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. (Photo: Solel) |
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.Â
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.
February 20th, 2008 at 11:05 am
I’m surprised that anyone who claims knowledge of electrical generation would claim that solar thermal “will replace petroleum.” Petroleum is used for transportation - very little (especially at today’s oil prices) is used to produce electicity. Unless an alternative energy producer can produce power on demand, such power is virtually useless in meeting the needs of consumers and will never allow the closure of even a single fossil fuel plant, as Denmark has shown with it 25% wind power generation, of which it can use barely 12%, making it the most inefficient and costly electrical power generating apparatus on the planet. Ausra can store its energy and produce it during peak demand. Unless the other can do this, they are doomed, regardless of how “efficient” they may claim to be.
February 20th, 2008 at 1:08 pm
Kent: The point is not that solar thermal will replace petroleum directly, the point is that electricity can replace petroleum. For automotive applications, moving to solar thermal power does have the potential to directly offset petroleum consumption - to the extent cars run on electricity instead of gasoline.
Your comment about storage is absolutely correct - massive electricity storage is one of the only ways to load balance intermittant sources of electricity such as wind and solar. Will Ausra’s solution work? We don’t know yet. But whether it’s thermal energy stored in the form of steam ala Ausra, or molten salts which other solar thermal companies are exploring, something will be necessary.
There are other solutions to storage and load balancing to consider. Not only might electricity be stored for night-time use at the solar thermal utility, but electricity may also be stored via massive distributed systems at the substation level or even at the commercial building or residential level - Gridpoint is pioneering this technology using batteries and there are several other companies right behind them.
Finally, not generally acknowledged is the huge potential for solar and wind energy to get load balanced by large hydropower. It is relatively easy to activate or deactivate one turbine at a time in a large hydroelectric station. When the sun is shining, turn off the turbines - when the sun goes down, turn them back on. Large scale solar thermal installations can reduce the rate at which water is released from a hydroelectric plant, and the ability to turn on and off these turbines can provide load balancing at the grid scale.
March 16th, 2008 at 11:04 am
Ausra is not going for a north-south mirror allignment in their 177 MWe plant. Even though it yields slightly more energy than an east-west mirror allignment, it has the unacceptable flaw of very poor winter performance (=yield). It’s useful if you want to deal with summertime air conditioning and stuff but in terms of powering a significant portion of nationwide electricity (e.g. through HVDC from the southwest to other states) an east-west mirror allignment is far more useful because of very consistent load following performance.