Solar Thermal Power Coming to a Boil

Image Gallery A recent study indicates that over 90 percent of fossil fuel generated electricity in the United States and the majority of U.S. oil usage for transportation could be eliminated using solar thermal power plants — and for less than it would cost to continue importing oil. GERI KODEY/NREL

After emerging in 2006 from 15 years of hibernation, the solar thermal power industry experienced a surge in 2007, with 100 megawatts of new capacity coming online worldwide. During the 1990s, cheap fossil fuels, combined with a loss of state and federal incentives, put a damper on solar thermal power development. However, recent increases in energy prices, escalating concerns about global climate change, and fresh economic incentives are renewing interest in this technology.

Considering that the energy in sunlight reaching the earth in just 70 minutes is equivalent to annual global energy consumption, the potential for solar power is virtually unlimited. With concentrating solar thermal power (CSP) capacity expected to double every 16 months over the next five years, worldwide installed CSP capacity will reach 6,400 megawatts in 2012 — 14 times the current capacity. (Click here to see the history of concentrated solar thermal power capacity since 1980.)

Unlike solar photovoltaics, which use semiconductors to convert sunlight directly into electricity, concentrated solar thermal plants generate electricity using heat. Much like a magnifying glass, reflectors focus sunlight onto a fluid-filled vessel. The heat absorbed by the fluid is used to generate steam that drives a turbine to produce electricity. Power generation after sunset is possible by storing excess heat in large, insulated tanks filled with molten salt. Since CSP plants require high levels of direct solar radiation to operate efficiently, deserts make ideal locations. [Click here to read a New York Times article about the potential of concentrated solar power.]

Two big advantages of solar thermal plants over conventional power plants are that the electricity generation is clean and carbon-free and, since the sun is the energy source, there are no fuel costs. Energy storage in the form of heat is also significantly cheaper than battery storage of electricity, providing CSP with an economical means to overcome intermittency and deliver dispatchable power.

The United States and Spain are leading the world in the development of solar thermal power, with a combined total of over 5,600 megawatts of new capacity expected to come online by 2012. Representing over 90 percent of the projected new capacity by 2012, the output from these plants would be enough to meet the electrical needs of more than 1.7 million homes.

The largest solar thermal power complex in operation today is the Solar Electricity Generating Station in the Mojave Desert in California. Coming online between 1985 and 1991, the 354-megawatt complex has been producing enough power for 100,000 homes for almost two decades. In June 2007, the 64-megawatt Nevada Solar One plant became the first multi-megawatt commercial CSP plant to come online in the United States in 16 years.