What are gravity batteries and how do they work?


Gravity batteries store energy using gravity. They are often used to store energy from renewable sources such as solar and wind energy. For example, a gravity battery might use solar energy to pump water uphill on a sunny day, and then, on a cloudy day, let the water flow down (using gravity) and generate power from it hydroelectrically.

The biggest problem with renewable energy is that when sunlight or wind disappears, so does the energy. You need batteries to store the extra energy for those times, but not all “batteries” have to be chemical: just use gravity!

The curse of abundance

Suppose you have not kept pace with the advancement of renewable energy solutions such as solar energy. In this case, you might think that the main challenge is getting enough power from solar and wind power, but often the other way around.

When your renewable energy source generates more energy than you need, you either have to use it or lose it. This is why grid-tied solar home installations can put power back into the grid, and you can even get paid for it!

Off-grid home solar installations use battery arrays to store excess energy so that it can be used at night or when it’s cloudy. Deep-cycle lead-acid batteries are popular for this use, but lithium-based solutions like the Tesla Power Wall are a better solution these days.

Whether it’s lead acid or lithium, these batteries store energy using an electrochemical process, but what if you could store and release energy without the need for an electrolyte?

Gravity batteries have potential (energy)

This is where the idea of ​​a gravity battery comes in. Gravity is that force that keeps us firmly on the ground. That is why “what flies up must come down.” Overcoming gravity requires a huge amount of energy. You need a chemical rocket the size of a building to launch a relatively small spacecraft with a few astronauts on board into orbit.

When you lift something on a table, the calories you burn to lift it are converted into potential energy now stored in that body. If your cat hits that object off the table later, that potential energy will be released when the object falls back to the ground.

A gravity battery converts this potential energy into electricity, but there are many different ways to convert potential energy into electrical energy.

Different types of gravity batteries

Gravity diagram showing stored wind energy using weights acting in a column

The most common example of a gravity battery today is also one already in common use. Energy companies pump water into elevated reservoirs to store energy. Later, when they want to access this energy, the water is released and flows into another tank, flowing through a hydroelectric turbine before getting there. These water pump turbine systems work well, but there are only so many places you can build them, not to mention that they don’t actually shrink in a useful way.

There are companies like Gravitricity that build large gravity batteries that can be installed anywhere, unlike water tank solutions. Their display platform uses two 25-tonne weights in a 15-meter (49.21-foot) platform to supply 250 kilowatts of power. The company claims that its technology can reach 20 megawatts and that the design life of its systems is up to 50 years.

The advantage of these systems is that you can produce a lot of energy in a short time or small amounts over long periods. It’s also a great way to ensure you have power if your renewables are experiencing a transient drop since it takes less than 1 second to reach full power output. Most importantly, it works cheaper in the long run than lithium battery formulations that provide similar performance, so it caught the attention of renewable energy producers!

On a small scale, there are products like Gravity Light (now defunct) where weightlifting provides about 20 minutes of light and eliminates the need for dangerous kerosene lighting.

Gravity batteries are potentially a key component of a practical and sustainable renewable energy grid due to their simplicity and potential longevity.

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