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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 electric power (CSP).
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 power (CSP) 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 CSP 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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1. Concentrating Solar Thermal permanently destroys roughly 10 acres/mW of land; and
2. uses rougly 90,000 gallons/year/MW of scarce desert groundwater to rinse mirrors; and
3. production drops precipitously in hot climates, when power is needed most, so In order to be cost-effective, it requires BILLIONS more gallons of non-existent desert groundwater to water-cool. air cooled plants are much more expensive and much less productive;
so, actually, the desert Southwest - a highly effective carbon sink when left intact - is a LOUSY place to put these plants. It is only Big Energy propagandists and lobbyists who are rushing to destroy millions of acres of intact ecosystem to re-centralize and re-monopolize our energy supply who think of it as anything other than wasteful, GHG spewing, ecosystem slaughter.
The rest of us support point of use solutions like efficiency gains and rooftop solar, which would be plenty to power our nation over twice over, on existing rooftops and in-city brownfields. We are having our planet, our open spaces, our water table and our economy destroyed by Big Energy with these crappy projects and the greenwashing is disgusting.
Big Energy is the PROBLEM, not the solution. Look to yourself, your friends, and neighbors for the real solutions.
Higher efficiency means less land needed per mW.
Check out: http://www.tesserasolar.com/north-america/award-winner.htm
Am developing a revised version for water heating, may be able to combine with PV or make a PV version only. Interested parties please look at http://www.grunweb.org.uk for contact info
Roofing over open air car parks eg at shopping malls, would seem to be good sites for PV ? Could collect rainwater too.
Solar thermal is available to everyone at less than "bankster boyz bailout" prices. Heating homes, businesses, and institutions and their hot water is easily accomplished without increasing the electricity infrastructure. Saving more than half of their support outlay is the result. AND it is not purchased power. You make it, pollution free and cost free right at home. It only requires paying for a support of a lifetimes supply of heating energy up front, something that could be done for less than the cost of the financial bailout, which we will pay for again and again.
Efficiency, demand management and wise use are the answer. We are the problem.
If only "big energy" would quintuple rates and reduce service reliability then we could not blame them for standing in the way of the individual power producer/consumer. That would open the door to those who can do it faster,better,cheaper,whatever. Then the playing field would be equal.
Steven
Cloud cover over the Sahara desert is not likely to be an issue anytime soon, and similar statements could be made about many deserts. One would think that making mirrors for focusing is cheaper than making high-efficiency PV cells so CSP should be cost competitive with PV and will hopefully be subject to better economies of scale. Additionally, the option for thermal storage allows for a degree of load balancing that PV does not possess.
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