical storage includes a number of different categories of batteries - from lithium ion to lead acid to even vanadium flow batteries. You’ll find these types of batteries everywhere: AA and AAA batteries are a form of electrochemical storage, as are the batteries in your cell phone and even the battery in your car.

With that in mind, you might be able to guess the primary benefit of electrochemical storage: how compact it is. These types of batteries can be made in all shapes and sizes and are extremely power dense, meaning they pack a lot of punch for their size. This makes electrochemical storage devices perfect for your home or business, which is why they’re typically paired with solar panel systems.

Gravitational storage

Energy storage has been providing benefits to the electrical grid for decades in the form of gravitational storage. The most common form of this is pumped hydropower storage: water is pumped uphill into a reservoir, and then released to run back downhill through a series of turbines to generate electricity. By pumping the water uphill at times when electricity is plentiful, inexpensive, or both, and running the water back downhill at times when there’s a shortage of electricity and/or it’s more expensive, pumped hydro can provide a useful service to the grid as a large-scale way to store excess electricity. The best known example of this technology is actually at Niagara Falls in Buffalo, NY.

It’s worth noting, though, that pumped hydropower isn’t the only form of gravitational energy storage. A number of innovative technologies aim to use a similar approach with different elements, like using pulleys to raise large heavy objects and then generating electricity by releasing those objects and letting them drop. Other similar technologies involve stacking blocks. Don't ask - we don't get it either.

Mechanical storage

Another early form of energy storage is mechanical storage. The most common type of mechanical storage is a flywheel. It’s not dissimilar to a wind-up toy: you store energy by winding up the toy (or flywheel), and then release energy by letting the toy (or flywheel) unwind. Flywheels have yet to gain much traction at a large scale, but have a number of applications given how quickly they can release energy.

Another form of mechanical storage is compressed air energy storage. Compressed air systems work exactly the way it sounds like they would: by compressing air. For a compressed air energy storage system to work, a company will pump air into a cavern to increase the pressure of the stored air. The system then produces electricity by slowly–or quickly!–releasing the pressurized air.

Thermal storage

It’s not just electricity that can be used in energy storage systems: you can also store thermal energy. For instance, you can pre-heat a hot water tank overnight when electricity demand and prices are low, so that there’s no need to heat the water in the morning when the whole world is waking up and getting ready to go to work, putting stress on the electrical system. The same thing can be achieved with ice blocks and cooling freezers, or even operating AC systems.

Creating hydrogen with fuel cells

One way to store energy for use later is to convert it into a liquid fuel, like hydrogen. Fuel cells convert electricity into a fuel, making it possible to convert solar or wind power into the type of fuel that can power industrial processes, like forklifts. The best part? There are no carbon emissions when you burn hydrogen. Though the deployment of fuel cells and hydrogen technologies has been limited so far, many people in the energy industry are very optimistic about the role that these technologies will play in a clean energy future.

Coming soon: seasonal storage

One type of energy storage technology under development is seasonal energy storage: not only storing large amounts of electricity, but storing it for long periods of time. Seasonal storage has the potential to revolutionize the way that renewable resources are integrated into the electrical grid. For instance, you can store excess solar energy produced during the summer to help serve load in the winter months when the sun isn’t shining as strongly.