GE wants to package eSolar’s solar-thermal technology, which uses a large field of mirrors to focus the sun on a central tower to produce steam, with a new line of natural-gas plants known to as "combined cycle" systems because they capture their own waste heat to power a steam cycle. This process increases the plant’s operating efficiency. The combined-cycle plants achieve up to 61 percent efficiency and use a new type of gas turbine that can more quickly adapt to the variability of some renewable energy sources, such as solar.
Adding eSolar’s technology could boost that efficiency even further. Its precisely positioned mirrors achieve temperatures of up to 580 °C and produce enough heat to turn water into steam. When the sun is shining, the steam augments the steam cycle of GE’s natural-gas plant, increasing overall plant efficiency to around 70 percent.
Such hybrid facilities, called integrated solar combined-cycle plants, are considered one of the most economical ways to introduce solar energy to a country’s power mix. This is especially true in Africa, the Middle East, and the sunnier parts of Europe and the United States, where GE and eSolar plan to focus their sales efforts.
Integrating solar-thermal technology with gas plants means they can share the same steam turbines, generators, and switch gear, potentially cutting the cost of solar thermal in half, according to Justin Zachary, a solar thermal expert with Bechtel. "This is a natural fit," says Zachary. But he says there is still plenty to learn. "It will take some time to prove the current technologies," he says. "The integration of the two systems in terms of controls and water quality still represents serious challenges."
Areva and Alstom, both of France, and Germany’s Siemens have made similar investments over the past two years, and each have a hybrid concentrated solar-gas plant offering. There are several integrated solar-gas plants under construction in North Africa and the Middle East. GE’s first concentrated solar energy project is a 530-megawatt plant in Turkey that will include 50 megawatts of eSolar’s solar thermal technology. The project, expected to be operational in 2015, will also integrate 22 megawatts of wind energy.www.technologyreview.com/