Solar Thermal

I wish I could tell you that the following story happened when I was a kid, but it actually happened just a few years ago. We were back home at the family farm in Oklahoma, and my Dad had a magnifying glass that he used for reading. I liked playing with magnifying glasses as a kid, so I took my (then) 8-year-old son outside and started showing him how it worked. There was a pine tree stump in the yard, and we rigged the glass up in stationary fashion so that the sun burned a black line across the stump as it moved across the sky. We both thought this was very cool, as it indirectly showed the sun’s movement across the sky, and it also showed just how powerful the sun can be.

We did this off and on for a couple of days. One day, I heard my Mom ask “Is something burning?” Oklahoma was in the midst of a drought, and I walked outside to see the pine stump on fire, and the grass in the yard burning. The magnifying glass was a melted mass on top of the pine stump. After putting the fire out, I thought “Wow, a few large concentrating mirrors could provide a lot of energy in a small space.”

This is of course one of the applications of solar thermal energy. A number of companies are in the process of building solar thermal plants, including Nevada Solar One with their 64 megawatt plant in Nevada. While this will be the largest solar thermal plant to be constructed in over 10 years, the largest solar thermal plant in the world is a 350 megawatt plant in California’s Mojave Desert, run by Solel from Israel. Solel is also building the Mojave Solar Park, which is scheduled for completion in 2011, and will supply 553 megawatts of electricity to the citizens of California. (I presume that the 553 megawatts is in addition to the 350 megawatts of presently installed capacity).

As far as costs, Solel’s FAQ states:

Even without pricing cost externalities, the cost of solar thermal power is going down. Currently, the cost of solar thermal produced energy can be close to 12 cents (US) per k/Wh. However, many economists and investors predict that this price will continuously drop over the next ten years with increased installed capacity, to 6 cents per kW/h, as a result of technological improvements, economies of scale and volume production.

Other applications of solar thermal include solar water heaters and solar cookers. Both have great appeal, especially in tropical locations where affordable energy is often in short supply.

Additional information may be found at the EIA’s page on solar thermal.

31 thoughts on “Solar Thermal”

  1. Dave Mathews continues to attempt to pollute every thread in this blog. I have had to delete 2 off-topic rants in this thread already. As I said, I will enable comment moderation if necessary. Note that if I do, his comments will be the only ones removed (and I know which ones belong to him).

    Dave, in case you didn’t get the message, you wore out your welcome with your charges of lies, racism, and just general slander. As I said, get your own blog and you can rant to your heart’s content. But this blog is for energy discussions. It is not a forum for a mentally disturbed person’s rants.

    I gave you many chances – even after you called me a liar, after you made all kinds of false accusations. But you showed that you could not even demonstrate the minimum level of civility. So at this point, nothing you say is welcome here. Not even, “It’s a nice day.” Notice that I have other critics, and I haven’t had to take this action with anyone else. Why? Because while they may disagree, they don’t resort to childish, off-topic rants. (I can’t believe that you don’t understand why TOD would ban you).

    Now, instead of obsessing over me, why don’t you go and enjoy life yourself? Get away from that computer for a while. It’s clear from your long diatribes here and at Kunstler’s blog, you haven’t been away from it much lately.

  2. These things are very impressive. I think they about 25% efficiency so that would make the square from your solar experiment even smaller.

    It’s funny you mention the episode about the magnifying glass. A few weeks ago I got one of those magnifying mirrors to show my son. They are a little haredr to control than a magnifying glass though.

    I just finished reading the Methanol Economy. How cheap would electricity have to be to produce methanol from hydrogen and CO2.

    I know people are always saying that electrolysis is inefficient, but wouldn’t it be possible to utilze a lot of the waste heat?

  3. solar window heater

    nice example of an easy to build solar air heater. It’s completely passive and this diagram is missing only one thing which is a vent for summertime use. of course, one could remove the heater from the window every spring but an external vent would enable solar driven air movement by sucking in air from the house, heating it, and venting the hot air up and out. Although I will say, nothing beats an air conditioner for keeping you cool enough for your brain to function

  4. Solar thermal at 6 cents per kW/h would be big news for the southwest.

    Though I assume that wind is still considered the better ‘proven’ technology for the soutwest?

    I believe wind MW are being added faster.

  5. 12 cents / kwh is terrific if true. I’m having trouble squaring that with some recent articles in the SF paper that gave numbers in the 20-25 cent range for a solar thermal project (might even have been the same one).

  6. odograph: very nice solar products. Thanks for posting them. I do love the “tool Time” oven. It looks like it’s even big enough for a long pork on a stick. (Long pork: the other other white meat. Reduces population pressure and feeds the remaining hungry):-)

    I will admit that when they talked about hybrid barbecues in the caption, I wondered where they put the charcoal and why didn’t it smoke up the glass. 🙂

    — country mouse

  7. I’ve seen studies of the 354 MW Mojave setup showing 16 cents/kWh levelized cost, so 12 cents is not out of bounds for current technology. That said, I now lean away from solar thermal electricity and toward CPV.

    The cost of any highly concentrated system is mostly embedded in the mirrors, structures and tracking motors. The key parameter, therefore, is efficiency. It’s really hard to get solar heat engine efficiency above 30%, and current systems are closer to 20%. Photovoltaics, on the other hand, now exceed 40% with further improvements in sight. A system which delivers almost twice as much electricity from a given collection of mirrors and motors has an almost insurmountable advantage.

    Solar thermal still offers one unique possibility — cheap and efficient energy storage. Tanks can hold molten salts for dispatch during cloudy spells or even overnight. Current solar thermal systems don’t do this, but the Solar Two demo unit proved the principle. Over time this single feature could be enough to keep solar thermal in the mix.

    Of course solar thermal will probably always beat CPV for heat applications such as cooking, space heating, etc.

  8. The general drawback of concentrating solar thermal is that it requires direct sunlight. That means you need tracking equipment, which entails moving parts in addition to the working fluid, which will also entail moving parts. Furthermore, when you have a haze or clouds in the sky the incoming solar radiation becomes diffuse and normal concentrating optics are no longer effective. This serves to impose a minimum operating requirement (in terms of sunlight) before the systems will output significant power.

    There are ‘non-optical’ concentrating schemes out there. They are essentially very poor lenses that can accept light from many different angles. They cannot achieve a very high magnification however (~ x5) and hence cannot achieve the high temperatures that you want to drive the thermodynamic efficiency. As such are best suited for PV or solar hot water applications.

    Sorry to hear about your troll problems. You may want to look into replacing the default blogger commenting tool with something a little more robust. E.g. something that can do IP tracking and ban certain users. I don’t know much about the other commenting tools myself, however, so I cannot really be much of a help.

  9. Dave is still trolling, and I am still deleting.

    I am sorry, Dave. You appear to be an exceptionally slow learner. You lost any expectation of having me answer your questions. Had you remained moderately sane and civil, I would have engaged on any non-personal, energy-related topic you desired. As is, just consider it a lost opportunity to get your questions answered. You will have to take your man-crush elsewhere.

  10. You can get 40% efficient PV panels and you can get PV panels for $5 a watt. You just can’t do both at the same time. NASA doesn’t care how much their solar panels cost because they are going to spend ten grand a pound putting them into orbit.

    Issues with concentrated Solar power (CSP). CSP has to be tracked. CSP only uses direct sunlight. About half my photons are indirect light meaning they bounced around a few times before landing on my panels. PV lose half a percent of power per degree C. CSP heats up the panels. CSP panels don’t age as well because of higher current densities. Aren’t you better off just buying more silicon?

  11. You can get 40% efficient PV panels and you can get PV panels for $5 a watt. You just can’t do both at the same time.

    Say a tracking mirror system costs $1000 per square meter. At 500x you need a 4×5 cm PV cell to convert that light to electricity. A 15% silicon cell that size costs only a buck and outputs 150W. Your system cost is:

    ($1000 + $1)/150W = $6.67/W

    Now swap in an exotic triple-junction cell that costs a whopping $100, but achieves 40% efficiency. Your system cost:

    ($1000 + $100)/400W = $2.75/W

    A 100x INCREASE in solar cell cost delivers a 60% DECREASE in cost per watt. Note also the silicon CPV system is no cheaper than flat panel. Spending a lot on mirrors and motors to save (relatively) cheap silicon doesn’t really work. But triple-junction effectively leverages your tracking mirror investment to deliver a VERY cost competitive system.

    CPV makes cell cost irrelevant.
    Efficiency is all that matters.

  12. Say I spend $5 a watt for a 20% efficient PV panel from Sunpower. No tracker, no mirror, no moving parts.
    Total cost, $5 per watt.

    You spend $100 a watt for a 40% efficient PV panel from the University of Delaware. And $1000 for the tracker and mirrors. Half the incoming photons are indirect photons that won’t concentrate. Your magnifying glass heats your panel by 50 degrees C costing you 25% of your power. So you are converting into electricity 15% of the square meter of sunlight or 150 Watts.

    Your cost ($1000+$100)/150W=$7 per watt.

    Efficiency is all that matters. Concentrated solar power isn’t as efficient as a flat sheet of silicon.

  13. I ran across an interesting startup CPV company recently: SolFocus,

    The most interesting piece is the next generation “tile”:

    What’s shown in the photo is one of the 1st-gen mirrors, in which sits a 2nd-gen “tile” of stamped glass, 8mm thick. They think they can get 250+ W/m^2, with very small amounts of active material.

    It’s too early to know the real economics, but it at least looks interesting, a little like Therma-Cool Technologies. Reducing the size of active material is certainly good. Heating and indirect issues are still unclear to me.

    On a more generally applicable note, Charles Gay of Applied Materials gave a nice *engineering* talk over at SLAC in April about AM’s large & expanding investments in designing machinery for solar PV manufacturing, to complement AMAT’s businesses in semiconductor & flat-panel manufacturing gear. is a nice video.

    AMAT is a pretty serious/conservative company, so when they give straightforward engineering cost/volume trends (2X volume = -20% cost), I listen harder than to startup pitches for funding.

    Caveat: I don’t have any connection with SolFocus or AMAT; I do own some SPWR.

  14. 12 cents per kwh for heat is expensive. If you are paying 12 cents per kwh for electricity you can get heat out of it more efficiently (3x, 4x, maybe even 5x) using a heat pump.

    Electricity used directly for heat is one of the most expensive ways to heat. Therefore solar heat at a similar cost per kwh is expensive.

  15. I don’t have any idea what the real economics of CSP is. Unless you are putting something into orbit, the concept that cost doesn’t matter, only efficiency does, it ain’t necessarily so.

    There’s a big difference between being a homeowner and being a utility. I want something with no moving parts, no maintenance issues, and if a tracker breaks down it won’t set my roof on fire. A utility can have an electrician and a mechanical engineer on site 24 hours a day and if they can save a buck a watt on a 500 megawatt solar installation, that’s real money.

  16. Another point on solar heat: The economics depends heavily on where you are. A place with cold weather but lots of solar radiation is the best candidate. For example, the US high plains states such as the Dakotas are better candidates than New England because the Dakotas, even though they have very cold winters, have clearer skies and get much more insolation.

  17. The economics for rooftop solar depend heavily on how much do they want for a kilowatt and how big a rebate will they give you. Quality of sun is not as important an issue. Cold crisp blue skies are perfect. They use solar along with wind power at the south pole. 24 hours of sunlight a day during the antarctic summer, after which everybody goes home for the winter.

    Solar sucks in the northwest because in addition to 300 days of rain, they have cheap hydropower. I’m guessing solar will have trouble competing with wind in the Dakotas, but it isn’t my problem either. Anyone with an acre or more of land should think windmill first. They wanted 2.5 million dollars for an acre of raw unimproved land in silicon valley when I moved out. I don’t have an acre so I got rooftoop solar.

    My panels are producing more power than expected this year and I credit the southern california drought. I’ve never seen anyone mention it but ISTM that solar run countercyclical to hydroelectricity. Our hydro comes mainly from the Columbia River and Hoover Dam, so it can be pouring rain here and still not have a head of water at the turbines.

  18. Robert,

    RR’s article discusses CSP plants: large installations in sunny locations. I made two points:

    1) I now favor CPV over CSP due to new, high efficiency cells

    2) When it comes to CPV, expensive triple-junction beats cheap silicon

    You seem focused on residential rooftops in cloudy climates. That’s a completely different application from what RR’s article and my comments address. For the record, I agree CPV is a bad fit for rooftops in Seattle and Maine. Are we OK now?

    Getting back to CPV, Boeing SpectroLab has lots of info on their terrestrial concentrator cells. Today’s commercial cells are rated at 35% and deliver about 30% in the field. They cost twice what I thought — $10/cm2 in high volume. I’m sure they’d be a lot cheaper in a competitive market, but it’s still only 65 cents/watt.

    An outfit in Australia signed a deal with SpectroLab for a 154 MW CPV installation in NW Victoria. They claim a very impressive $2.30/W but it’ll be a couple years before we know if that’s real or hot air. I’ve seen studies showing $2/W-ish costs for other CPV designs, so I tend to think someone will do it.

  19. Solar thermal is great for utility-scale production in the desert.
    However, I’m not sure that it will improve the square-mile numbers for the solar thought experiment. While a single collector may get 20%+ efficiency, they tend to put a lot of space between these solar thermal collectors. I think it has to do with solar tracking and not wanting any collector to shade any other collector.

    According to their 553 MW solar thermal system will cover up to nine square miles”. That’s 553,000 KW per 23,300,000 square meters or 0.024 KW/m^2 or 2.4% efficiency over the entire area. Not terribly impressive, but desert land is cheap.

    anyone with an acre or more of land should think windmill first.

    I don’t have an acre, but I did think of windmill second, after solar. I found that where I am, we do not get enough wind to keep a electricity-generating wind turbine turning. Even if the wind could get the turbine turning, it would be nowhere near the rated power output of the wind turbine since power generated is proportional to the cube of the wind speed. If I got a Skystream 3.7 and had 24 mph winds I could get a nice 800 kWh/month, but where I am, I’d be lucky to get 8mph wind which would only yield 100 kWh/month. Not worth it.

    Think global, act local.

  20. Clee, I linked to a SpectroLab web page which has some other links to data sheets and such. I think the $10 price was in a FAQ. You’ll have to poke around some.

  21. I haven’t been able to find enough information on it to guess the cost per watt, but just on the technical design merits I have been very intrigued by the Sunflower CPV system in development at Energy Innovations.

    The advantages of their design is that the tracking mechanism is greatly simplified (only two motors, one for each axis) and the unit uses only a tiny bit of (presumably expensive, very high efficiency) PV collector material. They decided it was better than the concentrated solar thermal approach.

    But, based on the continuing developments in all forms of CSP, I think it’s probably too early to declare a winner. Let’s see what the playing field looks like when the Enviromission Solar Tower project is operational!


  22. Let’s see what the playing field looks like when the Enviromission Solar Tower project is operational!

    I have been intending to write about solar towers lately. I have been doing a lot of research into that area. Maybe when I get a bit more time.

  23. re: Sunflower
    Looks interesting, thanks; similar approach in some ways to SolFocus, but the low-profile Sunflower packaging would certainly fit my (flat) roof better, so I do hope they get to residential sometime.

    As usual, the our VCs are sprinkling money around in the hopes that at least one of these works big. There are still a lot of flat roofs here.

  24. Think wind first. If there ain’t no wind, put in solar. I don’t know where you live but I’m guessing it ain’t North Dakota.

    I write about what I know. I don’t know anything about putting a utility scale 500MW solar electric plant in the desert. I don’t have a dog in this hunt. I don’t know if the best approach is solar thermal, or CSP, or buying a ton of silicon PV panels. But if you want to convince me CSP is best, you’ll have to use better numbers.

  25. doggydogworld, thanks, I think I found it at hidden in the faqs regarding volumes of 10 MW per year and standard cell sizes.

    I don’t understand this compulsion to pick a winner, solar thermal (aka CSP) vs CPV or solar towers or wind or whatever. As most of the comments have pointed out, it all depends on local conditions. With the new higher efficiency CPV cells, it wouldn’t surprise me if it is cheaper in cents/KWH to put CPV in the Mohave desert than CSP particularly if they put in a cooling system like is planned for the Australian installation, but I also believe that’s not the biggest concern for the utilities. CSP has the benefit of storing energy as heat so the utility can control power output much better in an attempt to match supply to load and maintain grid stability. I have the luxury of not having to worry about such things as a consumer with a PV array on the roof.

  26. Enviromission Solar Tower

    Enviromission’s low power density was always a red flag for me. I originally calculated 2-3 W/m2, though their numbers kept shifting and it might be as high as 5 W/m2. (Flat panel PV is 150 W/m2). Can you build greenhouse for less than $10/m2? Seems unlikely.

    The Solar Tower does use thermal storage, but it seems to be uncontrolled.

  27. Southern Energy Solutions of Marietta, Georgia, United States, near Atlanta, is a dealer of Solar Thermal Hot Water Systems, Solar Photovoltaic (PV) Systems for generating electricity and Skystream Wind Turbines for generating electricity. Southern Energy Solutions is a dealer of Schüco Solar Water Heating Systems, serving Atlanta and all of Georgia.

  28. Robert,

    I currently work for Idealab, a major proponent of solar thermal energy, and am working to develop an educational site based solely around solar thermal energy on an industrial and utility scale. I was wondering if I could send you .pdf sketching out the site?

    Jamie Belsky

    P.S. Tombstone is my favorite movie. More people should see it.

Comments are closed.