The U.S. Energy Information Administration reported that 17 percent of all electricity produced in the United States in 2017 came from renewable energy sources, including solar, wind and hydroelectric dams. That percentage is expected to keep growing as communities seek ways to improve local air quality and reduce greenhouse gas emissions linked by EPA scientists to climate change.
Unfortunately, renewable energy sources need proper weather conditions to generate power. And those periods of sunshine, wind or heavy wave action occur only intermittently between 4 p.m. and 9 p.m. when consumer demand for electricity peaks.
That’s where energy storage technology comes in.
The Importance of Energy Storage Technology
“If we have energy storage on the grid, we can store excess renewable energy during the day, then distribute it at 6 p.m. when people are getting home from work, turning on their TVs and air conditioners,” explained Wes Jones, a spokesperson for San Diego Gas & Electric (SDG&E).
This technology, he added, is also critical for maintaining the stability and reliability of the nation’s power grid, which nominally delivers electricity to our outlets at 60 cycles per second (Hz). Grid conditions can cause this frequency to fluctuate. Grid operators can use energy storage assets to add or remove power from the grid to help stabilize the frequency.
Pumping for Power
The Department of Energy identified pumped hydroelectric energy storage (PHES) as the most dominant energy storage technology in use today. This technology creates power by pumping water to higher elevations when electricity is plentiful. During peak demand periods, the water is released and allowed to run through turbines that generate electricity. The 1682 MW pumped hydro Castaic Power Plant operated by the Los Angeles Department of Water and Power, for example, accounts for 2.5 percent of the utility’s power portfolio and serves approximately 73,000 customers, according to Louis Ting, LADWP’s director of power plant development and engineering.
A related technology is called compressed air energy storage (CAES). “Think of [CAES] like ‘pumped aero,'” said Ting. “Instead of pumping water from one elevation to another, CAES uses excess renewable energy to compress air and pump it under pressure into underground caverns. When demand is high, the air is heated, released and used to drive turbines that generate electricity.”
In Lithium-Ion We Trust
Lithium-ion batteries, the same technology used in your laptop or smartphone, are one of the most pervasive forms of energy storage technology in use today, according to Laurence Abcede, SDG&E’s manager for distributed energy systems.
“Lithium-ion technology is appropriate for both stationary and mobile batteries,” he said. “It is cost effective, very reliable and modular, which means you can use it in nearly any application.” The New York Times coverage, however, suggested that fire safety concerns with the technology remain.
Nonetheless, lithium-ion remains the primary energy storage technology for many new battery storage facilities being developed in California, according to SDG&E news materials.
Next in Line
IEEE Spectrum magazine highlighted another promising energy storage technology for the grid known as the vanadium redox flow battery. Developed in the mid-1980s at the University of South Wales in Sydney, Australia, VRF technology was matured in 2011 by a team at the DoE’s Pacific Northwest National Laboratory in Washington State.
Unlike lithium batteries, which store energy in small cells, VRF batteries store their energy in two tanks of electrolytes separated by an ion exchange membrane. The battery generates a current by converting the chemical energy of the electrolytes into electrical energy; reversing this process allows the battery to charge itself from the electric grid. The requirement to maintain two tanks of electrolytes and related pumping equipment makes VRF technology better suited to utility-scale applications than portable applications.
Durable Design, Longer Life
VRF batteries also offer compelling performance benefits over lithium ion.
“VRF batteries have a lifespan of 20+ years and can be completely charged and discharged repeatedly, without damaging the battery system,” explained Abcede. “Best of all,” he added, “VRF technology is not combustible.”
The DoE reported that VRF technology is being used widely today in Asia and Europe, with a growing presence in the U.S.
A Multi-Purpose Future
Jeff Bishop, CEO for Key Capture Energy, a Houston-based developer of grid-scale electric projects, views energy storage as “the Swiss Army knife of the electric industry,” serving the grid in many new and unexpected ways.
“You’re going to see storage paired with solar and wind power generation facilities both on- and offshore, and used increasingly as central generation to replace fossil fuels,” he said. “It will also help reduce the need for new transmission infrastructure, serve as a microgrid for installations such as hospitals, and add reliability and stability to the electric grid.”
“As costs come down and the technology matures, it’s going to be unstoppable.”