No survey of utility scale solar thermal power companies is complete without mention of Solel Solar Systems Ltd., headquartered in Israel with operations in Spain and the USA. In December 2007 Solel’s purchase power agreement (PPA) with Pacific Gas & Electric Co. was approved by California’s Public Utility Commission for a solar thermal plant with 553 megawatts of output. Even without thermal storage to optimize the solar energy, the “Mojave Solar Project” is expected to produce 1,388 gigawatt-hours of power per year.
|A Solel parabolic trough faces due west,
capturing the last energy of the day.
Solel has experience supplying components for the solar thermal installations at Kramer Junction, which for over 20 years have produced up to 350 megawatts of output, and remain the largest solar thermal electric power complex in the world.
More recently, in 2006, Solel supplied Spain’s Sacyr-Vallehermoso with solar receiver systems to build a 150 megawatt solar thermal plant. Last month, Solel signed an agreement to supply Spain’s Aries Solar Termoelectrica, S.L. , with systems for a 100 megawatt solar thermal plant.
There are several ways to harvest solar thermal energy to produce utility scale quantities of electricity, and at least three variants remain cutting edge: There is the “power tower” design favored by Brightsource Energy – where a central boiler is placed on a tower surrounded by hundreds of two-axis tracking mirrors that each reposition themselves continuously to track the sun and keep it focused on the boiler. This design has the advantages of centralized plumbing, and as well, the mirrors in the solar field can be placed on individual poles which simplifies site preparation. Another promising design is being pioneered by Ausra, where ten mirrors, all on a north-south axis and turning on a single-axis tracker, focus the sunlight onto a single tube that runs in the air above all of the mirrors and parallel to them. This design also economizes the amount of plumbing required, and requires far fewer tracking systems which are only single-axis.
Solel’s solar receivers use what is known as the “parabolic trough” design, where each mirrored trough is curved to reflect the sun’s rays onto a tube that runs lengthwise above each trough at the focal point. These receivers are also single axis, running north to south. They turn to face the sun when it rises in the east, and reposition themselves to point at the sun throughout the day so they are facing west each day at sunset. While this design requires more materials than Ausra’s design, it is time-tested, and may be more efficient, since a heat exchanger is positioned immediately above each reflecting mirror. Solel’s recently launched “UVAC 2008″ solar receiver system captures sunlight and converts it to heat for clean power generation with 20% less heat loss than other receivers in the market,” according to testing by the National Renewal Energy Laboratory of the U.S. Department of Energy in October 2007 – although it isn’t clear if Ausra’s design was included in that test.
With decades of experience in this market, and recent 100+ megawatt orders, Solel has as much experience as anyone in solar thermal technology. When we asked spokesperson Vanessa Lindlaw when the Mojave Solar Project would break ground, she stated they would be filing at the California Energy Commission by mid-year, and also were waiting to see if the U.S. Federal Investment Tax Credit would be renewed. Best case, the Mojave Solar Project could come online by 2011. It will consume nine square miles of desert and cost about $2.0 billion. While this equates roughly to $4.0 million per megawatt, and that is somewhat on the high side compared to conventional power plants, the complete absense of fuel expenses means Solel’s project should still be able to profitably sell electricity at around $.10 per kilowatt-hour.
If this 553 megawatt plant goes online, it will provide a significant share of California’s electricity consumption, at least during peak daytime usage. California’s electricity draw varies between around 50 gigawatts at peak and under 20 gigawatts at night. During mid-day, this single plant will probably be delivering about 1.25% of California’s entire electricity production. But as the electric age dawns, we’ll need more power than ever, if electrons are to begin to replace petroleum.