Todd Woody reports on licensing of the nation’s first large-scale solar thermal power plant in two decades. Licensing of the 250-megawatt Beacon Solar Energy Project comes after a two-and-a-half-year environmental review. The author is now hopeful that several other big solar farms will receive approval from the California Energy Commission in the next month.
The Beacon solar thermal electric power plant will use long rows of mirrored parabolic troughs, which focus sunlight on liquid-filled tubes to create steam that drives an electricity-generating turbine. While using water may have been a business decision for NextEra developers, there certainly are other options, e.g., indirect dry cooling (Heller system) or using a molten salt loop to collect heat from the sun.
“I hope this is the first of many more large-scale solar projects we will permit,” said Jeffrey D. Byron, a member of the California Energy Commission, at a hearing in Sacramento on Wednesday. “This is exactly the type of project we want to see.”
Developers and regulators have been racing to license solar power plants and begin construction before the end of the year, when federal incentives for such renewable energy projects expire. California’s three investor-owned utilities also face a deadline to obtain 20 percent of their electricity from renewable sources by the end of 2010.
Still, it has been long slog as solar power plants planned for the Mojave Desert have become bogged down in disputes over their impact on protected wildlife and scarce water supplies.
The 50 MW La Florida solar farm uses parabolic trough technology and a molten salt system for thermal storage. The new, Archimede solar thermal electric power plant in Italy does not use molten salt just for thermal storage. It uses a molten salt loop to collect heat from the sun.
In March 2008, NextEra Energy Resources filed an application to build the Beacon project on 2,012 acres of former farmland in California’s Kern County… Some rural residents immediately objected to the 521 million gallons of groundwater the project would consume annually in an arid region on the western edge of the Mojave Desert. After contentious negotiations with regulators, NextEra agreed to use recycled water that will be piped in from a neighboring community.
“It’s been a lengthy process, an almost embarrassingly long lengthy process,” said Scott Busa, NextEra’s Beacon project manager, at Wednesday’s hearing. “Hopefully, we’re going from a lengthy process to a timely process.”
However, an attorney for a union group that has been critical of Beacon told commissioners that obstacles still stand in the way of the power plant.
“Despite all the hard work that has been done, this project won’t get built anytime soon,” said Tanya Gulesserian, representing California Unions for Reliable Energy. She cited the absence of a deal to sell electricity from the Beacon power plant to a utility.
Mr. Busa responded that NextEra is in the final stages of negotiating a power purchase agreement.
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IEEE Spectrum provides an update on the project. Since there is an increasingly limited water supply in California, regulators have pushed developers to employ water conservation practices on new plant designs.
Photo: Solar Millenium
To “get the green light,” project developers redesigned the cooling technology of the solar thermoelectric power plant. The change should reduce plant efficiency by 5 to 10 percent. “According to Solar Millennium, which is jointly developing the project with Ferrostaal and Chevron,” there also is an increase in the cost.
Solar-thermal plants like the ones planned at Blythe use trough-shaped mirrors to warm a heat-transfer fluid pumped through a pipe at the mirrors’ focal point. The hot fluid makes steam to turn a turbine and generate electricity. The steam must be cooled and condensed to complete the cycle. And in most solar-thermal plants, such as Solar Millennium’s massive Andasol plants in Spain, that requires a cooling tower that carries the heat away by evaporating water. On average, a typical 300-megawatt steam-cycle generator with cooling towers loses some 11 million liters of water a day to evaporation.
However, plants can use dry cooling—essentially a gigantic radiator—instead. "Because we are cooling the steam cycle of the turbines with air instead of water, we require 90 percent less water," says Josef Eichhammer, president of Solar Trust of America, the Solar Millennium-Ferrostaal joint venture.
However, dry cooling is less efficient than wet cooling, especially in summer. The turbine’s efficiency is related to the temperature difference between the hot steam and the cooled condensate. Lowering the temperature of the cooled side increases the pressure difference across the turbine, improving efficiency. Because wet cooling relies on evaporation, it can drive down the water temperature to below the temperature of the air outside the plant. Dry cooling can’t.
Blythe, where the plants will be located, is in California’s southeastern desert, just a stone’s throw from the Colorado River. But waters from the lower Colorado are already in high demand, with farmers, cities, and energy producers competing for it. And the area’s groundwater sources are limited. The Blythe plants were originally supposed to be wet cooled, but Solar Millennium changed the design because "the California Energy Commission prefers dry-cooled generation," says Rachel McMahon, director of government affairs for Solar Millennium.
The commission’s report on the project described air cooling’s efficiency in the Blythe environment as "poor," but it said that it was "a reasonable trade-off as it would prevent potentially significant environmental impacts that could result from consumption of the large quantities of water required by wet cooling."
According to the report, the entire project will use 740 megaliters of water per year for things such as washing the mirrors (283 ML) and supplying a fire suppression system. So the plant will provide its estimated 2200 gigawatt-hours of electricity for a miserly 363 liters per megawatt-hour. The water will come from wells to be drilled on-site.
New renewables projects, like Blythe, are critical to California, because state law mandates that 20 percent of utilities’ electricity be renewable in 2010. By 2020 it must be 33 percent.
The California Energy Commission is rushing to complete its review of a raft of solar projects before an offer for federal grants and loan guarantees expires at the end of the year. Last month, the commission approved the Beacon Solar Energy Project at the western edge of California’s Mojave Desert. Despite the desert environment the 250-MW plant is a allowed to consume 1.7 billion liters per year in a wet cooling system, because it will use treated municipal wastewater from nearby California City.
The next hurdle for the Blythe plants is U.S. Bureau of Land Management approval, which Solar Millennium expects to happen in October. The company plans to start construction of the first two of the four plants in 2010 and should have them connected to the grid in 2013 and 2014.
The Beacon Solar Energy Project is an example of how meeting the growing demand for energy, even through sustainable means, could entail greater threats to the environment. Circle of Blue, a network of journalists and scientists dedicated to water sustainability, warns that water scarcity in the U.S. and elsewhere in the world, is a problem too long ignored for the sake of progress.
While the Beacon Solar Energy Project continues to run the gauntlet, another project has faltered. “Tessera Solar North America, the developmental unit of Stirling Energy Systems Inc., has ended plans to jointly construct a 250 MW solar power plant with the city of Phoenix.”
Even though the City of Phoenix project has faltered, Tessera Solar is proceeding with construction of a project for BLM (Bureau of Land Management). Tom Kenworthy reports that The Department of Interior has approved two large solar energy projects on government land in southern California. Total capacity will amount to 754 megawatts.
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