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| Solar Electric Division >> | January, 2008 | |
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Preliminary Program AvailableExhibit Space AvailableSolar Success Dealer/Installer Training EventReceive specific equipment training from several BOS manufacturers and learn to run your business more effectively! Have you activated your on-line membership account?
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In this Issue:
“The Come Back Kid with a Sunny Face” by Arnold Leitner, Chair, Solar Electric Division In 2002, when I authored the U.S. Department of Energy study, “Fuel From the Sky”, I made a strong case for concentrating solar power (CSP). But not even I would have predicted that in 2007, only five years later, CSP would stand in the zenith of public attention. In Spain, a 10 megawatt (MW) power tower, “PS-10”, went online and two 50 MW parabolic trough plants with large thermal energy storage capacity, “Andasol I and II”, are under construction. In the U.S. “Nevada Solar One” added another 64 MW to 354 MW of parabolic trough generation in this country. Numerous CSP companies, including my own, SkyFuel Inc., entered the U.S. market—half of them Spanish off springs, the rest venture-funded companies. PHOTO International called the rise of CSP in 2007: “The Sparkling Giants Awaken”. Even Google’s “RE<C” zero-carbon energy initiative put its primary hopes in CSP. Concentrating solar power is the “come back kid” of the renewable energy industry. There are four primary ways of concentrating solar energy (see article on “Concentrating Geometries” below), which include line concentrators such as parabolic trough and linear Fresnel and point concentrators such as dish systems and power towers. Each technology and its proponents are vying for attention and projects. Parabolic trough is the proven veteran and the workhorse of the Spanish market. In the U.S., however, venture firms view parabolic troughs as too expensive with little cost reduction potential and have left the technology to the incumbents such as Abengoa, Acciona/Solargenix, Solel, or Solar Millenium. Only SkyFuel, my company, is a venture-backed company in this space. Dish systems, long a favorite, also appear to have lost the early interest of venture firms. Not surprisingly, venture-backed companies are working on new ideas or revisiting old ones, such as linear Fresnel: Ausra, Novatec Biosol, SkyFuel and Solar Power Group (“SPG”) or power towers: BrightSource and eSolar. Generally, linear Fresnel systems generate low-temperature steam directly in the absorber tubes or by generating flash steam from heated, pressurized water. These low-temperature steam systems are primarily suitable for industrial process heat, but this not the reason companies are pursuing these technologies; their goal is to ultimately use these systems for power generation. Indeed, Ausra has announced a 177 MW project of this design. SkyFuel, also developing linear Fresnel, uniquely focuses on a higher-temperature Fresnel. (continued below). |
SOLAR TODAY Magazine January/Feburary 2008 Features >>- Advancing a Market for Zero-Energy Homes ASES’ Green Collar Jobs Report“Renewable Energy and Energy Efficiency: Economic Drivers for the 21st Century”
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All the present low-temperature linear Fresnel concentrators are of very similar design and maturity. Ausra and SPG employ elastically bent glass mirrors, while Novatec Biosol uses flat glass—the classic linear Fresnel idea. SPG and Novatec Biosol both use a secondary concentrator in the receiver. On the power tower side, several companies are actively pursuing this concept: Abengoa Solar (until recently known as Solucar), eSolar and BrightSource. Abengoa Solar originally pursued a high-temperature air-cavity receiver at PS-10, but then opted for a lower risk, simpler pressurized water receiver. However, PS-10, which went online in summer 2007, showed an output much lower than expected. This exemplifies the challenges of new CSP technology even when it is based on decades of power tower R&D, such as “Solar One” and “Solar Two” in the U.S. and on the various power tower systems at the research facility in Alamaria, Spain. eSolar and BrightSource each explore variations of the power tower design with a number of power towers sharing one central power block. The idea is to reap the advantages of a centralized receiver while introducing redundancy and a lower tower height. The year 2008 will be a deciding year for CSP when companies respond to solicitations for renewable energy in the American Southwest. The industry has certainly geared up in expectation of developing hundreds and thousands of megawatts of capacity. But two big clouds remain before the Sun in 2008. First, the 30% solar investment tax credit was not extended. Second, CSP companies have yet to test the willingness by utilities to pay for more renewable energy from CSP above and beyond the current contracts. In 2007, investors, the media and politicians where assailed with a confusing plethora of CSP technologies: dish engine, power tower, linear Fresnel and parabolic trough. The confusion was exacerbated by discussions of low temperature and high temperature systems. The reality is that CSP geometries and the temperatures at which they are suited for operation are related, and in this way easy to understand. All CSP technology starts with the following observation, first credited to Sir Isaac Newton: a parabola perfectly focuses parallel rays of light, shown in Exhibit 1 below. While we recognize that the rays of light from the sun are not truly parallel, this observation remains the foundation of CSP. Exhibit 1: Parabolic shape focusing parallel rays of light to a common point
Sir Isaac’s observation is shown here in two dimensions. In order to focus meaningful amounts of solar radiation it must be extended into the third spatial dimension. Perhaps the most intuitive way is to extend the parabolic shape out of the page, creating a “trough.” This is the parabolic trough geometry, shown below in Exhibit 2: Exhibit 2: Parabolic trough CSP geometry
As the size of the trough increases (current-generation designs approach 20 feet in aperture width!) the support structure must dramatically increase in strength to resist forces generated by the wind. The most common way to eliminate this problem, while maintaining the extension of the parabolic shape out of the page, is to break the parabolic shape into a series of linear facets. Each of these linear facets are then projected on to the ground creating an approximation of the parabolic shape with the same aperture width, but with much less exposure to the wind, shown in Exhibit 3 below. This is geometry is known as the linear Fresnel. Linear Fresnel and parabolic trough are the most common “line-focus” geometries. Exhibit 3: Linear Fresnel CSP geometry
An alternative way to bringing the parabolic shape shown in Exhibit 1 into the third spatial dimension is by rotating the parabolic shape around axis of the focal-point of the parabola, making a “dish” shape. This is the geometry of satellite dishes, and the dish engine CSP geometry, shown in Exhibit 4 below: Exhibit 4: Parabolic dish, or dish-engine CSP geometry
Similarly to the parabolic trough geometry, the dish geometry becomes ungainly and structurally limiting as its aperture becomes large. Like the parabolic trough geometry, the dish geometry can be separated into an array of facets, which are then projected on to the ground below. This is the power tower geometry, shown below in Exhibit 5. Exhibit 5: Power tower CSP geometry
With each of the geometries discussed, a range of concentration ratios and operating temperatures are defined. The concentration ratio is defined as the area of the reflective surface divided by the area of the absorber, or receiver. Thus, the higher the concentration ratio, the more intense the sunlight is that strikes the receiver. From a thermal efficiency perspective, higher concentration ratios are generally better – as more energy is absorbed by the receiver for each unit of energy that is lost by re-radiation and conduction. From an optical perspective, lower concentration ratios are generally preferred. The sun is not a laser, and delivers radiation over its entire angular width of about 0.5°. This “cone-angle” of the sun puts fundamental limitations on the optics of solar concentrators. The higher the concentration ratio of a collector, the more optical losses must be tolerated to maintain focus on the receiver that is small relative to the reflectors. These errors are due to the increased distances over which the “cone-angle” of the solar rays propagate causing more rays to miss the receiver, as shown in exhibit 6 below. Exhibit 6: Incident solar rays distributed over the sun’s angular width resulting in rays missing the receiver. The further the rays must travel after reflection, the more will miss the receiver.
The point-focus geometries dish-engine and power tower, can achieve very large concentration ratios due to their single focal point – on the order of 10,000:1. The high thermal efficiency that comes with such a concentration ratio favors high-temperature system designs. Experimental gas-receivers in Spain have achieved 1000°C in point-focus configurations. The line-focus geometries, linear Fresnel and parabolic trough, have larger receiver areas than the point-focus geometries, resulting in concentration ratios that are much lower than those seen in point-focus systems, typically on the order of 100:1. Line-focus concentrators used for power generation are typically designed to operate in the 250-400°C range, although technology improvements are indicating that line-focus collectors may be able to efficiently collect solar energy at temperatures of 500°C or higher. The balance between optical efficiency, thermal efficiency and operating temperature are what drive selection of concentrating solar power geometries. These trade-offs are fundamental, implying that all of the major CSP geometries have clear strengths and weaknesses – it still remains to be determined which geometry will prove best at optimizing for the metrics that really matter in renewable power generation: cost per unit of delivered energy, and dispatchability (on-demand power). On 29 November 2007, Alexander Karsner, Assistant Secretary for Energy, announced the awards of the U.S. Department of Energy, “DOE Concentrating Solar Power 2007 Funding Opportunity”. Nine companies were invited for contract negotiations on grants for various technologies. Here is a review of the technologies DOE will fund: Mirrors 3M returns to the CSP space with interest in a cleanable hard coat of silvered polymeric mirrors indicating the company’s interest in returning to reflective film such as ECP-305+ which 3M stopped producing because of problems with the film and insufficient market. Solucar (now Abengoa Solar) is setting out to develop a polymeric reflector from scratch. The company is a user of reflective films and is seeking a technology of its own. The only commercial product for reflective films designed specifically for use in solar applications is ReflecTech™, a silvered film produced and marketed by ReflecTech, Inc. The two market entrants into the reflective film market seem to prove the thesis by some market experts that a replacement of silver glass mirrors in concentrators will be an important next step for the CSP industry. PPG Industries is seeking to develop a glass mirrors that include an “inorganic coating that protects the mirror from chemical attack, an organic coating that protects the mirror from mechanical attack” in an effort to provide an alternative to current offerings in the glass mirror market. Parabolic Trough Technology Alcoa, the aluminum maker, took note of the state-of-the-art extruded aluminum space frame now in use at “Nevada Solar One” and appears ready to improve on that design with “optimization of the collector assembly, including reduced reflector weight, improved supporting structure joint design, and increased reflector stiffness.” The industry is likely to see an offering for an aluminum space frame from Alcoa. Abengoa Solar is also asking DOE for funds for the development of an innovative parabolic trough concentrator with “major impact” on its cost. Solar Millennium is developing a “high-performance, low-cost parabolic trough collector” that will be designed with the use of a molten-salt heat transfer fluid in mind. These three companies apparently believe that the cost reduction curve for parabolic trough is far from flat. Linear Fresnel Technology SkyFuel received the only DOE award related to linear Fresnel technology. SkyFuel will develop a high temperature linear Fresnel CSP system. The DOE indicated that it believes this technology has the potential to meet its own 2020 cost target of 5 cents/kWh. SkyFuel’s Linear Power Tower (LPT) is different from all other linear Fresnel systems currently under development in that it focuses on the use of a high-temperature molten salt receiver for higher efficiency and ability for direct thermal energy storage. Dish Engine Systems Infinia Corporation and Brayton Energy are developing dish engine systems, which are believed to be able to eliminate many of the problems associated with previous generation dish systems. Infinia is developing a free-piston Stirling engine which is hoped to reduce engine maintenance requirements, and Brayton Energy is implementing compressed air energy storage, bringing storage to dish engine technology. Molten Salt Heat Transfer Fluid Three solicitations are for the use of molten salt as heat transfer fluid, indicating that CSP technology is (again) ready for higher temperature, which brings the virtues of higher power cycle efficiency and compact and cost effective storage. (Mineral oil-based heat transfer fluids like the venerable Therminol VP-1 are limited to upper temperatures of 400º Celsius (750º Fahrenheit)). Abengoa Solar, who took away three awards, is focused on molten salt heat transfer fluid research with an eye on parabolic trough collectors. Rocketdyne picks up where Solar Two—the molten salt power tower—left off in 1999 by returning to a high-temperature receiver for a power tower. Rocketdyne also seeks funding for a molten salt pump—a critical component for moving molten salts. “Nevada Solar One” Comes Online The first large concentrating solar power plant in the United States built in nearly 15 years came online in June, 2007 in the form of the Acciona/Solargenix 64MW parabolic trough plant outside Boulder City, Nevada. “Nevada Solar One” is the third-largest solar power plant in the world behind SEGS VIII and IX, each 80 megawatt (MW) which are operating in the Mojave Desert in California. Nevada Solar One covers over 300 acres, uses over 19,000 evacuated receiver tubes, and over 3.5 million square-feet of curved mirrors. The construction work force, which broke ground in March of 2006, required to assemble this massive project ranged from 400 to 850 people. This newest parabolic trough power plant is a major technical success, improving substantially on the technology used in the past Luz-built parabolic trough plants. The aluminum support structure used at Nevada Solar One is both lighter, easier to assemble and more optically accurate than past designs. Further, a new generation of receiver tubes from Schott and Solel used at Nevada Solar One have substantially improved thermal performance relative to past designs. The success of Nevada Solar One is shared by the entire concentrating solar power industry, as it has played a key role in the resurgence of interest by utilities and investors in deploying the technology at a large scale. Summary of CSP Projects in the United States In recent years a number of large power-purchase agreements (PPA) between utilities and suppliers of concentrating solar power (CSP) projects have been announced. The first of the current wave of solar power projects was announced by Sterling Energy Systems (SES) in 2005. SES is pursuing two large solar power projects utilizing its dish engine technology. The first, a 500 MW project selling to Southern California Edison for project in California called “Pisgah.” The second project is a 300 MW project with San Diego Gas & Electric to be located in the Imperial Valley. Solel, an Israeli supplier of parabolic trough technology, has announced the “Mojave Solar Park” with a 553 MW 25-year PPA with Pacific Gas and Electric. BrightSource Energy has filed an application for construction with the California Energy Commission for its 400 MW Ivanpah power tower project. BrightSource Energy is associated with Luz 2, an Israeli company founded by members of the original Luz company responsible for the construction of the 354 MW SEGS plants in California. BrightSource and Luz 2 develop a power tower technology they call “Distributed Power Tower” (DPT). Ausra, the American arm of Australia’s Solar Heat & Power, has filed for construction permits with the California Energy Commission for its San Louis-Obispo County-cited “Carrizo Energy Project. The Carrizo Energy project is a 177 MW. Ausra is negotiating a PPA with Pacific Gas & Electric for Carrizo. Ausra employs a low-temperature linear Fresnel concentrator design. Inland Energy has filed an Application for Construction for “Victorville II”, a 50 MW solar-combined cycle hybrid using parabolic trough concentrators. Interview with Dr. Newton Becker by Arnold Leitner Dr. Newton Becker is a founding father of the modern solar power industry. As the founding investor and chairman of the board of Luz International, Dr. Becker helped conceive and develop the first Solar Energy Generating System (SEGS) plants, which were located in California’s Mojave Desert. These nine parabolic trough solar power plants with 354 MW of capacity have generated millions of megawatt-hours of clean electricity for Southern California since they went online in 1985-1990. Dr. Becker recently sat down with ASES to discuss issues currently impacting the solar industry. ASES: In 1990 the last of the Luz parabolic trough plants at Harper Lake, the Solar Electric Generating Station (SEGS) IX was commissioned preceding an environment of plummeting oil prices. It was the end of a stunning success story for concentrating solar power. Today with oil prices near $100 per barrel and natural gas well over $7/mmBtu we are in an era of high fossil fuel prices and Concentrating Solar Power (CSP) is coming back as a viable, cost effective alternative to fossil fuel for grid based electric power generation. How do you compare today’s environment with the eighties and early nineties? Dr. Becker: From a fossil fuel price basis it is very similar to the 80s. Solar is a fuel source and competes against natural gas on price. Natural gas is linked to oil to a lesser degree. Oil prices are not set by a free market, but by a cartel, OPEC. A cartel artificially raises or lowers prices—at any time. And this is a fundamental problem for solar ASES: This is because CSP has a high capital cost and, therefore, needs a decade or more to recover its cost? Dr. Becker: Exactly. After the capital cost of building the plants is recovered, the fuel cost of solar is an essentially free domestic source of energy! But a sudden drop in fossil fuel prices, even for a relatively short period, can destroy the industry of building new solar electric generating plants. It is like building an apartment house with a long-term mortgage. If the neighborhood declines, the rents will decline and the ability to pay off that mortgage evaporates. Furthermore, no construction company will build in that neighborhood because there would be a negative return on investment. This is what happened to Luz. ASES: So, what is the remedy? Dr. Becker: There are two major solutions. One is for Solar Companies to build only with guaranteed fuel prices for a length of time long enough to pay off the mortgage, which is about 12 to 15 years depending on the project. This is a necessary condition for the investors, who otherwise would not invest. However, Luz started with long term contracts for its first seven projects, and the California PUC decided they were too long and possibly too expensive and stopped giving long term offers (Standard Offer No 4). That decision by the California PUC, turned Luz, a construction company, and the investors in SEGS 8 and 9 who did not have long term guaranteed fix price contracts into speculators in oil futures. Solution two, in the absence of long-term contracts, the industry would need floor price guarantees from the Federal government. The states with enough sun cannot afford to potentially subsidize solar electricity sold in other states. Energy independence and environmental protection are issues of national security. It is the Federal government’s role to step in here. For the solar industry to survive temporary downward spikes in fossil fuel prices, it needs long-term, fixed price contracts to recover its cost. After that the plants will continue to run for decades—almost free. But first we need long-term fixed price contracts or guaranteed floor price contracts. ASES: A number of economists have analyzed this problem and proposed a floor price guarantee on fossil fuel prices similar to a farm commodity floor price guarantee. The idea is that if fossil prices drop below a certain level, then and only then they receive the difference in a fuel subsidy. Dr. Becker: This is one very effective way of doing it and one I have written about. The advantage of this method is that it applies across the economy. But, there is another reason for a floor. Eventually renewable energy will dampen demand for fossil fuels and bring down prices. I fully expect fossil fuel prices to spike downward in the future for two reasons. One will be caused by OPEC who will want to drive out renewable technologies as competitors. Most renewable technologies face economic challenges similar to solar. Many of them have high capital costs that need to be recovered over many years. Two will be when “plug-in hybrids” or “all electric” cars become common on the road, the demand for oil will be reduced and prices will drop in accordance with the law of supply and demand. But it is not all about national security and economics to embrace Solar a carbon free renewable. It is also about combating global warming. We have an emergency today. Let’s not be persuaded by undocumented malarkey, mostly promoted by the fossil fuel industry paid “scientists” claiming that carbon dioxide is not responsible for global warming, the overwhelming evidence is in. We are heating the planet by burning fossil fuels. ASES: Some argue that government subsidies would only support high priced solar technology, which has no potential to come down in cost. Dr. Becker: Luz experienced the learning/innovation cost curve from the beginning. Our first systems produced solar electricity at about 24 cents a KW hour. The next systems at 15 cents, we were working on a new design, which would have brought the cost down to 6-8 cents, when the spike down in oil and natural gas prices made it impossible for the system we were building to be cost effective. We could not sell those syndicated systems then until year-end when they were almost complete. Our last system was about half complete when we filed for voluntary bankruptcy. I see new solar companies today with designs that would reduce the costs from Luz design, and I believe we are still at the beginning of the innovation curve. At Luz we created technology as we went. Today, there are major cost improvements possible on structural design, reflective surfaces, receiver pipes, etc. It’s all just up to imagination and finding out nature’s secrets. Twenty years ago Luz was state-of-the art, but we knew then that we were just at the beginning of the innovation curve. The innovation cost curve in Solar has a long way to go before it flattens out. But innovation must go beyond performance and capital cost; it must reach into financing, supply chains, turbines, delivery systems (grids) etc. But all of this faces the threat of sudden interruption—if fossil fuel prices just drop precipitously as it did in 1991. ASES: But how do we bring this energy to market? Dr. Becker: We need a very good [electric] grid. This not only allows us to move solar power from the Western states with sun to the Eastern states with little sun, but also to meet the peak demands in the East with solar power from the West, and wind power from all over the country, etc. ASES: Scientific American in its January 2008 issue had an article that stated such a vision? Dr. Becker: I am glad to hear that. Look, we in California are getting peak load hydropower from the Portland/Seattle area about a thousand of miles away. That grid was built about fifty years ago. The Grid technology is out there; it takes a capital investment to make it happen. One great advantage to our country is that it will create jobs and businesses that will not only create energy and energy independence, but will also create stable costs in electric energy and taxes for the state and Federal governments. This is opposed to importing oil, which creates; very few jobs in comparison and no taxes, but does create global warming and a balance of payment problem for our country. ASES: Is this a place for the federal government to come in? Dr. Becker: Yes, states cannot do this alone. That applies to; providing a price floor for fossil fuels, loan guarantees, special interest rates for solar and the design and construction of a national grid. ASES: In this world that you envision will it be easy being green? Dr. Becker: Yes, I have been living “the green future” for the past eleven years. For six years I leased the EV-1 [the electric car built by General Motors] and l loved it—but they took it away from me when the lease expired in 2002, which is when GM closed down their EV program. Because I helped build the SEGS plants as Chairman of Luz, which served the southern California grid where I live, I think of my electric cars as running on solar energy from Luz. By the way electric cars do not have crankcases that use oil. They only need lubrication. So my life has been carbon free for over a decade. I see a future of electric cars powered by electricity produced from Solar and Wind and other global warming benign renewable energies. ASES: Thank you for you leadership and inspiration in solar energy and thank you for the time to share your thoughts. Dr. Becker: It was my pleasure. And good luck to everyone in the solar industry. These are exciting times.
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Copyright © 2008 American Solar Energy Society • 2400 Central Ave., Ste. A, Boulder, CO 80301 P: 303.443.3130 • F: 303.443.3212 • ases@ases.org • www.ases.org |
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