FunCouple5280
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quote:
ORIGINAL: samboct
Funcouple
I think the focus on $/watt has been a bit misguided. Currently, prices are artificially low by the massive overinvestment by the Bank of China in crystalline PV production which has dropped panel prices by about a factor of 3 in the last couple of years. Given that there's been no dramatic change in production technology or volume- this cannot last- but it is hell on existing solar manufacturers.
All crystalline Si PV has restrictions on sunlight angles-not just Sunpower- although given some of the coatings they're using, I wouldn't be surprised if their cells are the most critical. Essentially the photon has to fall down a long well before it can be converted to a hole/electron pair. If it hits the walls- well, too bad. Hence, what you really want is the panel to be normal (90 degrees) to the sun's rays. Consequently, for utility scale PV using crystalline Si- trackers are pretty common. I think people are using both single axis (relatively cheap and with falling prices) and two axis trackers (more expensive-but gets the most out of the cell. The markets between utility and residential keep shifting- I think utility scale is now larger than residential, but residential may be growing faster in the US. Think that's true globally as well. The US is about a quarter of the global PV market IIRC.
For rooftop installations though- crystalline Si may not be the best technology for the aforementioned loss of efficiency due to angles away from normal. Instead, thin film solar has an advantage here, because the photon has a lot less distance to travel inside the cell- and it's much less likely to bump into a wall and be lost. (generates heat) Even though the thin film cells still have lower peak efficiency than crystalline Si, over the course of a day or a year- they may actually collect more energy. And they don't need trackers as much.
As an aside- I appreciate your comments that Sunpower is hard to deal with. I have a very theoretical knowledge of this stuff- my focus has been on looking at the materials used in renewables for clients, but it doesn't mean that I've gotten into actual installations.
However, not all PV is improving at the same rate. As I've pointed out previously- crystalline Si has a theoretical max efficiency (Schlockley limit) of 29% conversion- and Sunpower is at 24%. They're running into diminishing returns. Thin film cells have got more room for improvement- hero CIGS has broken 20%, but manufactured cells I think are still around 14% or so. More room to improve. Semprius could be a game changer since they can use GaAs without running into cooling issues.
I don't think $/Watt is misguided at all. If it costs x to install and will produce y power over its life, then dividing one into the other gives you the overall cost of the juice. If an installed solar system produces power at a cost of $0.28/kWh and the utility is charging you $0.11, as a consumer you are going to say keep the coal. The price is a huge factor. The last time I dealt with SP was before the collapse of PV prices. PV was in the $2/W range and SP was in the mid $4's. Just cause the Chinese have bottomed out commercial solar, doesn't necessarily mean SP dropped in price. Right now, I would totally take advantage of current PV prices. It is rocking awesome.
When I talk about angles I am talking about concentrators versus conventional PV. Lighy coming in at a 20 degree angle on standard PV still produces power at the majority of rated capacity, even on Si panels. At 3 degrees a concentrator goes to zero. For the 40% more power that is generated with 2-axis trackers with PV, I dont' think it is worth the money at all. The trackers are expensive, you lose real estate to deal with movement and they fail. DIA the Airport in denver has a multi mega-watt solar farm on a single axis trackers. I fly 20-30 per year. Everytime I drive past those things about 10%-20% are always malfunctioning. A single axis tracker boosts performance by about 10%, so essentially, they pissed money away on that tracker because they always have about 10% down and requiring service. If it were fixed, they would have gotten more panels per acre, and never had the maintenence of fidgetting with a mechanical system stuck outdoors.
I think Si is ideal for residential roof top. at 18% module efficiency, most suburban US homes have enough roof realestate necessary to power the home. Especially with some efficiency upgrades inside...I know, my roof is ample and after the upgrades I only have to cover 80% of the southern roof to generate 115% of my power needs. Plus Si is durable. If we would get away from PVA adhesives which yellow and derate the capacity of the solar panels with time and move to silicone liquid encapsulant, you can have Si panels that are still at 97% rated capacity at 25 years and easily last 50+ years. Dow corning has pioneered that technology.
I like Cigs but I have yet to see Cigs modules that are both cost friendly and actually performing above 12% outside of the lab. However, they will not last as long as Si from what I understand. For Cigs to really be useful in broad applications, they need to be dirt cheap and they are pricier than crystalline PV right now.
There is some interesting work being done with nano technology and solar. Since light is EM radiation like a microwave or a radio wave, it can be collected with an antenna. One group devoloped a carbon nano antenna that is stupid efficient at collecting light. However the power is currently useless as the frequency of that power is something like several TeraHertz or something. Basically there are no know switching circuits that can operate at those frequencies and convert that power into something useful. Another I saw as using bucky balls on Si panels to improve the collection spectrum. In that case you can get the theoretical efficiency of Si well above 29% without costly elements being used in manufacture.
Ultimately, I think we are 10yrs away from the real solar revolution. Several things will happen, we will have better cost higher efficiency PV. The cost of convential power will have increased to a point were it just starts to make general sense to do this. Finally, maybe, we will have some batteries with a higher energy density than current Li technology permits.
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RE: The realities of renewable energy. - 
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).. they got that money selling oil to the US and so they are looking for other stuff to sell you once the oil runs out.. they want US dollars to keep flowing into their pockets.. 
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