Power plant built at John Wayne Airport

"This unassuming building will serve a purpose far greater than its simple exterior suggests," said Alan Murphy, airport director, at a dedication ceremony.

That purpose is "a stable, reliable, environmentally responsible source of power to support the airport and to reduce our demand on the electric grid," said Jenny Wedge, JWA spokeswoman.

About 95 percent of the airport's energy needs will be satisfied by the plant's natural-gas-fired engines, although Southern California Edison remains capable of fully powering Orange County's aviation hub.

Officials previously said the $31 million project would pay for itself within a decade, but have backed off that assertion. While $1.7 million annually at today's rates will be saved by not buying electricity from the grid, that will be offset by operating costs, such as hiring a contractor to run the plant and buying natural gas.