"Solar thermal" power plants like the
trough/rankin and
dish/stirling systems recently installed in NV and CA are no new thing -- other than the technology being enhanced by modern materials.
What many people do not realize, however, is that concentration systems for the average joe are in the pipeline. Some of these systems use new triple-junction hi-tech photovoltaic cells. Others use just plain old solar cells, just a lot less of them: it's a little secret of the solar industry that a lot of the cells we ship in your ordinary rooftop flat panels can handle a lot more sun than they normally do.
After the bump, I'll show you the first few products to advertise for sale to the public, and what else is in the pipeline. Plus we'll take a look at the fun prospect of using sunlight without converting it at all.
When concentrating solar power, the technical term used to count how much sunlight you are using is a "sun." A normal panel on a roof will get 1 "sun" of light. Were you to also reflect the sun onto the panel a second time, you'd be exposing it to two "suns" of light, minus any small amount of sunlight lost by the mirror. A single sun has a total power of about 1000W per square meter, and the amount of electricity you get out of the panel is divided by the number of suns worth of input power to tell you the efficiency of the panel -- how much sun gets converted to electricity, versus how much is lost by turning it into heat.
What are the advantages and disadvantages of doing this?
Well, obviously the main advantage is to get more power out of an expensive solar cell. The current silicon shortage is keeping solar panel prices high and will do so for a few years until either silicon prices drop, or alternative solar cells reach economy of scale.
One of the paradoxical things about doing this, however, is that some solar cells actually change their efficiency when you increase the amount of sunlight they are exposed to. Some cells get more efficient. So in addition to the extra power from the extra light, you also manage to harvest a greater portion of that power. In fact, new triple-junction, cells under concentrated sunlight hold the record in direct solar photovoltaic conversion, in the mid-thrity-percent range, compared with 15 to 20 percent for unconcentrated flat panels.
The drawbacks are that the solar cells need to be kept cool, so you may need a fan -- though many of the below products manage with just a heat sink on the back of the cells. Another drawback is concentrating sunlight can shorten the overall life of the cell -- but not drastically, and not enough so it matters. If you get three or four times the power from a solar cell but shorten it's "life" from 30 to 20 years, you are still ahead of the game. ("Life" is in quotes here because I don't want to be picky. A solar cell that would be considered "spent" by a solar professional actually still works, it just has a lower efficiency than it's original specification.)
Another drawback of concentrators is that they traditionally have not been as convenient to install as nice flat panel. However we'll see that a lot of that is changing and some very clever people have figured out how to deliver solar concentrator performance in a flat panel form factor or embed solar tracking in a product of manageable profile.
Finally, most concentrators demand direct sunlight and are not optimal for areas where there is cloud cover. Partly this is due to the fact that the most popular solar cells also share this trait -- you have to aim them approximately at the sun in order to catch the light. Some of the new thin film technology is better in cases where you want to collect sunlight after it has been scattered, and there are such things as omnidirectional light collectors.
So let's take a look, shall we? We'll start with two vendors who are actually advertising units for sale.
The first is an Australian operation that has worked it's way up from a mom-and-pop garage project to a serious vendor. Their odd-but-cute product is called the SunBall, because it is ball shaped. The solar cells it uses are nothing special -- just commodity cells, and the unit includes a built-in solar tracker. It works in the 5-sun range. One of the most exciting aspects of this product are that it's made in Australia and the company is actively seeking U.S. assembly and distribution partners. It's managed to sell at a $2.50/Wp (Wp = peak watt) pricetag. Not bad, not bad at all.
Second we have Pacific SolarTech's MicroPV product. This has a more-or-less flat panel profile, though a tad bit thicker than a normal panel. It also uses commodity cells, concentrating at 7 or so suns. Though it's lenses do have some omnidirectional traits, it does need to track the sun to acheive optimal efficiency -- the tracker would be a separate item. Unfortunately this company seems to be a bit cagey about current pricing at the moment. It is a Chinese owned company manufacturing in China with sales offices in CA.
Who else is planning on getting into this game? Quite a few folks actually, but we'll talk about those who've announced plans to go big with it and based on my reading are looking like they will actually do so.
First take a walk on over to Energy Innovations, a U.S. based company who will likely be sourcing parts in China with some final assembly taking place in the U.S. Their current project, the SunFlower 250, looks like a combination between modern art and a classroom overhead projector, with a built-in heliostat moving an array of mirrors. It uses commodity, though higher quality, solar cells and works in the 25 sun range. They claim they'll be shipping product this year, but have been very quiet lately -- however they have landed signifigant levels of capital investment and are by no means a "mom-and-pop" operation. Also take a look at their shelf full of prototype designs -- they have some very interesting approaches that could see some action if or when they land a cheap supplier for some critical components.
A late entry into the game is SolFocus -- a small U.S. company partnering with a large multinational, Xerox, through the PARC facility. Details are sketchy -- purposefully so -- and they seem mainly to have a nice concentrator (which is undergoing a bit of re-engineering to make it cheaper and mass-manufacturable) but haven't quite made a final determination of what kind of cells are going to be put behind it, or if they have they aren't saying. Their system is mirror, not lense, based, despite appearances, and will result in a "bulky flat panel" profile like the MicroPV. What's distinctive about this design is high concentration -- on the order of 500 suns. That would suggest they will be going for the fancy triple-junction, monocrystal high efficiency cells -- which will mean a higher power density than competitors. Somehow they are managing to stay with passive cooling even at this concentration. They do have a roll-out timeline that puts them a year or two behind competitors' claims.
Finally, DayStar, one of the U.S. companies pursuing CIGS, the most promising successor to silicon-based solar cells that I've diaried on before, has a little side project called ConcentraTIR which is a mass-producible thin plastic sheet that can focus 2 to 10 suns onto strips of solar cell materials through some tricky optics. This is likely to be a good option for use of commodity cell material while maintaining a very thin panel profile.
Finally, I promised a little look at direct solar lighting. These products use either an aimed directional collector, or an omnidirectional collector to reflect sunlight into either a fiber optic cable, or a mirrored tube and then deliver it into the darkest, dankest recesses of your house. The results can be suprisingly effective, especially when combined with a custom electric light fixture that picks up the slack to keep the amount of light in the room at a comfortable constant. One such system is the Himawari.
While these products have been a niche application due to the costs of fiber optics/etc, one could easily see them catching on as such esoteric materials scale up production due to demand.
This list is far from exhaustive, though I think I got the serious potential mass-producers listed. Anyone seen any others or got some favorites among the prototypes?
(LATE UPDATE: just for posterity, looks like another flat-profile one is on the market from Prism Solar)
(UPDATE II: Add one more company to the field: Stellaris)
