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Renewables News Highlights; Are Solar Stocks Too High?; Public Co. Highlights; Concentrating Solar Power: The Other Side of Solar; Conversation with CSP Expert, Fred Morse & CSP Company, Stirling Energy Systems.
Issue 31: November 2005
Concentrating Solar Power:
The Other Side of Solar
Concentrating Solar Power (CSP) suddenly entered the renewable energy limelight over the last couple of months and, although there is only one publicly-traded company in the area, we thought you would want to understand this promising energy sector.
CSP technology has been being quietly perfected over the past 25 years, and with three recent huge contract announcements, it is finally coming into its own. As we reported in the September issue, Stirling Energy Systems (SES) won contracts with utilities Southern California Edison (500 MW) and San Diego Gas & Electric (300 MW) to place a total of 32,000 solar dishes in the California desert. And Solargenix Energy won a contract to build a 64 MW plant in the Nevada desert. There are projects in the works in many countries around the world including Spain, Australia, India, Mexico, Israel, Egypt, and Morocco.
The projects are catalysts for the widespread adoption of solar thermal technology. Because they are so large they could create economies of scale and drive costs down to the point where CSP prices could be competitive with fossil fuels within the next decade.
Said Mark Mehos, program manager for the US Dept of Energy's National Renewable Energy Lab's (NREL) CSP program, "Given today's natural gas prices combined with tax incentives offered in the recently passed energy bill, utilities and investors are showing a lot of interest in the development of large-scale concentrating solar power plants. This is the first in line of a string of new large-scale domestic and international CSP projects."
What is CSP and why is it important?
Until now, the attention in the solar sector has been on photovoltaics (PV), which, when placed on rooftops or integrated into windows or walls of buildings, produces distributed electricity by using the "light" from the sun. The PV side of the industry has received greater government support and has the largest players, many of them now publicly-traded, profitable companies.
The CSP side of the industry makes use of the "heat" from the sun (thermal energy) and consists of large centralized utility-size installations. Unlike PV, CSP does not use silicon. Raw materials aren't a problem - they are common components such as glass, steel, gears and engines. CSP power plants are much more efficient and can produce very large quantities of solar energy.
The two types of solar technology complement each other - both are necessary to transform our energy portfolio away from fossil fuels and toward renewable energy.
How do CSP plants work? By focusing mirrors on the sun, they convert the sun's energy into high-temperature heat, which is then channeled through a conventional generator, turning the heat energy into electricity.
CSP systems can be sized for village power (10 kW) or grid-connected applications (up to 100 MW). They require direct sunlight, found in deserts around the world. There are several technologies within CSP: some can store energy for later use and can be combined with natural gas, giving them the ability to provide "dispatchable" power - whenever the utility needs it.
That's a key advantage of CSP - utilities feel comfortable with the technology because it closely resembles conventional centralized power plants - sharing much of the same equipment and providing energy on demand. CSP plants simply substitute the concentrated power of the sun for the combustion of fossil fuels; it's an evolutionary, rather than a revolutionary, technology. Thus, CSP can be easily integrated into today's central station-based electric utility grid, making CSP the most cost-effective solar option for large-scale electricity generation.
CSP fits the business model utilities feel most comfortable with. They can draw energy from big plants and simply sell it to customers, as opposed to PV, which reduces the energy utilities have to sell, or wind, which is intermittent technology and not always available.
And the solar CSP resource is huge: covering nine percent of Nevada with CSP power plants would provide electric power for all of the U.S.
CSP plants are not new - a 354 MW plant called SEGS (Solar Electric Generating Systems) has been operating in the California desert since the mid-1980's. All these years later, the plant continues to function at or above its design specifications, and it provided crucial dependable power during the California energy crisis.
Since the construction of the SEGS plants, the CSP industry has made many technological advances in system performance, reliability, durability, and cost. While early CSP plants generated power at about 35¢/kWh (in 2001 dollars), the price is now 11¢/kWh. It is expected to fall below 8¢/kWh within five years and below 5¢/kWh by 2015, when it will be fully competitive in global mega-markets.
How do CSP plants work?
Conventional power plants often use fossil fuels to boil water; the steam then rotates a large turbine, activating a generator that produces electricity. CSP substitutes the sun as the heat source. There are four main CSP technologies today: dish/engine, parabolic-trough, CLFR and power tower.
A dish/engine system looks like a large mirrored satellite dish. It collects and concentrates the sun's heat onto a receiver, which absorbs the heat and transfers it to a gas in an engine. The heat causes the gas to expand against a piston or turbine to produce mechanical power, which is used to run a generator to produce electricity.
Dish systems require no water and can be used as distributed or centralized energy. Individual units, which can range from 9-25 kW in size, can be located in remote areas, such as throughout the developing world, to pump water or provide electricity. Although dishes can't store thermal energy, the most urgent need is for peak electric power, which dishes provide most cost-effectively.
There are a handful of dish/engine companies worldwide. Stirling Energy Systems (SES) is most notable but there are others in Europe and Australia.
In parabolic-trough systems, long parallel rows of U-shaped mirrors are tilted toward the sun, focusing the light on a pipe that runs down the center of the trough. The sunlight heats oil that flows through the pipe, which is used to boil water in a conventional steam generator to produce electricity. A trough plant consists of many rows of troughs that are aligned north-south in order to track the sun as it moves east to west. Troughs can store energy for later use and can be integrated with conventional coal-fired plants.
There are 3 major trough developers: Solargenix Energy, which is building the 64 MW plant in Nevada; Solel, an Israeli company; and a German company, Solar Millenium, which is developing the project in Spain. Solar Millenium (S2M.MU) recently launched its IPO and is the only publicly traded company in CSP.
CLFR (Compact Linear Fresnel Reflector) technology is a hybrid of Fresnel and Trough technology, and is on the brink of commercialization. Think of it as a super-trough; it is simpler and cheaper than parabolic troughs, avoids many of the problems inherent in other CPS designs, and can store energy very cost effectively.
The reflective surface is ten times larger than parabolic troughs - individual mirrors are almost flat and laid in long rows edge to edge, covering the ground with densely packed mirrors. Whereas the mirrors in a parabolic trough all focus on one line in the center, with CLFR, rows of mirrors can focus on alternating parallel receiver lines, and can get out of each other's way at low sun angles. This almost eliminates shading and blocking while maximizing mirror ground coverage.
The result is that twice the energy and three times the peak power can be collected per plot of land. CLFR also operates at lower temperatures, which reduces the complexity and cost.
Power tower technology, which has yet to be commercialized, uses a large field of mirrors to concentrate sunlight onto the top of a tower, where it heats molten salt that flows through a receiver at the top. The salt's heat generates electricity through a conventional steam generator. Since molten salt retains heat efficiently, it can be stored for days before being converted into electricity, making electricity available on cloudy days or in the evening. Tower technology is in the pilot phase now.
Trough plants and power towers are large industrial facilities. Although advances are being made, the heat transfer fluid used in parabolic troughs is a hazardous, volatile organic compound, and fire can be an issue. Therefore, facilities must be sited away from inhabited areas, which increases transmission costs. Another disadvantage to parabolic troughs is the land underneath must be kept free of vegetation in order to prevent fires. Herbicides are used to control vegetation growth.
CLFR eliminates most of the problems associated with parabolic trough plants: no flammable liquid is used which can cause brush fires; the troughs are raised off the ground and thus don't disturb low-lying vegetation, which means the land doesn't have to be sterilized with herbicides. A robot automatically washes the mirrors so the land doesn't have to be accessed for routine maintenance.
Power towers use salt and since they are high above the ground, the ground doesn't need to be sterilized. But tower height can be an aesthetic problem and they do require the most land of the three technologies. Both require large amounts of cooling water (as do conventional steam plants) - a problem in desert environments.
Dishes use the least amount of land; don't require water, toxic fluids, or scrubbing of the vegetation. They are the easiest to site. They can store electrical energy through batteries, flywheels and other devices, but they can't store thermal energy.
CSP power plants can be built quickly - within a year or two - and can thus be linked more closely to demand than conventional power projects. They also avoid the lengthy permitting process that fossil fuel plants must go through. Dishes and towers don't have to apply for air permits because they use no fuel.
Learn more: http://www.eere.energy.gov/solar/csp.html
Major CSP Projects:
Projects Under Development: