What Are Gravity Batteries, and How Do They Work?

Gravitricity

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

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

The Curse of Plenty

Suppose you haven’t been keeping up with the advancement of renewable energy solutions such as solar power. In that case, you may think that the main challenge is getting enough power out of solar and wind, but it’s often the opposite.

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

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

Whether lead acid or lithium, these batteries store energy using an electrochemical process, but what if you could store and release power without needing 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. It’s why “what goes up must come down.” Overcoming gravity takes a massive amount of energy. You need a building-sized chemical rocket to launch a relatively small spaceship with a few astronauts on board into orbit.

When you lift an object onto a table, the calories you burn to lift it are converted into potential energy, now stored in that object. If your cat knocks that object off the table later, that potential energy is released as the object falls back to the ground.

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

Different Types of Gravity Batteries

Gravitricity Diagram showing wind energy stored using weights running in a shaft
Gravitricity

The most common example of a gravity battery today is also one in widespread use already. Power companies pump water into elevated reservoirs to store energy. Later, when they want to access that energy, the water is released and flows into another reservoir, 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 really scale down in a useful way.

There are companies such as Gravitricity that are building large gravity batteries that can be set up anywhere, unlike water reservoir solutions. Their demonstration rig uses two 25-tonne weights in a 15-meter (49.21ft) rig to supply 250KW of power. The company claims its technology can scale up to 20MW and that its systems have a 50-year design life.

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

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

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

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