The U.S. Environmental Protection Agency’s (EPA’s) plan to regulate carbon emissions is just the latest challenge facing the U.S. electric power system. Technological innovation is disrupting old ways of doing business and accelerating grid modernization. Earlier this year, AEE released Advanced Energy Technologies for Greenhouse Gas Reduction, a report detailing the use, application, and benefits of 40 specific advanced energy technologies and services. This post is one in a series drawn from the technology profiles within that report.
Gas turbine technology is mature and in wide use. In its most basic configuration – the simple cycle gas turbine (SCGT) – air is compressed, mixed with fuel (most frequently natural-gas), and the mixture is burned in a combustor. The resulting hot, pressurized gases are expanded through a turbine that drives the compressor and an electric generator. SCGTs have conversion efficiencies of up to about 40%. In a combined cycle gas turbine (CCGT) plant, the hot exhaust gases leaving the turbine pass through a heat recovery steam generator, which produces high-pressure steam that drives a steam turbine connected to a generator, producing more electricity with no additional fuel input. This increases overall electrical efficiency to nearly 60%, making CCGTs the most efficient conventional power plants available.
Gas turbines come in a wide range of sizes and can be used to meet varying needs, from large baseload plants to small distributed and onsite generation installations. The availability of low- priced natural gas in the United States has driven up the utilization rates of existing SCGT and CCGT capacity. U.S. electricity generated from natural gas increased to 27% in 2013, compared to 18% in 2004. The increase in natural gas powered electricity generation played a role in reducing US carbon emissions close to 10% since 2005. More than half of new U.S. generation capacity in 2013 was comprised of natural gas turbine plants with investment and deployment expected to increase in the coming decade.
The capital cost of a CCGT plant is about $1,000/kW, significantly lower than other baseload options such as coal. When coupled with inexpensive natural gas, CCGT economics compare favorably to other new-build options. SCGTs and CCGTs have rapid startup and ramping capabilities that add flexibility to the grid and can support integration of variable renewable generation. As SCGT and CCGT plants mostly burn natural gas, they emit very low levels of criteria pollutants. Through a combination of higher efficiency and the use of a lower-carbon fuel, CCGT plants emit about half the CO2 of even the best (i.e., supercritical) modern coal plant.
