Unlike oil, which can be stored in tanks, and natural gas, which can be kept in underground caverns, electricity has been a challenge to bottle.
But that is starting to change.
These days, companies including Elon Musk’s Tesla Inc. are selling lithium-ion batteries, similar to those that power electric cars, to utilities, businesses and homeowners, who use them to store electricity, mostly for short periods.
But now, some nonbattery technologies are gaining traction as utilities continue to look for economical ways to capture and store power.
These alternatives have a longer lifetime than chemical batteries, which generally need to be switched out after about 10 years, and some can store and discharge more electricity.
Here’s a look at three of the technologies.
PUMPED HYDROPOWER: Pumped hydropower is a century-old technology that is getting a fresh look, as developers turn old mines into holding tanks for water. During periods when electricity is cheap and abundant, pumps are used to push large volumes of water uphill, where it is stored in giant basins. When extra power is needed on the grid, the water is released and gravity pulls it downhill and through generators that produce electricity.
Eagle Crest Energy Co. plans to build a $2 billion pumped-hydropower facility at an abandoned iron mine east of Palm Springs, Calif. The plant would have a capacity of 1,300 megawatts, enough to power nearly one million homes, and would be able to generate power for about 10 hours at a time. The plant could soak up excess power overnight, when demand is slack, and during the day, when California’s solar farms are churning out electricity, and then return the juice in the evening, after the sun sets and power use rises in cities and towns. Several similar projects are awaiting government permits.
FLYWHEELS: Flywheels store electricity in the form of kinetic energy. The basic technology, in which a wheel spins at high speed, has been around for decades and used for various applications, including storing and discharging power in momentary spurts. Newer flywheels, such as those developed by Amber Kinetics Inc., based in Union City, Calif., can hold their rotation longer, creating electricity that can be discharged over four hours.
With Amber Kinetics’ technology, an electric motor turns a 5,000-pound steel rotor until it is spinning at thousands of rotations a minute, a process that takes a few hours. The rotor is housed inside a vacuum chamber—the air is sucked out to remove friction. An electromagnet overhead lifts the steel rotor off its bearings, which allows it to spin quickly without requiring a lot of electricity. Indeed, the company says the steel disks, which resemble giant hockey pucks, can maintain their rotation with the same amount of electricity as it takes to power a 75-watt lightbulb.
The flywheel stores the energy in its continuous motion. When power is needed on the grid, the flywheel connects to a generator, and its momentum turns the generator’s shaft to produce electricity.
COMPRESSED AIR: Machines that use compressed air have been around for more than 100 years. Various attempts to use compressed air to store electricity have been tried over the past few decades, but high costs and technical challenges kept the technology from advancing, until now, according to Toronto-based Hydrostor, which is building next-generation compressed-air energy-storage facilities in Canada and Aruba, and says it is in talks with two utilities for additional projects.
Hydrostor uses electricity when it is cheap and abundant to run an air compressor, purchased off the shelf from General Electric Co. or Siemens. The compressor squeezes air into a pipeline and down into a hole the length and width of a football field and up to four stories tall, that the company digs deep underground and fills with water. When the pressurized air is piped into the underground cavern, it displace the water up a shaft and into an adjacent pond. Then the pipeline valve is shut. When electricity is needed, the valve of the air pipe is opened and the air rushes up.
When air is compressed, it becomes hot. To be stored, the air needs to be cooled, but to be reused to generate electricity, it needs to be hot. In the old days, the heat from the compressed air would be vented, and later the air would be reheated using a natural-gas-fired motor. Hydrostor, however, removes the heat from the compressed air and stores it in a tank filled with waxes and salts. When the air is brought back up to the surface, it is reheated with the hot wax and salts, then pushed through a turbine, where it generates electricity.
Ms. Sweet is a writer in San Francisco. She can be reached at firstname.lastname@example.org.
Appeared in the May. 22, 2017, print edition as ‘Beyond Batteries.’