In this era of high concern for energy consumption, readily available energy-efficient motors top the 96% mark, electric drives reach 95%, and many appliances and consumer devices exhibit rising efficiency. What, then, makes 60% thermal efficiency so special?

It’s a much different scenario for power generation. Complex combustion and fluid-flow processes involved in power conversion limit thermal efficiency, despite application of the best engineering know-how. For example, a typical light-water reactor nuclear power plant offers thermal efficiency around 35%, while a modern coal-powered plant with super-critical boiler tops out at 44%.

However, one power technology, the gas turbine, has been pushing the efficiency envelope. These large, land-based (stationary) turbines—with 100s of megawatt (MW) output—draw on the advances in design, materials, and cooling techniques of their more numerous aircraft gas turbine cousins. The latest turbines offer thermal efficiencies in the 40% range, with a recent model reportedly obtaining 46%.

These values refer to simple-cycle operation, where turbine exhaust is not further used. Real advantage comes from gas turbine exhaust applied as input to a standard steam turbine in a combined-cycle power plant. This is where new-generation gas turbines can become the driving engine to obtain 60%+ overall thermal efficiency.

Among stationary gas turbine suppliers, developments from two manufacturers are particularly noteworthy. GE Energy installed the first of its H systems (combined-cycle gas and steam turbine) at Baglan Bay power station in South Wales (U.K.). The plant went commercial in 2003 and, to date, has logged over 30,000 operating hours. Currently it runs at 480 MW, with capability for higher output, according to GE Energy.

Five other GE H turbines are in various stages of implementation; three are in Japan at Tokyo Electric Power Co.’s (TEPCO’s) Futtsu thermal power station. The first of these 50-Hz machines was initially fired in Dec. 2007, and is expected to be in operation in late summer 2008. H systems in TEPCO Units 2 and 3 are scheduled to run by mid-2010.

GE’s first H-class turbine in the U.S., also its first 60-Hz machine, was installed in 2006 at Inland Empire Energy Center—a natural gas combined-cycle power plant in Riverside County, CA. Two GE H systems will comprise this plant, which is designed for maximum net rated electrical output of 775 MW to domestic and business users. Inland’s two units are scheduled to go online later this summer.

Meanwhile, Siemens Power Generation is moving its H-class SGT5-8000H turbine toward commercialization. Installed at the Irsching 4 gas power plant near Ingolstadt, Germany, the first firing of the turbine occurred in Dec. 2007. First synchronization to the grid followed in March 2008 and full-load testing (simple-cycle mode) started in April 2008, notes Phillip Ratliff, director of next-generation gas turbines at Siemens.

Siemens’ 50-Hz machine outputs 340 MW, but is designed to produce 530 MW in eventual combined-cycle operation—with expected efficiency of more than 60%. “A 60-Hz turbine is being developed after further verification of the first design,” says Ratliff.

An extensive test and validation program will continue for the SGT5-8000H turbine until mid-2009. Then, build-out of the combined-cycle plant begins in phase 2 of the program, with transfer to the plant operator, E.ON Kraftwerke GmbH, expected in mid-2011.

The next couple of years look exciting for the gas turbine power generation arena.

ONLINE extra

Also read: New, efficient industrial gas turbines coming. The story describes GE Energy and Siemens Power Generation technologies that weigh up to 440 metric tons.