These companies want to go beyond batteries to store energy

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If y'all have been around for a while, you know that I love writing about batteries (see exhibits A, B, and C). Using chemical reactions to store energy is handy and scaleable, and there are about a million ways to do it, which is why batteries have basically become synonymous with energy storage.

But more groups are starting to think outside the battery. In an effort to cut costs and store lots of energy for long periods of time, researchers and companies alike are getting creative: pumping water into the earth, compressing gas in underground caverns or massive tanks, even lifting giant blocks.

As we build more renewable energy capacity in the form of variable sources like wind and solar power, we're going to need to add a lot more energy storage to the grid to keep it stable and ensure there's a way to get electricity to the people who need it. Some of that energy storage might look a little different from the batteries we usually talk about around here, so let's take a closer look at why battery alternatives are popping up, and what it might take to make them a reality.

A certain gravitas

As you may remember from high school physics class, energy can be stored in the form of potential energy: lift up a book, and there's energy stored in it that's released when you let go and gravity pulls it down. (That falling is kinetic energy in action.)

This simple concept, in the form of pumped-storage hydropower, is the foundation of 90% of global grid storage today. That's right-the vast majority of the world's energy storage comes from moving water uphill.

In a pumped hydro plant, extra electricity is used to force water uphill from one reservoir to another. Later on, just open up the gates and let gravity do its thing: water flows downhill through a turbine, generating electricity. It's a cheap, relatively straightforward way to store energy for later.

It's tough to scale pumped hydro, though, since it requires specific geographic conditions (not to mention that disrupting natural water systems can be really destructive for ecosystems).

Some groups want to reimagine energy storage, harnessing gravity without relying on water. EnergyVault is building facilities with elevators that raise and lower gigantic bricks to store energy. Gravitricity wants to lift huge weights underground, maybe in old mine shafts.

These systems might have high efficiency, returning a lot of the energy that's put into them. They may also last a long time, so it could be economical to store energy for days, weeks, or maybe even months.

Proponents say gravity-based systems could help meet demand for long-duration storage. But there's also skepticism about the future of the approach, since they'll require a lot of work to build, and they might be tougher to maintain than expected. EnergyVault is making progress on a planned facility in China, though the company has also been deploying a lot of lithium-ion battery installations these days.

The big squeeze

Let's go back to high school physics one more time for another concept: pressure. If you squeeze something into a smaller space, you're raising the pressure.

Turning that pressure into usable energy is the idea behind compressed-air energy storage. All you need is an underground salt cavern. When you've got electricity you need to use, you can run pumps to push air inside the cavern. Then, when you need to get energy out, just release a valve and let the escaping air spin a turbine to generate electricity again.

There are only a couple of these facilities running worldwide, one in Germany and another in Alabama. In the past, they've been tied up with fossil fuels, since they usually work alongside natural-gas power plants. But now companies want to reimagine compressed-air storage, using it for renewables and expanding where it can be used.

Earlier this year, local governments in California signed contracts with Hydrostor, which is building what would be the world's largest compressed-air storage facility. Instead of relying on natural geological conditions, Hydrostor will drill three shafts deep into the earth to store the compressed air.

It's a billion-dollar project, and it could be operating as soon as 2028 to store energy and help smooth out California's grid using nothing but air.

Other groups want to take a different approach to the same concept. Energy Dome, an Italian startup, wants to compress carbon dioxide instead of air to store energy. This wouldn't require large underground storage caverns at all-for more on the details here, check out my story from last year on Energy Dome.

Earth to battery

Some groups are also looking to pair these new approaches to energy storage with efforts to generate electricity, making new power plants more flexible.

Take geothermal energy, which harnesses heat from inside the earth. Geothermal power plants are usually used for what's called baseload energy, running at about the same capacity all the time.

Now, though, a startup called Fervo Energy has shown that it can store energy using its geothermal wells. By pumping water into them, it can increase the pressure underground over time-and when that pressure is released, the geothermal plant produces more energy than usual.

It's a fascinating twist on energy storage and could transform what geothermal plants are capable of in the future. My colleague James Temple got to visit Fervo's test site and published a story about the startup's efforts earlier this week. Give it a read to get all the details.

BRYCE VICKMARKAnother thing

You might not be familiar with ARPA-E, but the government agency is helping shape the future of energy. Part of the DOE, ARPA-E supports high-risk, high-reward energy technologies. I sat down with its new director, Evelyn Wang, to talk about what technologies could transform energy in the future. Check out my story from Monday for more.

Keeping up with climate

The United Nations reached a major agreement to protect ocean biodiversity. If it's ratified, the treaty will create a group to govern the high seas. (New York Times)

Do you really need that bigger EV battery? Researchers followed around hundreds of drivers for a year in the US and found that nearly 40% of drivers could make ALL their trips in a small electric vehicle with just 143 miles of range. (Inside Climate News)

One of the new Plant Vogtle nuclear reactors in Georgia just reached self-sustaining nuclear fission. The project has been plagued by delays and cost increases. (Associated Press)

The way we eat is really rough on the climate-the food sector could cause nearly 1 C of warming by 2100. Addressing meat consumption and food waste could help. (The Verge)

Some companies want to use food waste for energy, which could help cut harmful greenhouse-gas emissions. (MIT Technology Review)

There's a divide in the US ... in how we heat our homes. It could have an impact on decarbonization, because replacing oil in Maine will present different challenges than replacing natural gas through the Midwest and Northeast. (Washington Post)

Construction began last week on a controversial lithium mine in Nevada. Environmental groups and Indigenous tribes in the area have opposed the project, arguing that the land has cultural and religious importance and the work could cause ecological harm. (Grist)

For the newsletter, I took a look at three myths about mining and renewable energy. (MIT Technology Review)