Peak energy this summer could cost as much as 10 times the price Ruston is now charging, about 8 cents per kilowatt hour. The new merchant plants come in two varieties, both with gas turbine engines as the primary motive force. A simple cycle unit is a gas turbine engine driving a generator. While more fuel efficient than a conventional steam turbine, the gas turbine engine has a much higher maintenance cost and shorter life expectancy. The more complex combined cycle plant can start as quickly, but the hot turbine exhaust gases pass through a heat exchanger to create steam that drives a generator.
More energy is extracted from the same fuel.
Enough waste heat can be recovered from a 100 megawatt gas turbine to run a 25-30mw steam turbine. The fuel-efficient combined cycle generator can compete with other types of generators for more hours per year, typically about 5,000. The difference between the two systems is the demand for water during operation. Also like jet planes, both inject water into the airflow going to the engine. The water adds weight to the combustion gases passing through the hot end of the engine, generating more horsepower.