AROUND THE WORLD AT SOLAR POWER PLANTS

A Potential Breakthrough In Harnessing the Sun’s Energy
David Biello, 27 April 2009 (Yale Environment 360)

SUMMARY
The enormous rising international enthusiasm for solar power plant technology is not about megawatts. It’s about hours, hours when there is no sun. Solar power plant technology offers a way to store solar energy and use it "when the sun don't shine."

In pursuit of the elusive dispatchable New Energy, entrepreneurs are taking a solar power plant concept born in the Negev Desert of Israel and developed in the Mojave Desert of California and building it in places like Spain, Algeria and Australia.

There are, broadly speaking, 2 types of proven solar power plants. They operate at temperatures approaching 1,000 degrees Fahrenheit. One has pipes running through a system of parabolic mirrors. The mirrors concentrate the sun’s heat on the substance in the pipes (in the past it was water or oil). The substance flows to a central plant where the heat boils water (in the same way that coal, natural gas and nuclear energy are used to boil water). The resultant steam drives a turbine in the same way that steam drives turbines at other power plants. In the other type of solar power plant, a field of mirrors focuses the sun’s heat on a central spot (usually the top of a “power tower”) where a substance is heated and flows to boil water to make steam to drive a turbine.

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There is a 3RD solar power plant technology that incorporates something called a Stirling engine. Although still unproven except under experimental conditions, it essentially combines elements of the 2 proven technologies.

The newest breakthrough: The substance in the pipes that flows to heat water to create steam is no longer water or oil but molten salts, sodium and potassium nitrates that hold the heat exceptionally well. They flow through the 2 solar power plant technologies in the same way as the water and oil, and do the same work, but after the sun stops heating them they can be stored for a few hours. One plant can store 28,000 metric tons of the salts. After the sun goes down, the salts continue to boil water, make steam and drive the turbines to generate electricity.

Engineers believe the potential exists for the salts to hold enough heat to drive the turbine all through a night, meaning a solar power plant could function around the clock. After the salts lose their heat, they are stored for use again the next day.

In some power plant systems, the substance that flows in the pipes is still water or oil. The molten salts are heated by excess capacity and used to keep the flowing liquid hot enough to drive the turbines after the sun’s heat has diminished.

Abengoa Solar and Arizona Public Services are using the molten salts technology at the Solana power plant southwest of Phoenix, Arizona.

At the Andasol project in the high desert of southern Spain, near Granada, an array of parabolic mirrors heats oil to 750 degrees Fahrenheit. Excess capacity heats vats of molten salts. The 50-megawatt Andasol 1 installation began operating in November 2008. Andasol 2 will come online in summer 2009. Andasol 3 is under construction. The entire 150+ megawatt complex will be complete in 2011 and serve 150,000 homes.

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Ausra, a company that originated in Australia and now works in California, uses a compact linear Fresnel reflector (CLFR) technology that is yet another combination of the 2 basic concepts. Flat mirrors boil water in pipes. Storage is not of salts but of pressurized boiling water. Ausra claims to have adequate storage capability for 24/7 generation. It brought a 5-megawatt demonstration plant online near Bakersfield, California, in 2008, and is planning a 177-megawatt plant in the same region as well as a 75-megawatt project with Florida utility FP&L near Miami.

Because solar energy is strongest and most reliable during the heat of the afternoon when demand on traditional source power plants peaks, solar power plants are also being built on coal and natural gas plant sites for peak demand smoothing.

Solar power plants used in this way reduce the greenhouse gas emissions (GhGs) of fossil fuel plants significantly beyond the number of megawatts they contribute because when fossil fuel plants do not need to ramp up to meet peak demand they can generate at a more even rate and far less energy is wasted. Such combined projects are under development at gas plants in Algeria and Egypt and will be studied in the U.S. states of Arizona, New Mexico, Nevada, and North Carolina.

Ausra’s first installation, in Australia, added a crucial 9 megawatts to a giant 2,000-megawatt coal station. Ausra is also making plans to provide steam generation to oil fields that use the steam to enhance their production. Ausra says the oil will be brought up and used anyway so why not do so with GhG-free solar-generated steam?

Abengoa Solar is building an 11-megawatt solar power tower outside Seville, Spain. The 64-megawatt Nevada Solar One, built by Spain’s Acciona Solar, uses parablolic trough mirrors made by Germany’s Flabeg AG. BrightSource Energy is planning 1,300 megawatts of solar power tower projects for Southern California Edison in the California deserts.

3,100 megawatts of solar power plant capacity are expected to be in place in the U.S. by 2012 and world capacity is expected to reach 6,400 megawatts in the same time frame.

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COMMENTARY
Research from the German Aerospace Center: 16,000 square kilometers of solar power plants in North Africa could — IF there is a high-voltage, direct-current transmission infrastructure to carry it — generate enough electricity for all of Europe.

Al Gore: Enough sun falls on the land masses of the earth in 45 minutes to power the world for a year.

Conventional wisdom: Solar power plants on 1% of the earth’s desert surface (about the size of Austria) could power the entire world.

Andasol. (click to enlarge)

History: The contemporary solar power plant concept emerged during the “false renaissance” of the 1970s when tension in the Middle East drove oil prices fronm $3/barrel to $12/barrel and sparked a New Energy boom. Israeli and U.S. engineer-entrepreneurs built the Solar Energy Generating Systems (SEGS) power plant in the California’s Mojave Desert in 1984, using the parabolic mirror design. They speculated about storage but did not build it. The Reagan administration phased out spending on New Energy R&D and withdrew the drive sparked by the Carter administration and the oil crises. The drop in oil and natural gas prices in the late 1980s and 1990s ended interest in improving or expanding SEGS.

Until now.

Economics: An average 6 kilowatt-hours of solar energy per square meter hits the earth’s surface daily. Solar power plant technology is the cheapest way to harvest it. Photovoltaic (PV) panels convert sunlight to electricity at (estimates vary) ~40 cents per kilowatt-hour. Proven solar power plant technology converts the sun’s heat to mechanical energy that generates electricity at ~13 cents per kilowatt-hour. The average 2008 U.S. coal-generated electricity price was ~11 cents per kilowatt-hour. (These are reported figures from the National Renewable Energy Laboratory, NREL, of the U.S. Department of Energy, DOE. Price estimates vary widely.)

What does not vary: In a carbon-constrained world forced to deal with global climate change, the cost of burning coal to make electricity will go up. As nascent solar power plant technology develops momentum, prices will come down.

Speaking of nascent technology, the unique design of Stirling Engine Systems is moving ever-nearer a challenging real-world trial in the deserts outside San Diego, California.

There has been tension between solar power plant developers and environmentalists over land use and potential harms to wildlife, habitat and landscape. Ongoing, relatively amicable efforts to reach compromise and assent have been relatively successful. One thing both sides agree on: Without New Energy, climate change will do far worse harm than individual installations. Particular places may be compromised on behalf of this good earth. (See DOING THE RIGHT THING THE RIGHT WAY, NEW ENERGY’S BIGGEST CHALLENGE)

Schematic of the storage system at Andasol. (click to enlarge)

QUOTES
- Sven Moormann, spokesman, Andasol builder Solar Millennium: “The turbine is running more hours every day because we have storage and we have the possibility to plan our electricity production…”
- Barbara Lockwood, renewable energy manager, Arizona Public Services: “One of the great things about molten salt technology is that you can get more energy out of the same facility…”

From beyondzeroemissions via YouTube.

- Terry Murphy, President/CEO, SolarReserve “We’re not going to solve the [climate change] problem without putting large-scale concentrated solar facilities in the American Southwest…It doesn’t take that big a footprint to make a pretty big impact…People need to look at this as a hedge against fossil fuel prices…You could start deploying a new type of power plant. We used to burn coal and natural gas — now we can use the sun to make steam.”