Compressed Air Energy Storage is already used in a few locations. Excess energy is used to pump air into underground caverns. When power is needed, the air is released, powering turbines. This is similar to pumped hydro, one of the oldest methods of stored energy. Water is pumped uphill into holding areas then released when needed to create energy. Thin Red Line says using underwater sacs to store compressed air might be more efficient than on land.
“For UW-CAES [at depths of 400 to 700 meters], the pressure remains almost constant for all levels of fill,” said Seamus Garvey, a professor of dynamics at the University of Nottingham in the U.K. “In effect, this means that for a given upper pressure, each cubic meter of air storage delivers about three times as much energy storage.”
“If you pump air into a cavern, you have a fixed volume. So the more air you let out of a limestone cave with compressed air, the more the pressure is going to drop,” said De Jong. “But with UW-CAES, the ocean [pressure] is always pushing on the bag.”
Toronto will be installing UW-CAES in Lake Ontario to supplement power on days where usage is 20% above normal. Intially it will be 750 KW, expanding to 2 MW.