The Guardian had a story yesterday on concentrating solar collectors. They have caught on to something I've been saying for a while: concentrating mirrors and heat engines can produce solar electricity less expensively than photovoltaic cells. Currently, we are able to store heat less expensively than electricity.
Whether the electricity comes from direct sun, or stored heat, Dr. Gerhard Knies and Dr. Franz Trieb are quoted pointing out that the lower temperature waste heat from electrical generation by this means can purify water and power air conditioning, providing host countries with additional value.
Since this type of power is only economical in deserts with strong sun and few cloudy days, the power has to be transmitted long distances -- which Knies and Trieb say is practical. Power loss even between Libya and London would be quite reasonable.
Comments
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sunflower Posted 5:02 am
29 Nov 2006
http://www.harbornet.com/sunflower/dishsteam.jpg
C...
The Oz people are doing big dish pv in a big way.
http://www.solarsystems.com.au/documents/SolarSystemsMedi...
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sunflower Posted 5:04 am
29 Nov 2006
CPV (concentrator photovoltaics) is new technology. I hooked up high-intensity pv to a small dish in 2002.
http://www.harbornet.com/sunflower/litxs.jpg
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Gar Lipow Posted 5:42 am
29 Nov 2006
Concentrating PV is great. I have not checked lately, but I believe the Austrialian concentrating Sunball system is now commercially available. There are a lot of commercial technologies out there, and a lot more on the verge of becoming commerical. The main bottleneck is storage. You can store high temperature heat, suitable for generating electricity TODAY -at the a cost equivalent of $30-$40 per kWh of capacity. Nothing for sale today can match that. And if we are talking near term breakthroughs, the NREL thinks this cost can be lowered to $15 per kWh equivalent.
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sunflower Posted 6:07 am
29 Nov 2006
For a story on burning mirrors see...
http://people.linux-gull.ch/rossen/solar/deathray.html
Renewable dispatchable power is not required until very large low-cost deployment has occurred.
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Gar Lipow Posted 7:02 am
29 Nov 2006
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sunflower Posted 7:14 am
29 Nov 2006
So many years, so much talk....
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GerryWolff Posted 8:36 am
29 Nov 2006
http://www.trecers.net/index.html
and
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GerryWolff Posted 8:40 am
29 Nov 2006
There is more information about CSP and the 'TREC' ideas at:
http://www.trecers.net/index.html and
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GerryWolff Posted 8:44 am
29 Nov 2006
There is more information about CSP and the 'TREC' ideas at: http://www.trec-uk.org.uk/index.htm and
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GerryWolff Posted 8:46 am
29 Nov 2006
Gerry
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sunflower Posted 9:20 am
29 Nov 2006
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GerryWolff Posted 7:01 pm
29 Nov 2006
Gerry
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caniscandida Posted 9:51 pm
29 Nov 2006
Thanks, Sunflower, for correctly identifying Archimedes as the brilliant (he may have invented calculus) but morally questionable (he ran around naked, shouting "Eureka!") mathematician who allegedly focussed sunlight with large mirrors on the Roman battleships blockading his city of Syracuse in Sicily.
(If the good-bit-earlier Aristotle had been at all interested in things like that, Alexander the Great would have drafted him, and who knows, the Hellenistic World might have ended up stretching to the mouth of the Yangtse.)
My guess is, if Archimedes' focussed-sunlight technology really worked, the memory of how he did it would have been preserved by the victorious Romans (yes, no surprise, they eventually won) and conserved in their arsenal.
Or do I over-estimate the intelligence of the Romans? -- not hard to do, actually. I remember the cover of a magazine, Scientific American or something of that level, around ten years ago, showing Archimedes dead on the floor, next to a complicated geometric figure that he just drew, with circles and squares and tangents and secants, with the pointy end of a five-foot compass drilled into his chest, and his blood spilling all over the circles and squares; and above him, holding the turning end of the compass, was a dullard-faced Roman kid in armor and with a sword at his side, and with a stupid sheepish smile on his dullard face.
Chickens are our cousins!
So are other sensitive animals!
Enough is enough!
No more factory farms!
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Gar Lipow Posted 3:27 am
30 Nov 2006
I wonder if Archimedes was really morally questionable in this case. They were, after all,designed to placed in a light-house. If they had worked they would have been one of the truly defensive weapons ever developed. Your army has to bring its ships in for attack before they are in range to be burnt. Of course if you attack at night or in cloudy weather, nobody can do anything to you - which certainly limits their usefulness. (Night attacks in those days were pretty problematic though, weren't they? And how common was cloudy weather in that particular location.)
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Jianguo Xu Posted 6:18 am
01 Dec 2006
Currently Boeing and Emcore are the leading companies in producing multijunction PV's.
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Jianguo Xu Posted 12:37 am
03 Dec 2006
Here is why it makes sense: assume concentrated solar thermal or PV has a net efficiency of 33.3%, including the transmission losses (we are not there yet, but may be close). Assume for heating or cooling in buildings and homes, we have a coefficiency of performance (COP) of 3. We get a "round trip" efficiency of 1. More importantly, the capital cost is very high.
The current simple solar water heaters of course do not have an efficiency of greater than 100%. However, if a thermally activated heat pump with an COP of, say, 2.0 for space heating and 1.3 for air conditioning, is used, then the overall COP can be greater than 1, beating the more expensive version.
Of course, there are other sources of energy we should use in solving space heating/air conditioning energy source issue. Geothermal simply stands out among them. Combining geothermal energy with solar thermal heat pump is a great way of greatly reducing energy consumption in HVAC area. My understanding is that space heating and cooling consumes close to 1/3 of the total energy consumption of the society. Therefore, we are not talking about a small issue - it is almost as important as that of transportation.
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amazingdrx Posted 2:51 am
03 Dec 2006
You said that manufacturing paced to solar and wind power availability would be cost prohibitive! Hehehey.
I guess it will be limited to melting heat storage salt eyyh?
The economies here are obvious. Not only that, but PV cells mounted at the outer edges of the furnace aperature would provide additional cogeneration efficiency.
And have you heard of infrared pV cells that will generate power directly from the glowing solar furnace and it's molten outflow? No? I'm not surprised.
I have to add that these solar furnace manufacturing cogeneration facilities ought to be built on already devestated industrial sites instead of using untouched desert land. Even a desert is an ecosystem worth preserving, and plenty off contaminated sites are available thanks to the horror of present and past industry self (no) environmental regulation.
With the profits partillay used to clean up the mess left behind.
http://amazngdrx.blogharbor.com/blog
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sunflower Posted 7:29 am
03 Dec 2006
As it turned out, low was the big market (food processing, etc.) and high temperature markets were small (excepting thermal power plants). Solar concentrators are efficient supplying IPH for low and medium temperatures.
The Swedes are effective at collecting industrial waste heat for district heating applications. TPV (thermal pv) is only about 10% efficient.
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Gar Lipow Posted 8:20 am
03 Dec 2006
>You said that manufacturing paced to solar and wind power availability would be cost prohibitive! Hehehey.
>I guess it will be limited to melting heat storage salt eyyh?
Yup. Because solar thermal does not need to be attended according to the sun's schedule. You can pretty much schedule operations labor - a certain amount to be done during the day to prevent short term failures, a certain amount to be done at night to prevent interference with generation.
Operate a factory only when the wind blows, or only when a sun is not behind a cloud, and you have a lot people spending time standing around. Also you use a lot less of the capital investment your equipment. You are a lot better off using only 30%+ of the nominal capacity of a wind generator than you are using only 30% of the nominal capacity of a factory. Don't know many factories that don't operate on at least 12 hours per day. Saying you should not operate a factory only when the wind blows or sun shines is not saying it is too expensive to operate a factory based on solar energy or wind. It simply makes more sense to use backup or storage rather than shut down the factory at random intervals.
Of course where you are perhaps about 10% right is that some industrial process can store results - so in limited cases this may be the cheapest storage means. For example if you have a process that uses compressed air anyway, it makes sense to make extra compressed air from variable (for good reason I don't use the word intermittent) power, and store that. Similarly, large scale refrigerators, freezers, and chillers can be modified to store cold fairly easily - and thus take advantage of variable power. But I would not do this for classic assembly lines, or mechanical power.
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amazingdrx Posted 4:24 pm
03 Dec 2006
http://amazngdrx.blogharbor.com/blog
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sunflower Posted 12:09 am
07 Dec 2006
Boeing subsidiary Spectrolab Inc has achieved a new record in terrestrial concentrator solar cell efficiency. Using concentrated sunlight, the company has demonstrated a photovoltaic cell that converts 40.7% of the sun's energy into electricity, as verified by the U.S. Department of Energy's National Renewable Energy Laboratory (NREL).
http://www.semiconductor-today.com/news_items/DEC_06/SPEC...
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amazingdrx Posted 12:35 am
07 Dec 2006
Conservation plus concentrating solar powers this Madison, Wi home. Now if he collects the heat from his PV concentrator as well, who knows? Maybe heat AND electricity all from the sun.
http://amazngdrx.blogharbor.com/blog
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sunflower Posted 1:24 am
07 Dec 2006
High-intensity pv requires aggressive cooling which limits the discharge temperature. Cogeneration of heat and power is easy if the primary application is heat -- the receiver inlet is cold water, a good location for cells and the second half of the receiver is hot, not a good location for cells.
Overall, the production of heat and power is efficient and cost effective. System energy and carbon return on investment is less than one year (I am hoping for a future EROI of less than six months). In 25 years the energy return is better than 25 times the energy investment.
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amazingdrx Posted 11:18 pm
08 Dec 2006
Suitable for cooking as in the Gaviotas design. They operate pressure cookers with hot oil from solar collectors.
What temperature can an inexpensive PV cell bought as a factory second by the pound withstand? I guess experimentation is in order.
Have you seen the Franklin Fuel Cell website, their technology is interesting. Not solar, but great backup generation for renewables that would run fine on biofuel produced from solar collector/algae growing systems.
http://amazngdrx.blogharbor.com/blog
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sunflower Posted 12:52 am
09 Dec 2006
Briefly, oils in concentrators have problems -- low heat transfer, laminar stagnant layers, tarring on receiver walls, leaks (requires welded pipe joints), and expensive pumps. Latent heat transfer (boiling water) is most efficient, followed by sensible heat transfer with turbulent water flow.
PV heat tolerance depends on PV materials, and I am not sure about the new 40.7% type III-V. These high-intensity PVs (HIPV) can tolerate 300 C. (and are soldered to heat sinks) but are only operational below 100 C., and most efficient at 25 C., though 60 C. is ok.
Heat sinks have thermal resistance, the cell temperatures are higher than the coolant discharge temperatures. Like heat engines, HIPVs need cold sinks, like rivers or air cooling towers, or preheat for thermal loads. Heat sinks used for computer chips are also useful for HIPV. These sinks are either sensible matrix turbulent flow or latent heat pipes with a fan.
Everybody loves solar electricity but solar concentrator thermal displacement of fossil fuels for HVAC (heating, ventilation, air conditioning) and IPH (industrial process heat) are much larger markets, more profitable, and a quick displacement of carbon emissions. For these applications it would be very cost effective to cogenerate some power off the top of the cycle. Square kilometers of HIPV (dedicated only for power) glass solar concentrators would be my second choice. (Acrylic Fresnel lens also have problems -- chromatic aberration, UV degradation, dirt adhesion, and cost.)
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amazingdrx Posted 1:50 am
09 Dec 2006
I am wondering if the PV cells can be mounted to accept the shorter light wavelengths and reflect the hottest infrared, since that does not generate electricity in most solar cells. The hottest solar energy absorbed in a separate collector mounted near the PV cells.
BTW, have you heard about infrared PV cells? Might be great in a concentrator setup.
The oil solar collector in the Gaviotan design reached temeratures of up to 400 degrees F.
The latest hot water heating solar design being promoted by the local utility company uses vacuum tube insulation around the collector tubes, greatly increasing the efficiency in our cold winter climate of northern wis.
http://amazngdrx.blogharbor.com/blog
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sunflower Posted 2:20 am
09 Dec 2006
Thermal pv (TPV) is only 10% efficient.
Indirect sunlight from clouds and blue sky is only 15% of what direct sunlight contains so collecting indirect light is not worth the effort. Those evacuated tubes are expensive without much (if any) benefit.
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Gar Lipow Posted 4:49 am
09 Dec 2006
For cloudy climates such as I live they can be worthwhile for space heating.
With normal flat plate collectors you get plenty of output in sunny weather, not so much in grey weather. (But some. Even normal flat plate collectors collect some indirect light.)
But if you put in evacuated tube collectors, you get peak collector efficiency during the winter. So if you make a collector that will prodide (say) 65% of your spacing heating on a cloudy day it won't overproduced on sunny day - only rising to 85% or 90% of needs. So you have a collector that will supply your needs during really cold cloudy weather (when you need it most) and won't have to dump heating during the sunny weather. Overall it produces less heat than a flat plate collector of the same area- but it produces more of it during the winter and fall when you most need space heat ing. (And it will produce during spring too - less efficiently, but you have more heat available).
Note that this works specifically for space heating. You need hot water all year round, possibly more in summer than in winter (more cleaning). So a flat plate collector almost certainly makes more sense for water heating.
If you look at the output curves for the Pacific Northwest, an evacuate tube collect produces about 85% to 95% of power year round that flat plate does. But it produces a much higher percent of that output in the winter - and so is preferable for cold cloudy climates for space heating. Again we are talking space heating , not hot water,not electricity, not most industrial uses.
Incidentally there might be an argument for this even with district heating. You are reducing the amount of storage you need, but using more expensive collectors covering more area. Higher collector costs, vs. lower storage volume. The optimum would be very specific to circumstances, solar panel costs, storage costs, storage losses, particular climates.
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sunflower Posted 6:13 am
09 Dec 2006
Holy Solar BatmanSolar energy is divine. It is far more difficult to make solar energy cost competitive.
The system must be very low cost, have low maintenance cost, last a long time, and be sized to the load (after load efficiency improvements.
To be cost effective, a solar system must supply nearly all available sunlight to a load. A solar system sized (or slightly oversized) for peak summer irradiation will supply a small fraction of a winter load. These are hard realities about isolated solar energy supply systems. That's ok, the solar market is still over $1 trillion, a lot of negative carbon.
In a good system, flat-plate thermal collectors lose 15% to 30% from heat loss (there goes the 15% gain from clouds), plus 8% to 16% front surface reflection(s), 15% from dirt, 10% from less than black paint, 15% from heat transport, and some significant loss from thermal inertia and cosine angles to the sun. System (not collector) annual efficiencies have been measured to be about 35% of incident light, at best.
Be shy of promoter economics, whether dish concentrators, or advanced stationary collectors, or subsystems like HIPV. Only trust independent lab tests conducted under peer review, like that found at NREL and Sweden.
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Gar Lipow Posted 2:41 am
10 Dec 2006
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sunflower Posted 3:25 am
10 Dec 2006
All solar collectors in cloudy climates are less cost effective. If such collectors do not efficiently collect summer insolation then they would probably not amortize at all. Cost effective solar energy systems are possible in Seattle type climates, its just not easy, requires careful engineering.
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Gar Lipow Posted 4:01 am
18 Dec 2006
I know that is not true, because I've seen them do it.
Also if you look at the SRCC ratings:
http://www.solar-rating.org/ratings/OG100DIRECTORIES/OG10...
and scroll down to the glazed collector sections (page 26 if your print driver is 8.5X11) you will see that flat plate collectors do indeed generate some heat in cold cloudy weather.
Incidentally, the fact that natural zeolites are as efficient as synthetic zeolites for storing heat up to around the boiling point of water has been known at least since 1994. Since you have worked in this stuff, I wonder if you know what the economic and technical barriers are for using this for storage. The zeolites themselves are cheap, and they take up about a fifth of the room water would. It the control equipment expensive? Or is there a huge thermal loss in the adsorption/desorption cycle? In short, is there is there a good reason those self-cooled beer kegs they sell Germany is one of the few commercial products that use this principle?
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sunflower Posted 12:50 pm
18 Dec 2006
The industry supported solar collector certification (created 1980) confirms that flat plate collectors do not supply hot water during cloudy cold days. However, they do supply hot water in cloudy cool climates. Even Seattle has 25% chance of sun during December.
I noticed that their day sun data matched the annual average solar radiation for Albuquerque and their day cloud data matched the annual average solar radiation for Seattle.
I had to convert mj into kWh to read the data. (1 mj = 0.278 kWh (I think)) Typical cloudy full sky irradiation is 0.15 kW/m2, about half the light used in the certification test.
They also have constant flow tests so the collector is operated cold during cloudy simulations and hot during sunny simulations.
Using their numbers (on the Skyline 20-01) the collector is 25% efficient supplying hot water under sunny simulations and 5% efficient supplying cold water under cloudy simulations. The ratio of energy supplied is ten (sun) to one (cloud), which would be zero under actual clouds.
There is a better way to visualize solar collector performance operating at constant temperatures. 1 kW light per square meter (1 kW/m2) is available during the high noon sun and 0.15 kW/m2 light during cloudy weather. If a collector loses just 15% from heat loss then the 15% of sun from clouds is a total loss. Normally, collector systems lose more than 40%, making the sunny sun very important.
Seattle gets about 1200 kWh/m2/year light. At 25% annual efficiency (35% possible) the collector is worth 300 kWh/m2/year, if displacing electricity at $0.10/kWh that is worth $30/m2/year.
A good source is the irradiation data from NREL.
http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/atlas/...
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