Wind and solar power has become so cheap to install, and sometimes so abundant, that utilities don't know what to do with it. Sometimes they pay other power plant owners not to produce electricity.
In response, scientists and engineers are racing to find ways to cheaply store that electricity for later use, ultimately aiming to store renewable energy and make it available 24/7 at a price that would put coal and natural gas out of business.
Cache Energy is the latest startup to attempt this feat, and it's taking a slightly different approach than the others. Rather than using sand or custom bricks to store electricity as heat, Cache stores the electricity through chemical bonds in pellets made from limestone. Founder and CEO Armpit Dwivedi calls this approach “coal with no impact.”
“This is a low-cost solid state that can generate heat and use some of the same infrastructure that was built around fossil fuels,” he told TechCrunch.
Dwivedi said the pellets could be stored in piles or silos, moved on conveyor belts or transported by rail car. “If you keep them physically contained, literally wrapped in a tarp, that's enough to keep them charged almost indefinitely.”
Cache Energy pellets can be stored in simple containers without losing their charge. Image credit: Cache Energy
Cache has operated quietly until now: Dwivedi founded the company in 2021 while he was about to finish his PhD at the University of Illinois, and gave TechCrunch an exclusive look at its technology, which aims to replace the role of fossil fuels in providing heat to homes and industries.
The startup got started with calcium hydroxide, which is widely used in everything from papermaking and sewage treatment to salting and nixtamalization, the process that turns cornmeal into tortilla masa. Calcium hydroxide is a powdery substance by itself, which makes it unsuitable for Cache's process; the particles are too small and tend to blow away, so the company came up with a way to bind the powder together so it would hold up over time.
But the pellets couldn't be too big, or they would interfere with the next step in the process: the reaction that stores and releases energy. “We went through a lot of iterations on size,” Dwivedi says.
When Cache's pellets are heated, they release water vapor, leaving behind calcium oxide, or quicklime, which is the battery's “charged” state. To discharge, Cache passes the pellets through the same gravity-fed reactor, flooding it with water, reversing the reaction and generating heat. Dwivedi says the entire system is about 95% efficient.
Cache's pellets can produce heat up to 550 degrees, enough to power most industrial processes, as well as the heating and hot water needs of commercial and residential buildings. Dwivedi said one shipping container of Cache pellets would be enough to power several office buildings through the winter. The company is working on a new version that can produce heat up to 900 degrees, expanding the range of industries it can sell to.
The startup recently raised $8.5 million in seed funding and is aiming to raise Series A by the end of the year. Investors in the seed round include Climate Capital, Evergreen Climate Innovations, Grantham Foundation, Halliburton Labs, Muus Climate Partners, Unshackled Ventures and Voyager Ventures. The startup currently has one customer-owned pilot reactor, and Dwivedi said the upcoming funding will be used to ship more reactors to customers.
Cache's goal is to keep equipment and material costs as low as possible: The company uses as many off-the-shelf components as possible, and the pellets themselves cost only about 20 to 40 cents per kilowatt-hour, despite current production of about 500 kilowatt-hours per hour.
Cache's ability to compete with fossil fuels depends heavily on electricity prices. In places where wind and solar are plentiful, pellets are cheap to buy. As with any arbitrage opportunity, the key is to buy as cheaply as possible.
If Cache's pellets can withstand the rigors of real-world use, you can imagine them being charged in solar- and wind-rich areas like Texas and Arizona, then shipped across the country to help run industrial facilities or heat office buildings. “You could even store the pellets in your basement if you wanted,” Dwivedi says. Imagine Cache trucks delivering pellets every year before winter sets in, just like heating oil trucks still do in the Northeast. That could be a major contribution to decarbonizing heating, one of the last bastions of fossil fuels.