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Wednesday, May 13, 2009
Making the desert bloom with solar flower power
Concentrating Solar Energy Technologies Explained
Q: What are the different types of concentrating solar energy technologies? Why are they limited to the southwestern United States? -- Bertha Z., Berea, KY
There are two main types of concentrating solar energy technologies: concentrating photovoltaics (CPV) and concentrating solar thermal (CST). Together they are commonly referred to as concentrating solar power (CSP), although sometimes CSP is used interchangeably with CST.
1. Concentrating photovoltaics (CPV) uses lenses or mirrors to focus or increase the sun's light on a photovoltaic solar cell or panel. This technology includes both a low-concentration approach, which increases the sun's magnification by less than 5 "suns," and high concentration approach, which can increase the magnification by hundreds of suns. High-concentration CPV uses focusing lenses to concentrate the sun's rays on a single, high efficiency solar cell that is very small, on the order of 1-centimeter square.
When you hear about a new world record for PV efficiency that exceeds 40%, it is generally this type of technology they are utilizing. CPV's "better mousetrap" uses less photovoltaic material (tiny, high efficiency cells), concentrates the sun and increases performance, hopefully enough to offset any additional costs.
2. Concentrating solar thermal (CST) technology uses mirrors to focus the sun's light on a heat capturing point, the heat from which can then be either used directly or converted to electricity. The three basic designs of CST are troughs, towers and dish-engine systems.
Troughs are set-up in large horizontal fields that contain long loops of piping (many kilometers for large installations). The pipes collect the 600+ degree (F) heat from light reflected off mirrors that concentrate the sunlight in a line on the pipes. Troughs have the longest proven operating history and the least number of unknowns for CSP technology project development.
Towers use a mirror field that is set-up around the tower. The mirrors focus sunlight on a heat receiver at the top that collects the heat and transfers it to piping inside the tower where is it circulated and used to make electricity. The design minimizes the field of piping to the vertical tower height to a few hundred meters and can reach temperatures in excess of 1000 degrees (F). While currently there are very few commercially operating tower installations, based on announcements, this technology may grow rapidly.
Dish-engine systems look like satellite dishes and focus light on a Sterling engine mounted on an arm in front of the mirrors. Each dish-engine is an autonomous generator—unlike the other CSP technologies that use a central power plant design—and utilizes a temperature and pressure difference to produce kinetic movement inside the engine, which is then converted to electricity.
An interesting development for troughs (and possibly towers in the future) is the interest on the part of utilities in "hybrid-solar power plants," which include the pairing or retrofitting of natural gas or coal power plants with the thermal input or boost from CSP.
The one thing that is common among the different kinds of concentrating solar power technologies is that unlike traditional photovoltaic panels, they need "direct normal" solar radiation, i.e. sunlight that can cast a shadow. A certain percentage of solar radiation is made up of diffuse or scattered light, caused by clouds, humidity or particulates. Solar resource measurements are reported as either "direct" normal radiation (no diffuse light) or total radiation (diffuse + direct).
The southwest has the highest percentage of "direct normal" radiation of nearly anywhere in the world, making this one of the best regions for development of CSP. However, there is one CSP trough project in Florida—a hybrid CSP plant that will augment a natural gas plant—and a number of trough and tower projects in Spain. CSP will work in both areas, but performance will be commensurately reduced based on the direct normal radiation profiles.
The CSP industry is growing fast in Spain and the United States, and SEPA is tracking over 5,000 MW of new project announcements that are slated for development over the next five years. Not all of them will be built—permitting, financing, technology and other factors need to fall into place first—but the industry is poised for rapid growth regardless of any individual project's outcome.
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HelioDynamics Commissions Solar Concentrator Project In California
SI Staff, Tuesday 12 May 2009 - 10:21:36
International energy integrator EnergyMixx AG says that its wholly owned subsidiary, HelioDynamics, has successfully completed commissioning of its latest solar project.
The project, which incorporates HelioDynamic's linear Fresnel solar concentration technology, provides energy for air conditioning on the Southern California Gas Co. Energy Resource Center located in Downey, Calif. The system is part of a comparative program to use heat generated by the sun to power an absorption chiller that feeds cold water to the air conditioning loop.
The HelioDynamics solar concentrator is available for the generation of industrial-grade heat at temperatures in excess of 185 degrees C. It uses EnergyMixx-developed Technology, employing simple flat-glass mirrors held within a lightweight, low-cost but robust aluminum frame.
SOURCE: EnergyMixx AG
this content item is from Solar Industry
( http://www.solarindustrymag.com/e107_plugins/content/content.php?content.3113 )
Sunday, May 10, 2009
How to Make the Green Revolution Work
The best way to go green: carbon taxes, cap-and-trade -- and white paint.
IF THE NATION IS GOING GREEN, THEN CONGRESS AND THE administration should go for a jolting, life-altering transition in a logical, cost-effective manner. However, the evidence so far is that logic will play second fiddle to fashion.
Scientist-businessman Arnold Leitner points to tax subsidies for hybrid cars and photovoltaic systems as being especially inefficient applications of tax dollars to alter consumer behavior.
"Right now, the entire environmental discussion is driven by the affluent do-gooder who want to save the planet," he says. "The result is a complete misallocation of our tax money."
Government programs supporting weatherization and white paint make sense, he says; they'd provide more bang for the buck in helping utilities meet peak demand than would support for expensive, relatively inefficient photovoltaic systems.
And funding light-rail systems powered by clean energy is also going to have greater impact than giving tax breaks to people who buy hybrids, which still require gasoline.
Leitner, who was reared in Germany, holds a doctoral degree in physics from the University of Colorado and runs a highly innovative alternative-energy outfit called SkyFuel.
LEITNER ASSERTS THAT APPLYING WHITE paint to the roofs of commercial buildings in warm and sunny places like Los Angeles would cut their air-conditioning costs by 15% to 20%.
"We now consume twice as much energy in this country as we have to, because we are wasteful and not smart," he says. He also recommends widespread use of roof-top solar hot water systems to significantly cut electric demand.
If it sounds as though Leitner has an axe to grind against photovoltaics (PV), he does and he doesn't.
He spent his early years as a physicist trying to develop PV film -- until government funding for the program was cut. He went on to research superconductors, elements that conduct electricity with little resistance. Now his company, based in New Mexico, may eventually go public; it competes against the PV industry for business and tax dollars.
Leitner is now hawking a technology called parabolic-trough solar collection. The trough system generates electric power by using highly reflective, mirrorlike polymer-based film to concentrate sunlight and heat a conducting fluid above 700 degrees Fahrenheit. The fluid, in turn, makes the steam that drives a plant's generators. Enough of that superheated water can be stored by a utility in an insulated container the size of an oil tank to produce electricity 24/7. By contrast, PV converts sunlight into power and has more limited storage capacity, so it is used in smaller applications.
Like photovoltaic power and other forms of green energy, Leitner's industry could not exist without government subsidies such as tax breaks and research credits. (He says that trough systems require a subsidy of 50 cents per kilowatt, versus $3 per kilowatt for PV). It is impossible in today's marketplace for renewable energy to compete against coal, as long as the cost for putting emissions into the atmosphere is free, Leitner adds.
SO HOW DOES THE GOVERNMENT GET its citizens to go green?
"If you want to change behavior, then you only get there when it hurts," he says. This means setting a floor price for carbon -- a base cost of doing business that shows the real cost of using carbon in the various things we do. The tax might have to be high enough to raise the cost of a barrel of oil back over $150. Last time oil hit that mark, gasoline shot up to $4-a-gallon (or higher in many regions) and commuters abandoned their cars for public transportation.
Leitner also says the government must avoid establishing a "renewable-energy portfolio" dictating the percent of power than must come from various sources like solar and wind. "Let the market respond to the price signal," he urges Congress.
Leitner favors a regime that would have a cap-and-trade system for registered, fixed-place emitters and a simple carbon tax for the rest of us.
The public will not stand for such a tax if it does not perceive that it's getting something in return. He suggests using the proceeds to fund "sacred programs" like benefits for veterans, something no future politician in his right mind would consider rolling back.
Leitner sees a payoff for our children and grandchildren. Although the start-up costs for solar-trough and wind power are high, longer term, the cost of producing energy in these systems is practically free, he says. He points to the big dams built by the U.S. in the 1930s. They were paid off long ago, but are still operating and producing power at nearly zero cost.
E-mail: jim.mctague@barrons.com
Wednesday, May 6, 2009
Hybrid Air-Conditioning System Reduces Energy Use 60%
The DuHybrid system operates in one of two modes. The renewable energy mode is the default mode of operation. Based on the application, in this mode the unit can generate over 20 TR (tons of refrigeration) of cooling and dehumidification using renewable energy sources such as solar thermal and geothermal water. In the electric mode of operation an embedded compressor is activated to enable efficient cooling and dehumidification by utilizing the waste heat of the compressor as an internal energy source. The DuHybrid system can be supplied in one of the three configurations, 1400CFM, 2400CFM and 3400CFM, that cover a broad range of commercial and industrial needs for air conditioning and dehumidification.
Additional benefits of the DuHybrid system include the ability to control humidity and temperature independently (variable sensible heat ratio). This guarantees that the required conditions, both temperature and humidity, are achieved in the most energy efficient way. The DuHybrid's liquid desiccant cooling process eliminates 91% of the bacteria in the air in a single pass and removes over 80% of all particles larger than five microns including allergens such as pollen, dust and other airborne particles. These air scrubbing qualities are inherent to all of DuCool's cooling and dehumidification systems.
About DuCool
DuCool's systems cool, heat, dehumidify, disinfect and clean the air while providing independent control of temperature and humidity. DuCool's solutions are powered by renewable energy sources such as solar thermal panels, geothermal water or available low grade waste heat, providing considerable savings to commercial and industrial users. DuCool systems utilize a patented liquid desiccant process for dehumidification and air conditioning that is considerably more efficient and effective than other air conditioning and /dehumidifying solutions. DuCool systems can be configured as a standalone solution or they can be coupled with existing conventional systems to provide a superior energy saving solution.
Starfish reinvests in solar company
Joins managers to set up equity funding facility
By Alice Uribe
Thu 07 May 2009
Starfish has joined with five other managers to establish an equity funding facility for Ausra.
Venture capital manager Starfish Ventures has reinvested in California-based solar thermal energy company Ausra.
The Melbourne-headquartered manager is part of a group of five that has ploughed $25.5 million into an equity funding facility for the company.
Other members of the group are Al Gore-founded Generation Investment Management, Ausra founding investors Khosla Ventures and Kleiner Perkins Caufield & Byers, and Kern Partners.
Funds from the equity facility will be available to Ausra for acceleration of the company's solar thermal energy equipment supply business.
Ausra said the group had committed the funds to support global expansion opportunities for existing power generation and industrial steam applications.
Starfish Ventures has had a number of institutional investors, including Westscheme and MTAA Super.Sunday, May 3, 2009
The Secret to Low-Water-Use, High-Efficiency Concentrating Solar Power
Many readers have expressed interest in learning more about the water consumption of concentrating solar power and how measures to reduce it might impact system efficiency and cost. After my recent CSP post, "World's largest solar power plants with thermal storage to be built in Arizona," Michael Hogan wrote in the comments (here) about a low-water-consuming cooling system he had experience with. I asked Hogan, a long-time power industry executive and currently the Power Programme Director for the European Climate Foundation (bio here), to write a longer piece for Climate Progress. Here is what he put together, with links and figures (click to enlarge).
EXECUTIVE SUMMARY: If concentrating solar power ("CSP") is a core climate solution, indirect dry cooling systems (also known as "Heller" systems) will be a crucial enabling technology, since large-scale CSP will be located in desert regions. US power companies have long favored direct dry cooling systems for fossil plants, probably because of the visual impact of Heller systems. But Heller systems have long experience in certain regions and will probably play an important role in the success of large-scale CSP. This is due to their higher efficiency, smaller footprints, quieter operation, lower maintenance, higher availability, and more flexible site layout. Heller systems can reduce water consumption in a CSP plant by 97% with minimal performance impact. The height of the cooling towers should be less of an issue in remote desert locations, especially since the central tower in power tower facilities will be of comparable height.
Concentrating solar thermal power plants ("CSP") have been identified a number of times in Climate Progress as a core climate solution due to their almost unique potential to replace coal as the dominant supplier of baseload and/or firm dispatchable capacity to the world's power grids. It is said that CSP could represent 3 of the 12-14 wedges in the 450ppm solution –- 20-25% of global mitigation potential. I concur wholeheartedly with that view, and I applaud CP for its efforts to educate readers on the singular challenges of eliminating coal-fired power production at scale. But if CSP is a core climate solution, dry cooling technologies, and in particular Heller systems, will be a crucial enabler (see note at the end regarding the status of the name "Heller" system).
One of the concerns often cited about CSP is water consumption, particularly because the technology's reliance on direct normal insolation means that it is most economically located in desert regions. Because most CSP systems rely on Rankine cycle steam turbine-generators to produce electricity, they face the same requirements as fossil-fired power plants for condensing large volumes of saturated steam back into boiler feedwater. (Parabolic dish systems use Stirling or Brayton engines to produce useful energy, each of which has its own advantages and disadvantages) Where an abundant and cheap supply of water is available, the most efficient way to accomplish this is by evaporation (or "wet cooling"), which is what produces the large plume of water vapor one often sees rising from power stations. Convective cooling using ambient air ("dry cooling") requires higher capital costs and can reduce plant performance, and thus planners of fossil plants have sought to locate them close to adequate supplies of cooling water whenever possible.
In the desert areas where CSP will thrive, the consumption of large amounts of water by conventional wet cooling systems is clearly unsustainable. Dry cooling alternatives will be required, and CSP will have to demonstrate its commercial viability despite the capital cost and performance penalties this will entail. Fortunately this is an eminently manageable problem.
[Acronyms: "LEC" = levelized electricity cost; "O&M" = operation & maintenance]
Deutsches Zentrum fur Luft- und Raumfahrt e.V. ("DLR"), a German government research agency, presented a study in 2007 comparing a particular dry cooling technology, the Heller system, with wet cooling for CSP plants in Spain and in the California desert (see figures above). Water consumption was reduced by 97%, and the performance impact was quite minimal. Indeed the impact on performance in the higher desert temperatures of California was overwhelmed by the benefits of better annual insolation. They also noted that the potentially negative impact of high daytime temperatures is mitigated by the use of thermal storage, which uses energy collected during peak daytime insolation to produce electricity when temperatures are considerably lower. One interesting aspect of the DLR study was their focus on Heller systems over more familiar (at least in the US) direct dry cooling systems, and that is worth a closer examination.
Two basic types of dry cooling systems have long been employed where necessary -– "direct" air cooling (usually called an "air-cooled condenser" or "ACC") and "indirect" air cooling (often referred to as the "Heller system", after Laszlo Heller, the Hungarian thermodynamics professor who pioneered this approach in the 1950s). In ACC systems, the saturated steam from the steam turbine exhaust is carried directly to a very large array of A-framed fin-tube bundles, where large mechanical fans force air over the tubes, convectively condensing the steam.
ACC system
In Heller systems, the steam is condensed by spraying water directly into the exhaust flow in a ratio of about 50:1 (called "direct contact jet condensing"), creating a large volume of warm water, some of which is pumped back to the boiler as the working fluid and the rest of which is pumped to bundles of tubes arrayed at the base of a natural-draft hyperbolic cooling tower. The warm water circulating around the base of the tower and the cooler air at the top of the tower, combined with the tower's hyperbolic shape, stimulate a powerful updraft that draws ambient air over the tube bundles, thereby convectively cooling the water before it is returned to the condenser. Both are closed systems.
Heller system [Acronyms: "CW" = cooling water; "DC" = direct contact]
While the Heller system has been widely used elsewhere, there are none in the US. This is probably because the much lower auxiliary power requirements of Heller systems come with the visual impact of a large hyperbolic cooling tower (typically 150m high and 120m in base diameter), often a difficult sell given that most fossil power stations are located in the vicinity of the populated demand centers they're intended to serve. The auxiliary power required to run an ACC system is roughly twice the power required run a Heller system, and the Heller system is considerably quieter, but these have apparently been considered prices worth paying for the lower profile (a typical ACC system can be 40m high), particularly when it was cheap coal-fired power. Simple lack of familiarity could be another factor in the hidebound world of US power utilities.
The Electric Power Research Institute has kicked off a comparative study of indirect dry cooling (due to be completed in mid 2010), on the theory that it is the most economic dry cooling solution for large-scale thermal applications. The prospect of large amounts of CSP being built in the world's deserts calls for a reconsideration of the relative merits of these two approaches, since it would require dry cooling to be deployed in a different application and to a far larger extent than has ever been the case.
Three Bechtel engineers published a paper in 2005 (Digital Object Identifier reference DOI:10.1115/1.1839924) (originally presented at an American Society of Mechanical Engineers conference in 2002) that compared cooling technologies for combined-cycle gas power plants. They cited the following comparison of installed costs for various cooling systems, including ACC and Heller.
[Acronyms: "WSAC" – wet-surface air condenser]
They also note that the footprint of an ACC system is larger than that required for a Heller system, though specific data is not offered. Overall system efficiency of a Heller system is in the range of 2% better than an ACC system. That performance improvement meant one thing in a fossil power plant in the bad old days of cheap dirty power, but when it means 2% less land area covered by solar collectors, and lower auxiliary consumption of much more costly power, it takes on a much greater significance. The same sources note that since the Heller systems are mechanically far simpler than ACC systems, maintenance is much less of an issue and system availability is significantly greater. In the remote areas where these plants will be located, and given the large land areas over which they will spread, these are far more significant considerations than they were for compact fossil power plants located close to the populations they served. Another factor noted in these sources is that an ACC must be located next to the steam turbine it serves, because of the cost of transporting saturated steam over any distance, whereas the Heller system has much more flexibility in where the cooling tower is located. This will be much more important to CSP, where one can envision clusters of power tower complexes in a given area each with its own steam turbine, than it was with fossil plants. And finally, the feature that most worked against Heller systems in US fossil plant applications – visual impact – should be far less of an issue in remote desert sites, especially with solar power tower complexes where the central towers will likely be of similar height.
I should note that as a senior executive of the private power company InterGen in the late 1990s I oversaw the deployment of a Heller system on our 2,400 MW gas-fired combined cycle plant in Adapazari, Turkey (see below), which is still the world's largest installation of an indirect dry cooling system and continues to work extremely well. I trace my enthusiasm for the technology to that personal experience.
One final note on the term "Heller" system. A German engineering company, GEA, appears to own the trademark rights to the name "Heller", which they acquired when the bought EGI, the Hungarian company that commercialized indirect dry cooling systems. Indirect dry cooling is a generic technical solution that is often referred to as "the Heller system". I have no affiliation with GEA.
This piece originally appeared in Climate Progress.
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I am happy to see it pointed out that large amounts of water are not needed for solar power. Thanks.
There seem to be two design decisions here: whether to use direct or indirect condensation, and whether to use a cooling tower or forced cooling. Only 2 of the possible 4 combinations are discussed. Lets say I've decided I will use a cooling tower. What advantage is there to using the Heller system over placing a direct condensing system in my tower? (Other than less steam piping, I get that).
I see one advantage to direct: The steam is hotter than the water will be in the Heller system, so the fluid to air heat exchanger will be smaller, and hence cheaper.
Posted by: Bart Hibbs on May 1, 2009 8:52 AM