I am speaking mostly from experience, from what I have seen work and fail in the field, and what I can buy to install for my clients. The reason I talk about trackers on large poles is because that is what is commercially sold right now (at least in the US, europe is ahead of us in many areas). And the biggest reason I see for failed systems is lack of maintenance (mostly batteries, but also anything that moves). Also, the number of new innovative PV systems that I have seen come on the market over the years, only to dissapear within another year... We're still basically doing the same thing as PV was in the 70's, with incremental improvements in efficiency and incremental cost decreases. I called the concrentrating PV exotic merely because I can't call up one of 200 some suppliers and buy one that meets all current electrical code, whereas I can with silicon PV modules. Maybe another breakthrough is coming, but in the mean time, alot of people will keep using coal generated power because they are waiting for those breakthroughs. I would rather see working PV systems going in today, even if they aren't all that high tech, rather than people thinking they have to wait before solar energy can work for them -- and in the mean time continuing to support coal and oil. It's not that I want to limit the new technology, but what I have seen is that the layperson holds out the possibility of a paradigm shift in the technology in the future as a reason to do absolutely nothing now. And if I recall, the original question was about concentrating sunlight on a normal old PV module -- which isn't the best idea -- they tried that at the carrizo solar plant in the early 80's, and a few years later, a whole lot of used Mud-lams (because the encapsulant turned varying shades of brown) flooded the market for off-grid use.
I do admit that this list's members are not your average layperson, and most of us won't just use the news of new inventions as an excuse for procrastinating, so I apologize for that. Zeke On 5/12/06, Michael Redler <[EMAIL PROTECTED]> wrote: > > By now, you may have noticed my resistance to "conventional wisdom" whenever > someone gives negative feedback about a particular energy scheme. Here is an > example. > > The idea of concentrating light onto PV cells is a relatively new idea in > some circles. What to do about waste heat is a natural progression in the > discussion of such technology. But, why is it seen as such an obstacle - > especially when schemes for harvesting waste heat are so abundant in energy > related discussions? > > You wrote: "...regular PV is cheap enough that the simplicity of not having > > moving parts will probably outweigh any advantage of trying to get more from > the same amount of silicon." > > > The sweeping statements are getting old Zeke. Adding trackers become > advantageous when you run out of roof. By the way PV that works on > concentrated sunlight isn't so exotic and will probably become the PV of > choice in a large percentage of applications. The large cost of > concentrating PV is likely to be offset by an increase in power conversion > requiring the use of heliostats, tracking technology and those pesky moving > parts. > > > Mike > > Zeke Yewdall <[EMAIL PROTECTED]> wrote: > > Most of the highest efficiency PV cells do use concentrators. These > are the 35% efficient super exotic ones that NREL and others are > working on. Compared to 20% which is about the highest commercial > single sun efficiency right now. In general the power produced by a > PV cell is linearly related to the energy input. More sun = more > power. So if you put 25 suns on it, you get 25 times the amount of > power from the same cell (assuming you don't change the spectral > composition of the l ight). It's not quite linear, so I think you > actually get a tiny bit more power at higher concentrations than just > the concentration ratio would imply -- say 28 instead of 25. The > problem is that a typical crystalline silicon cell also decreased its > power about 0.5% for each degree celsius the temperature goes up. So > if you increase the operating temperature of the cell from 60C > (typical for one sun) to 200C, you've just lost all the power you > gained by putting more light on it.... Plus if you get too hot, > you'll damage it -- usually the encapsulating material degrades well > before the temperature at which the actual PV cell is damaged though. > The other thing is that concentrators require tracking the sun usually > (at least to achieve more than 2 or 3 times concentration. This > introduces moving parts to the equation, and destroys one of the nice > features of PV. If it's a big central power station where you can > hire a full time maintenance operator, then go ahead. If for your own > house, regular PV is cheap enough that the simplicity of not having > moving parts will probably outweigh any advantage of trying to get > more from the same amount of silicon. > > Zeke > > On 5/12/06, Joe Street wrote: > > Actually mirrors can be used to concentrate the light from a large area > > onto a small high efficiency solar cell. It is being done. This is one > > of the justifications for the cost of high efficiency cells but the > > extra cost of the concentrators and the lengths one has to go to to keep > > from overheating the PV module unfortunately outstrip the savings the > > idea hopes to offer. Too bad but on the other hand if you are just > > fortunate to have access to heterojunction cells on the cheap then maybe > > you should go for it! You will need a liquid cooled backing plate for > > the cells but if you are crafty you might be able to use the rejected > > heat somehow as well! > > > > Joe > > > > Lugano Wilson wrote: > > > > > hi Logan. > > > > > > PV modules and solar concentrators are two different technologies and > > > unfortunately, their individual energy capture principle is > > > contradicting to each other. consequently, they can not be used at same > > > application. PV modules need to absorb all the solar radiation so as to > > > generate electricity through the module cells where as solar > > > concentrators have to reflect all the solar radiation and direct it at a > > > specific location (ie concentrated) for the purpose of heating a medium > > > that can latter generate required energy. you therefore need to choose > > > one for a specific application. however, when it comes to electricity > > > the pv modules are good due to the fact that you can size them depending > > > on your requirement starting with one module and increasing. > > > concentrators for electricity is a large scale project - not so > "modular". > > > > > > Lugano > > > > > > */Logan Vilas /* wrote: > > > > > > Would a standard PV module produce more when used with a Solar > > > Concentrator > > > or does it require a special PV module? > > > > > > Logan Vilas > > [snip] > _______________________________________________ > Biofuel mailing list > Biofuel@sustainablelists.org > http://sustainablelists.org/mailman/listinfo/biofuel_sustainablelists.org > > Biofuel at Journey to Forever: > http://journeytoforever.org/biofuel.html > > Search the combined Biofuel and Biofuels-biz list archives (50,000 > messages): > http://www.mail-archive.com/biofuel@sustainablelists.org/ > > > > _______________________________________________ Biofuel mailing list Biofuel@sustainablelists.org http://sustainablelists.org/mailman/listinfo/biofuel_sustainablelists.org Biofuel at Journey to Forever: http://journeytoforever.org/biofuel.html Search the combined Biofuel and Biofuels-biz list archives (50,000 messages): http://www.mail-archive.com/biofuel@sustainablelists.org/
