Storing Energy with Concrete Blocks

One of the big problems with alternative energy sources, such as wind and solar, is that they can’t generate electricity all the time. That means that that they need a way to store the excess energy they generate when they’re operating for times when they aren’t. The obvious answer—to most of us nerds—is to use batteries. The problem is that that solution doesn’t scale very well. In fact, 96% of energy storage is by “pumped hydro” where the excess energy is used to pump water up to a dam where it is stored until energy is needed. Then the dam is opened and the water flows against turbines to regenerate the electricity.

That solution also has problems, though. In the first place it requires the right geographic environment. Secondly, in some places water is too valuable a resource for this use. That’s why 75% of pumped hydro facilities have been built in just 10 countries. Still, the idea is a good one: store the energy as potential energy.

A startup named Energy Vault is leveraging the idea by storing energy by using cranes to lift concrete blocks and recovering the energy by letting gravity lower the blocks against the cranes’ motor to regenerate the electricity. Surprisingly, the system is almost as efficient as lithium-ion batteries.

Quartz has a nice article on the system. Energy Vault has built a demonstration plant—about one tenth the size of a production plant—to demonstrate the system. The concrete blocks for a production plant would weigh about 35 tons but the demonstration plant, which was built in 9 months and cost only $2 million, used blocks weighing 500 kg. A production plant could store about 20 megawatt-hours, enough to power to 2,000 Swiss homes for a day.

I love this solution. It’s low-tech in a way but about as efficient as more glamorous high-tech solutions. Read the article. It’s really interesting and illustrates how even simple ideas can yield huge benefits.

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