Solar Concentrators Below $1/watt
Posted by Max Dunn Thu, 24 Apr 2008 00:58:00 GMT
Today I went to an interesting Energy Seminar at Stanford. The speaker was Scott Elrod who works for Parc and studied Applied Physics at Stanford. He was talking about a product they are working on called the SolFocus which is a concentrating solar collector and their hope is to get this down to $1/watt. Here are the notes from the talk:
General PV
- Parc program portfolio ‘Cleantech’
- Normally there is a 20% price decrease for every doubling of cumulative production and PV has followed this curve.
- Under this theory, PV flat plate silicon will be $1/watt about 2020
- This curve much slower decrease than Moore’s law
- Flat PV is currently $7-9/w, works with cloud cover
- Concentrator PV $6/watt, doesn’t work in cloud cover, 1% of market
- When doing up to 5x concentration can use cheaper, silicon PV. Above this is not commercially viable until it goes above 120x and then you need expensive PV
- Tandem cells catch different energy photons and are about 40% efficient (versus 20% for silicon), but are about 100 times more expensive, about 40% efficient
- Example: Spectrolab multi-junction cells are at 40% and expects to go to 45% by 2010
- Other PV technology could theoretically get up to 70% efficiency
SolFocus
- SolFocus has 500 suns on 1cm2 that uses passive cooling. Primary mirror size is 1 ft and module is about 3 ft and 5 in thick squared and needs tracking
- Optic losses about 33%, so with 40% PV is 25% total efficency.
- So the win is lower cost because trading higher cost silicon for lower cost glass
- Should be 2 to 3 times more cost effective
- Each square foot receives about 1kw of sun, so if SolFocus is 25% efficient each square will produce 250w
- SolFocus array 12 ft by 12 ft produces about 4kW
- Next generation SolFocus each element smaller and molding the whole thing and using high speed pick-and-place to assemble
- This improves overall efficiency to 29%
- Tracking needs to be within 1% which reduces efficiency to 75%
- Temperature is reasonable: 60C for closed circuit, 70C for open circuit. (When hooked to a load, the wires carry some of the electrons away which makes it cooler)
- These multi-junction PV cells are not as sensitive to temperature as single-junction silicon
- Since these need tracking, they are not usually practical for home rooftop installation
- Manufacturing errors cause degradation; the first two molds were not good and they are still working on it.
- Si has about 10% degradation after 20 years, they hope SolFocus will be at least as long lasting
- Darpa has initaitive that is looking at refracting out each wavelength and concentrating on different PV. This is much more expensive but highest efficiency
- SolFocus aims to be under $1/w, which is the same as thin-film. Tracker is significant cost.