They do it with Mirrors: Concentrating Solar Power

Note 5/3/09 Some more recent CSP articles are here.

I’ve just spent some time reviewing a pile of reports on concentrating solar power (CSP) technologies for Ratepayers United Colorado (RUC), so here is a summary of the various types.

 

Technology descriptions

        Concentrating Photovoltaic

o       This technology uses mirrors or lenses to focus sunlight on high-efficiency photovoltaic chips.  The extra sunlight makes it worth the expense of making a more efficient higher complexity chip because each chip can convert more sunlight to electricity, with conversion efficiencies often twice as high as the efficiencies of conventional soar panels.  This also has the advantage of saving silicon (which is in short supply) for making chips.  Problems are that they do not work as well as conventional panels in diffuse light through clouds (because the light cannot be focused) so they are only appropriate for areas with very little cloud cover, and the extra light heats the chips more, which lowers their efficiency, and so may require some sort of additional cooling loop.

o       Article links:

o       http://thefraserdomain.typepad.com/energy/2006/03/concentrix_conc.html

o       http://thefraserdomain.typepad.com/energy/2005/11/stellaris_conce.html

        Parabolic trough

o       The oldest CSP technology, parabolic trough plants, known as SEGS 1 through 9, have been operating reliably in theParabolic solar trough technology  -  such as this SEGS plant - will be reborn in Red Rocks, California.
California and Nevada deserts since the 1970.  Parabolic trough plants work by focusing sunlight on pipes by means of parabolic mirrors.  These pipes contain a working fluid (several have been used, from water and superheated steam to molten nitrate salts.)

o       Parabolic trough technology is currently experiencing a revival, with several new plants being built.  The using of Organinc Rankine Cycle generators allows solar trough plants as small as 1 MW to be built (such as the new Saguaro plant north of
Tucson, AZ.

o       Parabolic trough technology allows energy to be stored as heat, which is much less expensive than storing electricity.  This allows the energy from these plants to be available at times of peak demand, making the electricity much more valuable.

o       Steve Raabe recently wrote an article for the Denver Post providing a good overview of the prospects of this technology in
Colorado.  The only point that he missed is the potential for hybridization with existing coal and gas plants.  By preheating steam for an existing fossil fuel fired turbine, CSP can make an old power plant operate much more efficiently.  Arnold Leitner of SkyFuel (
www.skyfuel.com) tells me “Our preliminary engineering estimates, satellite imagery of the locations and solar data show that SkyFuel could supply 50-100 MW-electric solar steam to the Comanche power plants generating an estimated 65,700-131,400 MWh of pure solar power at the facility via the existing steam turbine. SkyFuel could deliver this solar-generated steam to the power plant at an effective fuel cost commensurate to the fuel cost of burning natural gas at a modern combined cycle power plant at fuel price of 7-8 cents/mmBtu. In other words, through a FuelSaverTM at a coal-fired power plant SkyFuel could provide solar energy at the price of natural gas generation.”

o       Considering that solar power is available during peak demand, gas ifered generation is the appropriate cost comparison (as opposed to wind power, which does not deserve (or need) a price premium due to its unpredictable timing.

o       A variant on this called Concentrating Linear Fresnel Reflector (CLFR) uses many thin mirror strips instead of parabolic

troughs to concentrate sunlight from a large field onto just two tubes of working fluid.  This has the advantage that flat mirrors are much cheaper to produce that parabolic mirrors, and also allows for a greater density of reflectors in the array, allowing more of the sunlight to be used.

        Power Tower

o       Power Tower technology is similar to solar trough technology in that it uses mirrors to concentrate sunlight on a working fluid which is then used to superheat steam to run a turbine.  The difference is that the mirrors concentrate all the sunlight onto a single receiver at the top of a tower.  This allows for higher temperatures, but leads to engineering problems because of the high temperature at the receiver.

o       Lower price per watt is theoretically possible compared to trough technology because of the higher temperatures.

o       So far, only two pilot plants have been built and operated, called Solar One and Solar Two (actually the same facility as Solar One, but converted to use nitrate salts as the working fluid rather than superheated steam).    Both Solar One and Two incorporated thermal energy storage.  Due to the success in demonstrating the technology of Solar Two, a commercial 15MW plant Solar Tres is in the planning stations.  This station will incorporate enough thermal storage in molten salt tanks for 24h operation.

        Solar Chimney

o       A Solar chimney consists of a large greenhouse (multiple square miles of area covered by a transparent roof) which is sloped gently up to a central hollow tower or chimney.  The sun heats the air in the greenhouse which then rises up the chimney driving an air turbine (similar to the hydroelectric turbines used to generate power at dams) in the chimney as it rises.  Water filled tubes on the floor of the greenhouse serve as heat storage which allows the chimney to operate even at night and on cloudy days.  The amount of water in the tubes can be changed to alter the profile of power production and match it closely to the power demand the chimney serves.

o       The edges of the greenhouse can actually be used for agribusiness to grow plants, so not all the space taken up is solely devoted to electric production. 

o       The beauty of solar chimneys is that they are extremely low tech, and can be built without heavy equipment using simple materials.  The only exception to this is the turbine, and even that is much less complex than turbines used to generate power from wind, because the wind in a solar chimney is much more regular than naturally occurring winds and storms that wind turbines have to deal with. 

o       The first solar chimney was built in
Manzanares, Spain and ran continuously for 32 months in the late 1980s with 95% availability (considerably better than most coal and nuclear plants.)   See a video tour of this chimney I ran across on EcoGeek.

o       A 200MW chimney is planned by EnviroMission of Melbourne Austrailia for the Austrailian Outback.

o       It may be possible to build solar chimneys on south-facing slopes or simply as an extra layer of glazing on tall buildings with a turbine at the top which would make them even cheaper by avoiding the necessity of building the tall chimney (my idea).

 

        Dish Stirling

o       A Dish Stirling system is a parabolic mirror which focuses heat directly on a Stirling engine, a simple closed-cycle engine which operates simply using any heat source.  Sometimes hybridized with a fossil fuel source to provide heat when the sun is not shining. 

o       Dish
Sterling systems have the advantage of small size and scalability, because each individual mirror-engine system produces only around 25kW, but many can by linked together.

o       Because the suns rays are focused directly on the engine, there is little opportunity for thermal storage, a great advantage of several other thermal concentrating technologies.

o       Stirling Energy Systems currently has a few demonstration systems in operation.  They have signed purchase agreements with two
California utilities to build a total of around 1 GW of electric generation, but both projects are still in early testing phases.

o       According to Sandia National labs, this is the most efficient technology for converting sunlight into electricity.

CSP Technology comparisons

Technology Scale Levelized cost per MWh Pros/Cons Complexity/ deployment

Concentrating PV

Any

$15-$20

No storage option; does not work well on cloudy days

High.  Beginning to be deployed in last couple years.

Dish
Sterling

25 kW per dish

Unknown

High efficiency, modular.  No thermal storage.

Just beginning to be deploy

Parabolic Trough

Most: >50 MW for economies of scale;

Organic Rankine Cycle 1MW+

$8-$18 current

$6 potential

Can hybridize with existing fossil plants.

Storage, well understood technology, needs water for efficient cooling.

Plants operating consistently for 30 years in CA.

Solar Tower

>30 MW

$18+ current,

$5 potential,

can hybridize with existing fossil plants.

Storage.  Potentially cheaper than solar trough. Needs water for efficient cooling.

2 pilot plants with operational history.  First commercial plant now operational.

Solar Chimney

100-200MW

Not yet known.

Baseload power, low maintenance.

Low complexity, great potential for 3rd world.

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31 Comments

  1. Leslie Glustrom said

    Great summary Tom–Thanks!

    I especially like the idea of doing a solar greenhouse with turbine in combination with tall buildings.

    Whether that particular idea works or not, it is part of what I’ve long said about unleashing our ingenuity. It is going to be such fun once we get going on all of this for real!

    Thanks again. It is great to have you working on clean energy for the citizens of Colorado–and the world! Leslie

    P.S. Check out the trec-uk website….:) and then you might want to get hooked up with Gerry who runs that site. He and I exchanged e-mails earlier this week. Good things are happening!

  2. anthea said

    what do people use at night?

  3. Tom said

    The great thing about CSP is that it is a lot easier t store heat than electricity. The heat can variously be stored in large insulated tanks of water, molten salt, or oil. The heat stored that way can be used to generate electricity at night or on cloudy days.

  4. peter kyte said

    I’ve become interested in concentrated solar power… do you feel it will be private sector or government led and are there any avenues to invest in the stock market for CSP???

  5. Tom said

    Government will have to get the policies right to get these projects started, but the investments will be made by privately owned companies. Unfortunately, there are not American listed stocks that are deeply involved in this field, but there are a few publicly traded compaines in world markets.

    Acciona: a Spanish firm which was part of the consortium that build Nevada Solar One
    Iberdrola: A spanish utility that has a CSP arm, and is moving into the US.
    Enviromission: An Australian company that is construction solar chimneys.

    In the US markets, you can buy FPL (Florida Power and Light): A US utility that owns the majority of the SEGS built in California nad Nevada in the 70′s and 80′s. It may be reasonable to presume that they have some interest in building more because they have experience running the existing CSP plants.

    Note: This is just a listing of the public companies I know of that are involved in CSP. The decision to or not to invest in any or all of these is your own. I cannot make a reccomendation without knowing your personal financial situation.

  6. Bonnici said

    I saw a solar power car in Colorado where can I find more information on them?
    TK: I just read an article about solar powering your Prius on EcoGeek.

  7. Fred Kirsch said

    I’m researching alternatives to RECs for Fort Collins’ “green energy” plan. Any investment opportunities in CSP for city dollars?

  8. Tom said

    Fred- as far as I know, there are no current plans on the drawing board for a CSP plant… but that might change very soon. The only recent plants built in the US are a small one in Arizona, and Nevada Solar One, both of which were built to help meet those states’ RPS requirements, so I doubt there are SRECs available from them.

    I’ll to pass your contact information on to other people who who may know anyone trying to get a CSP project started in Colorado.

  9. [...] Linear Fresnel Reflector (CLFR) developer Ausra has been keeping long-underappreciated Concentrating Solar Power (CSP) technology in the news recently.  I consider this great news, because the potential for [...]

  10. [...] The only exception to this broad trend is the selection of "Parabolic Dish Engine" (which I usually refer to as Dish-Stirling) and the emphasis of large scale Photovoltaic over small scale residential solar photovoltaic (most [...]

  11. C J vd Merwe said

    I am farmer of South Africa developing an irrigation farm and enjoys 345 days without any clouds per year. Can CSP be an option?

  12. Tom said

    CJ: South africa has a good solar resource for CSP, especially in the NE of the country.

    Click here for a map.

    So there is potential. Most projects tend to be very large, however, to acheive economies of scale.

  13. [...] exciting news has been emerging about solar-thermal. It’s been demonstrated as reliable for over twenty years, and new plants are coming online, or being planned, across the world. Energy is not the only [...]

  14. George said

    Anybody know of any CSP technology for individuals i.e for the cottage, campers etc?

  15. Solar Dave said

    I went by the largest PV planet in the US in Alamosa Colorado (I took some video and put it on my site) and I scratched my head an thought why they didn’t use concentrated solar instead.

  16. Tom said

    Solar Dave:
    I believe they chose not to use CSP for 2 reasons: the site is only 8MW, and CSP works best at over 15 MW for solar towers, and 200 MW for parabolic trough. The other reason was that the site has limited water, which means that the turbine would need air colling, which lowers the efficiency.

  17. Caferacer said

    There is a small private company in Nevada doing research on small scale csp. They are building a prototype this fall.

  18. [...] exciting news has been emerging about solar-thermal. It’s been demonstrated as reliable for over twenty years, and new plants are coming online, or being planned, across the world. Energy is not the only [...]

  19. Linn Gill said

    I see everyone is still chasing the sun , Well if someone would ask nicely I would show them an easier and cheaper way to get the same or better results. I wount sell the cow for beans but if somone wants to see how to produce power from sun light even in the dark give me a e-mail @ TAGz3339 yohh

  20. byezz said

    anybody could give some info about difference between parabolic dish,dish sterling and parabolic trough?i’m student interested in green tech-solar powered electrical system..tq

  21. IXLNXS said

    Using the principles of reflective light and heat you can easily build water treament plants that would not only produce clean drinking water but also electricity. All the parts already exist in differing mechanisms and just need to be combined to begin distilling seawater for a multitued of purposes.

  22. reza said

    dear
    I want completly information about this tecnology and money and capital for buy 20 Mwat of this system for instalation near a ready powerhouse by gas fuel .
    I want completly information about money and capital for buy a gas turbine sysytem by 20Mwat power

    tancks alot

  23. Dale Jamer said

    Great Post this will help keep up the good work.

  24. [...] They do it with Mirrors: Concentrating Solar Power « Clean Energy … – Note 5/3/09 Some more recent CSP articles are here. I’ve just spent some time reviewing a pile of reports on concentrating solar power (CSP) technologies for Ratepayers United Colorado (RUC), so here is a summary of the various types. o        This technology uses mirrors or lenses to focus sunlight on high-efficiency photovoltaic chips. [...]

  25. [...] renewable energy advocates (myself included) have long seen CSP as core to the decarbonization of the electric grid.  That’s [...]

  26. [...] renewable energy advocates (myself included) have long seen CSP as core to the decarbonization of the electric grid.  That’s [...]

  27. [...] renewable energy advocates (myself included) have long seen CSP as core to the decarbonization of the electric grid.  That’s because CSP [...]

  28. jack said

    Hello , my name is jagjit hans. I would like to enquire about the price of one dish stirling. I am interested in buying one dish and taking it to India to start an buisness.Thank you

    Sincerly,
    Jagjit Hans
    717-395-3956

  29. [...] since I first started writing about investing in clean energy, I’ve been fascinated by Concentrating Solar Thermal Power (CSP.)  CSP held the promise of much cheaper energy than was then available from photovoltiac (PV) [...]

  30. [...] before I started writing about investing in clean energy in 2006, I’ve been fascinated by Concentrating Solar Thermal Power (CSP.)  CSP held the promise of much cheaper energy than was then available from photovoltiac (PV) [...]

  31. [...] before I started writing about investing in clean energy in 2006, I've been fascinated by Concentrating Solar Thermal Power (CSP.) CSP held the promise of much cheaper energy than was then available from photovoltiac (PV) solar, [...]

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