Ausra – Solar Thermal Power

Utility scale solar thermal power is something you still don’t hear much about, but along with photovoltaic power, it is a big part of the reason solar power is possibly the only source of renewable energy that is not only absolutely clean and sustainable, but capable of exponential growth for decades to come. And Ausra, headquartered in Palo Alto, California, has perhaps the most promising solar thermal design we’ve ever seen.

Ausra’s “solar field” of reflectors.
Note the heat exchanging tube overhead.

Solar thermal power uses mirrors to reflect sunlight onto heat exchangers, in order to heat a thermal transfer fluid to drive a turbine, which turns a generator to produce electricity. Only about 500 megawatts of solar thermal power capacity exist in the world today, most of it at Kramer Junction in California’s Mohave Desert.

Compared to total worldwide energy production, solar thermal electricity production is negligible, only about one 20th that of photovoltaic energy production, which itself represents less than one-twentieth of one percent of worldwide energy production. But this is about to change, and solar thermal technology will race photovoltaic technology neck and neck, as together they grow to a significant share of global energy production.

There are three basic ways to concentrate solar energy – one is a “power tower” where a boiler sits atop a tower surrounded by 2-axis tracking mirrors that each individually move each day to reflect the sun’s light onto the boiler. Another design is a field of parabolic mirrors, each of them equipped with a 2-axis mechanism to track the sun all day, with each of them having a heat exchanger positioned at a single reflective focal point a few feet away from the center of the dish. Finally, the most cost-effective design appears to be the parabolic trough, where only a single axis tracking mechanism moves curved, mirrored troughs each day from east to west, with a heat exchanging tube suspended at the reflective focal point above each trough. All of these designs have been tried with some success.

What Ausra has done is taken the parabolic trough concept, with the simpler single-axis tracking mechanism, but designed a solar field where one heat-exchanging tube, running north to south, is suspended several meters in the air above several lengthwise tracking mirrors. Because the heat exchanging tube is further away from the mirrors, they don’t need to be as curved, reducing costs. Because several mirrors share one tube, there is a greatly reduced need for plumbing. And single-axis rotation, simply moving east to west with the sun, requires far less mechanical elements, and far less maintenance.

Yesterday we had a chance to speak with John O’Donnell, a physicist who is now EVP of Ausra. He explained several additional reasons why Ausra’s design is destined to become the standard for solar thermal power stations. Each of the mirrors is designed just small enough to fit in a standard interstate multi-mode shipping container. Each mirror requires just eight minutes to be manufactured on an automated production line. They are light weight and primarily require only flat glass and raw steel in their manufacture. The heat exchanging tubes are single lined and require far less maintenance than earlier designs. The heat transfer fluid is water; not molten salt, or some other expensive, corrosive, toxic substance – just water, of which nearly 100% is recycled. Ausra’s elegant, least cost design, according to O’Donnell, “has generated explosive interest around the world.”

Something we never would have guessed is that the incremental costs for building an oversized steam storage unit are not significant; O’Donnell noted both that the storage unit would not consume very much space, and even if it were built out to allow 20 hours of operation per day, it would add less than 10% to the cost of the entire power station. A clear advantage of solar thermal power is this ease in stretching the hours of operation into the evening when power consumption is heaviest. O’Donnell stated the current designs have a steam storage unit sized to stretch the daily hours of electricity generation through 8 p.m., which is when peak demand typically begins to subside. Ausra believes they can sell electricity using their technology for $.10 per kilowatt-hour; a price that is definitely competitive with today’s rates, especially during peak hours.

A brief report on solar thermal power would not be complete without noting the space required to generate electricity using this technology. In “California Land Use Choices” we estimated you can get 130 megawatts from a one square mile solar thermal power station. A utility scale photovoltaic power station of the same size would generate about twice that, but would cost far more to build. According to O’Donnell, the plant they are in the permitting phase for right now, to be located just south of Paso Robles in sunny Central California, is going consume exactly one square mile, and it is designed to generate 175 megawatts. Unlike biofuel, the land required to power the world with solar thermal or photovoltaic energy is simply not significant.

8 Responses to “Ausra – Solar Thermal Power”
  1. kent beuchert says:

    The notion that htere will be a “race” between solar thermal and solar photovoltaic is absurd. Solar thermal will quickly make those two crappy non-dispatchable technologies wind and photovoltaic (if one can even call them technologies) totally obsolete. It’s high time this country stopped rewarding shoddy quality electricity in the form of wind and photovoltaic with outrageous subsidies. Now we’ll have to spend a lot more tearing down those hideously obscene wind towers. The alternative energy movement has made a collossal blunder rushing to judgement, as if the pitifully infinitesimal amount of uncontrollable power we get from those two technologies would ever have made the slightest difference in overall climate changes. Our 1.8 cents per kilowatthour subsidies to wind amount to more than the total cost of nuclear power!!!!!

  2. Ed Ring says:

    Kent tell us what you really think. “Crappy non-dispatchable technologies” to describe photovoltaics when they can be baked into the windows? I think not.

    As for wind energy, I tend to agree with the scenicists like you. What do you think about wind turbines offshore? It would take 35 of the 5 megawatt turbines to compete with a square mile of solar thermal, correct? It comes down to the rate of return – solar thermal does seem to be more practical than wind generators. But in some climates wind generators probably can deliver a good return.

    You are certainly correct that adoption of carbon uptaking technologies may not affect our planetary climatological destiny, but if these alternatives can pay their way, why not deploy solar systems and achieve energy independence?

  3. Chris Saunders says:

    My father and myself have been considering the idea of an underground home for years in the past five years though i have been researching about solar power after much debate we have both decided we would like to pruchase enough land to put up a small solar farm being his house is paid for and i having over 150,000 in equity in mine we are both willing to sell and move to a nesscary site in order to acheive our goal i was wondeirng if by any chance you could point us in the best direction about doing so right now i am just touching bases with certain organizations that i think may find what i want interresting enough to help out

  4. Ed says:

    You might try somewhere that is southern enough to be fairly sunny even in winter, where there is still cheap land. It depends on how much power you want to sell, of course. A solar farm still has to get its electricity to market – and this is where things get complicated. Be careful jumping into a new industry, there is a lot of risk. You may want to post on our electricity forum – your question is a perfect topic there.

  5. Mel McFarland says:

    Chris Saunders seems to have a great idea-why not buy the mirrors and tracking equipment from Ausra, buy a small Rankine cycle turbine generator on the open market, buy enogh land for a small power plant, and start up your own utility? If enough of us did this, we could turn the fossil fuel companies into fossils themselves…

  6. Savan Mehta says:

    We are looking for a Solar Thermal Plant in India, most probably in western part of India. What kind of technology do i need to use, so that my project cost is not very high. also wht can be the business oppurtunitites considering Indian Market COnditions?

  7. Yermal Shetty says:

    There is a 40 MW solar thermal plant in operation near Jaipur, India. Savan Mehta can contact Rajastahn State Power Corporation Ltd. (Tel. (91-141)384055 to get information about the technology and the cost associated with such a plant. I hear that the project includes a collection area of 219,000 square meters to support the 40 MW solar thermal plant. The original project cost estimate for equipment was about $41 million.

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