Genesis Solar Goes Dry

By Published On: July 16, 2010

In a breakthrough agreement for licensing a major solar thermal power plant, NextEra Energy Resources plans to install a dry cooling system on its proposed 250 MW Genesis Solar Energy Project. The move reduces the water consumption impact in the California desert. The method could bump the cost of power from the plant by up to 10 percent and cut power output by up to 18 percent on hot days. NextEra negotiated the deal with the California Energy Commission staff in the middle of a July 12-13 evidentiary hearing in the licensing proceeding for the plant. NextEra plans to build the facility about 25 miles west of Blythe. “California projects are setting the global standard for best practices in solar thermal development,” stated V. John White, Center for Energy Efficiency and Renewable Technologies executive director, in response to the company’s decision. NextEra’s agreement to shift to dry cooling marks a significant concession, according to testimony the company filed with the Energy Commission May 18. Dry cooling saves water, the company noted, but it reduces the amount of energy produced for the grid. The Energy Commission favors dry cooling for new power plants in California to conserve on the state’s tight water supply. The state Water Resources Control Board in May voted to close 19 of California’s water-cooled power plants over the next decade indicating a clear policy away from using water to cool down turbines that heat up as a matter of course in electricity production. In the case of Genesis, the Energy Commission staff is concerned NextEra’s plan to pump groundwater to cool the steam turbines ultimately would cut the inflow to the over-used Colorado River, which lies downhill from the project site. “We’d like to see no net changes to that water body,” said Energy Commission staff counsel Caryn Holmes. The move from wet cooling to dry cooling should reduce the facility’s water use impact enough to make it less than significant under the California Environmental Quality Act, according to Holmes. As originally planned, the project would have used about 1,605 acre feet of water pumped from the Chuckwalla Valley groundwater basin each year, according to Energy Commission documents. Dry cooling should cut the annual water use to no more than 202 acre feet, almost a 90 percent reduction, said Scott Galati, the company’s attorney in the proceeding. Water use was one of the major unmitigated impacts the Energy Commission staff identified in analyzing the project. The others were its impact on landscape views and land-use. Company engineers told the Energy Commission dry cooling diminishes the efficiency of steam turbines, plus uses power to run giant cooling fans. Dry cooling systems also cost more to build than wet cooling systems, they added. Unlike running cold water around pipes containing hot steam for cooling, dry cooling systems operate in a closed loop like a car radiator. The steam and hot condensed water from the turbines circulates through a series of tubes over which fans blow cooler air. The cooled water then returns to the steam generator where it’s heated and runs through the turbines again in a continuous loop. NextEra engineers noted dry cooling systems are particularly inefficient in the desert when the weather is hot. To make up for the power losses, NextEra spokesperson Steve Stengel said the company plans to build more solar energy collection loops into the plant without enlarging its 1,800-acre footprint. That will cost more, he said, but the company still is trying to figure out precisely how much dry cooling will add to the total cost of the plant. Engineers, he explained, are struggling to optimize the design to minimize costs and energy efficiency losses that come with dry cooling. A U.S. Department of Energy report to Congress in January showed dry cooling adds between 2 and 10 percent to the cost of making electricity at solar thermal plants. The report said that during the hottest hours, dry cooling can reduce the output from a solar thermal trough plant--similar to the design for Genesis--by almost 18 percent. Florida-based NextEra, which last month began public stock trading on its own, separately from parent company FPL Group, has a power purchase agreement with Pacific Gas & Electric. Stengel said the company hopes to win both an Energy Commission license to build the plant and California Public Utilities Commission approval of the power purchase deal in time to break ground before the end of the year. If it can do so, it could get a 30 percent federal grant to help cover construction costs under the American Recovery and Reinvestment Act.

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