Houston startup plans to store wind energy underground 

Texans have long stored oil, natural gas and other forms of energy in underground salt caverns, so it’s only natural that a Houston startup wants to store wind energy there, too.

The method is in the company’s name, Apex-CAES, where CAES stands for compressed air energy storage. The company plans to use electricity at night, when it’s cheap, to compress air into an underground cavern. The company then releases the air through turbines to generate electricity when the price is right.

The only thing holding back this 30-year-old technology has been the economics. The difference between the high and low prices in a 24-hour period has not been large enough to generate a reasonable return on the capital investment.

Texas’ wholesale electricity market and huge nightly wind resource, though, make compressed air energy storage viable, said Jack Farley, CEO of Apex-CAES. Build enough compressed air energy storage, and Texas would never have to burn coal again, and consumers would enjoy even lower electricity prices, he told me.

“I think you could turn off all fossil-fuel generators in Texas when you wanted to,” he said.

Apex-CAES is raising $500 million to build its first facility near Palestine. Located near five existing natural gas storage caverns, the compressed air would spin turbines rated at 317 megawatts, capable of generating 15,000 megawatt-hours of electricity over two days without a recharge. The company, though, would never want to release all the air.

The big opportunity for energy storage companies, whether they use batteries, compressed air or hydroelectric dams, is to keep the electric grid balanced as people turn appliances on and off and while generators ramp up and shut down. Sources of electricity that keep the system smoothed out are called ancillary services, and they earn a premium from grid operators like ERCOT, the nonprofit grid manager that supplies electricity to most of Texas.

ERCOT also pays a premium for responsive reserves, electricity that is immediately available on a moment’s notice in case of an emergency. While compressed air energy can’t compete with low-priced natural gas or wind in the bulk electricity market, it can compete to offer reliable ancillary services.

Compressed air has both a price and operational advantage over batteries. Salt caverns are cheaper than lithium-ion batteries, and the system can fill the cavern with air while generating electricity. You can’t charge and discharge a battery at the same time.

Operators can easily and quickly adjust output to match the needs of the grid – unlike with a natural gas turbine. In many ways, compressed air storage operates like a hydroelectric dam.

“ERCOT uses a regulation product every second of every day. They deploy responsive reserves about eight times per month, every month of the year,” Farley said. “We would be there for the grid 24 hours a day, 365 days a year, to balance the system and keep it at 60 hertz.”

The secret sauce is Texas’ cheap wind power, which during the spring, fall and much of the winter is basically free at night because there is so much of it.

Texas has 19 gigawatts of installed wind turbine capacity and is expected to add another 10 gigawatts by 2020.

The only thing preventing Texas from building more wind, solar and compressed air energy storage is the low price of natural gas.

With prices averaging below $3 for a million BTUs, the electricity business is a tough place to make a profit right now.

Old attitudes are also a problem. Critics of clean energy complain about the intermittence of wind and solar power, and the high cost of lithium-ion batteries. Sure, solar is strongest during the day and wind produces the most at night, but the weather doesn’t always cooperate.

The renewable energy sector, though, is maturing, and because tax credits for it are rolling off by 2020, smart people are working to solve those problems.

Farley has identified suitable salt domes and caverns across most of the U.S. Wind and solar companies are building widely dispersed assets so that when weather is bad at one location, it’s probably good at another.

Americans are also waking up to the social benefits of converting to renewable energy and storage. Researchers at Carnegie Mellon University have calculated that shutting down coal plants and replacing them with natural gas has saved tens of thousands of lives. Getting rid of coal altogether would save tens of thousands more.

Apex will need a small amount of natural gas to heat the air it compresses to maximize turbine output. But storage facilities could limit natural gas usage to when demand peaks in the summer and winter while eliminating the need for coal completely.

The power sector is undergoing a revolution, and Americans should embrace and encourage startups like Apex-CAES. Just as innovators found a way to produce natural gas from shale rock and produce huge amounts of oil and natural gas, equally inventive innovators are working to solve the problems around clean energy. They are showing results.