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197 comments on Concentrating On The Important Things - Solar Thermal Power
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197 comments on Concentrating On The Important Things - Solar Thermal Power
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Because of the recent EROEI discussion, I'd give this link for a CSP estimate: http://www.ases.org/divisions/electric/newsletters/2006-04.html#roi
27 with storage and 44 without with Eout in electricity, not thermal.
By combining CSP district water heating with PV I get a cost estimate for electricity at under a penny per kWh here: http://mdsolar.blogspot.com/2008/03/lux-lucis-tepida.html
The water cools the silicon allowing a much higher concentration of sunlight. Also, the water shields the silicon from cosmic ray induced defects so that it lasts much longer. There may be immediate potential for 3 GW average electric power in the US by this method.
There is a lot of potential for CSP.
Chris
Hey read this: http://www.abc.net.au/science/articles/2008/01/16/2139711.htm
Imagine 99.95% of the light energy absorbed as heat through a coat of these nano-tubes on the inner tubes of these CSP stations. I imagine with use of vacuums and Stirling engines that it would essentially be 50 % + efficient solar power. A revolution in nano-tube production is needed to bring down cost though, they can run more than 250,000$ a ton. I can't see how coal or nuclear could compete with a system like this, plus the only emissions are from the materials manufacture which could be converted over too renewable sources essentially, emission free power.
I'm gonna stop before I start to sound like a techno-phile, ewww
Regards,
Crews
The standard coatings on domestic vacuum tube solar thermal water heaters using multilayers of materials like nickel sulphide and oxide and aluminium nitride already achieve absorptances in the visible of 94% while having emittances in the long infra-red (to stop re-radiation) of 8%. The gain from going from 94% to 99.95% is very little and the cost of going from a relatively low technology of such multilayer films to carbon nanotubes is at present huge. It will have to fall a long way to make it worth such a small gain
The article does not quote the infra-red emittance of the carbon nanotubes but this is a vital parameter. Since by Stefan's law, radiated energy rises as the fourth power of the absolute temperature and these utility sized solar thermal units operate with their absorbers at a much higher temperature than domestic units the re-radiation losses will be much higher. A small increase in infra-red emittance will easily wipe out the gain from a slightly higher visible absorptance.
I think that reducing reflectivity helps quite a bit, that was one of the main effects in improving efficiency in BigGav's second PV link on multicrystalline silicon. But, the main limit for this type of PV is the electronic bandgap which ends up only being responsive to a portion of the solar spectrum. Usually, PV is used with concentrators when it is multijunction so that there is more than one bandgap. That material is expensive because it is complex to manufacture and it is optimized to run hot, though not as hot as concentrated solar thermal. It is sometimes worth it though because you need less of it. What I have in mind is to use regular silicon and run it cold, but then use the low grade heat from the cooling water to save some energy in home water heating thoughout a small town. Because there is no need for really high tempertures and because existing infrastructure is reused, the cost comes in pretty low. Lower reflectivity in the panels means that much more heat for the water.
Chris
Chris;
In response to your blog entry, am I clear that the PV is in the water, facing UP (clear tank-roof), or is it attached to the underside, facing heliostats?
In either case, it sounds like an interesting synthesis.
-If immersed, do you have a sense of the Visible Light transmissivity through that much water, and it's effect on PV absorbtion?
-Second, did you find a good source of info for how much light a water-cooled PV panel can be subjected to, and how this affects it's potential output and lifespan? You touch on these, but I'd love to see some documents on test-results for such setups.. I would hope that it's possible to toss maybe 3 to 6 'Suns' at a panel that is aggressively cooled to boost it's yields, without compromising on its durability. Your proposal to shield the PV from cosmic rays with water sounds good up front, so has it been tried out to any degree that you are aware of?
Best,
Bob Fiske
Hi Bob,
The idea is to hang the panels from the bottom of the tower and cool them with running water on the unilluminated side. There is a program in New Mexico that just got funded to do this kind of plumbing. I mentioned it here:
http://mdsolar.blogspot.com/2007/07/new-mexicans-conspire.html
Sunlight does not harm silicon though it can have an effect on epoxies and such in the rest of the panel structure. Heat cycling can cause delamination of electrical contacts. On the cosmic rays, this has been an issue in the semiconductor industry for a while, and is quite well known for space applications. Water is used as a cosmic ray shower detector in the Auger Observatory and it would not see them if it could not stop them. Basically, at those energies it is mass that makes a difference though some metals can produce a secondary X-ray flux which can be a problem for shielding humans. Since ground radioactivity is lower energy, 50 meters of air should be a help. It seems to me that all you would need to do to check would be to put a scintillation counter in place and hang a second off a boom or put it up on a pole nearby. You should have enough data in a week or less. If you have a tower in mind, I can try to do a more detailed calculation of the relative flux just below and out away from the tower. I know of one proposed experiment to put some panels in the Goldstakes mine for a long time to check their degradation. Don't know if it went forward. It is easier to look at data from space or take a panel to an accelerator to understand the degradation mechanism.
Other degradation mechanisms owing to water getting into the panel frame might be avoided in this enviroment as well. It should not be too difficult to keep the panels warmer than the ambient environment at night since the warmed water is available so that even with a small leak, condensation within the panel might be avoided. This would tend to protect anti-reflection coatings and electrical contacts.
Chris
There are at least 2 typos in the table. The sum of the listed embodied energies (without storage) totals to 175.2GWh, not 174.2GWh. The EROEI calculates to 34, not 44. Still good, but not 44.
I agree. Thanks for catching that. I notice also that no estimate is made for running the heliostats or pumping the salts. I'd like to see more thorough work on CSP if you know of any.
Chris
I would like to see an EROI estimate of Ausra's CLFR. Considering the compactness and lower structural (mirrors close to the ground) and material requirements (low temperatures and pressures) it should do pretty good.
Very nice! I was wondering when someone would innovate a combined PV/CSP array.