While utilities across the country are plugging in solar and wind, they also are in various stages of installing intelligent grid systems to improve control, conservation and reliability. Critical to these efforts is building bulk and distributed storage capacity.
“We have seen a dramatic increase in the participation by utilities in our energy storage research program,” said Dan Rastler, man-ager of the energy storage program at the Electric Power Research Institute (EPRI). “Energy storage is a key asset in the smart grid, espe-cially when it comes to wind power intermittency.”
Two of the most promising storage technologies are pumped hydro and compressed air energy storage (CAES).
Pumped hydro is the largest storage method currently being used in the United States. Water is pumped from a lower elevation to a higher elevation using lower-cost, off-peak power. During peak demand, the water is released to drive turbines.
Besides offering backup power, it helps utilities balance loads and sell more electricity when prices are highest. In February 2009, U.S. Energy Secretary Steven Chu said, “Pumped storage is perfect for renewable energy.” Now, it is ideal when you have excess wind generation at night and demand is low, but there are many areas in the country that do not have the water supply or the elevated reser-voirs needed to store it.
In May, the governors of Oregon, Idaho, Montana and Washington sent a letter to Chu voicing support for studying pumped storage in their states. The governors are not advocating construction of new dams but are rather encouraging diverting water into storage ponds from where water could be sent downhill through turbines when electricity is needed.
As for CAES, there are only two plants in the world: a 290-megawatt (MW) plant in Huntorf, Germany, built in 1978, and a 110-MW plant in McIntosh, Ala., that was commissioned in 1991. These first-generation plants have proved successful. CAES uses off-peak power to compress air and store it underground caverns, such as salt domes, aquifers or depleted natural gas wells. Storage pressures range from 800 to 2,000 pounds per square inch. During peak demand, compressed air is recovered and expanded to supplement power for standard combustion turbines.
“EPRI is working with over a dozen utilities to evaluate sites, technology and applications, and we are moving forward to build a large second-generation demonstration plant on the order of several hundreds of megawatts that could supply power for eight to 10 hours,” Rastler said.
For storage at the substation level, new flow-type and electrochemical battery systems are being deployed. Last year, American Elec-tric Power became the first U.S. utility to use advanced battery technology. It spent $27 million to buy six 1 MW sodium-sulfur batter-ies, each the size of a double-decker bus. Other utilities are considering battery systems housed in 40-foot trailers that can be moved where needed.
As we know, electricity is fleeting—use it or lose it. Now the buzzwords are “store it.”