Jethro Mullen for CNN:  Fed up with their hefty electricity bill, managers at Cochin International Airport in southern India took matters into their own hands.

Three years ago, they began adding solar panels -- first on the roof of the arrivals terminal, then on and around an aircraft hangar. The success of those initial efforts led to a much bigger endeavor.

"We wanted to be independent of the electricity utility grid," Jose Thomas, the airport's general manager, told CNNMoney.

Last year, the airport commissioned the German company Bosch to build a vast 45-acre solar plant on unused land near the international cargo terminal.

The plant came online in August, making Cochin the world's first fully solar-powered airport.

The tens of thousands of panels generate on average slightly more than the roughly 48,000-50,000 kilowatts of power that the airport -- the seventh busiest in India -- uses per day, according to Thomas. Surplus energy is fed into the wider electricity grid.

The big project cost around 620 million rupees ($9.3 million), a sum the airport expects to save in less than six years by not having to pay electricity bills anymore. It also estimates the solar plant will avoid more than 300,000 metric tons of carbon emissions from coal power over the next 25 years.  Cont'd...