5 ms·

I always wondered why we did not just use prisms to separate the different wavelengths, then capturing selections of the spectrum with a variety of simpler, uns

I always wondered why we did not just use prisms to separate the different wavelengths, then capturing selections of the spectrum with a variety of simpler, unstacked panels. Perhaps one could even deflect the infrared into a more conventional, presumably more efficient, heat collector while the higher frequencies are directed to true photovoltaics.

maxerickson 9y ago
People with excess roof space (and whatever other space) look at cost before they look at efficiency. Half the roof here would provide plenty of power, the problem is that it would be expensive.
klodolph 9y ago
Think of how solar is an investment: you pay money up front, use up a certain chunk of land, and you get energy over the next 25 years. Imagine panel A which costs $100 and has 22% efficiency, versus panel B which costs $500 and has 30% efficiency. No point in buying panel B, since you can buy 5x panel A for the same price.
- jcbrand 9y ago
  But then you'd also need to cover 5 times the area, and land also costs money.
  - mikepurvis 9y ago
    I'm doubtful that land area is really a significant cost for most solar installations. Small ones go on rooftops that people already have, and large ones go on marginal land in the middle of nowhere that's cheap. If there's someone with knowledge of the numbers, I'd be interested to be shown otherwise.
    - philipkglass 9y ago
      You are correct. "Small" utility-scale solar projects of 1-20 MW capacity take 7.6 acres of land per megawatt-peak, for fixed-tilt ground mount systems: http://www.renewableenergyworld.com/articles/2013/08/calculating-solar-energys-land-use-footprint.html http://www.renewableenergyworld.com/articles/2013/08/calcula... Fixed-tilt utility scale systems just recently fell to $0.99 per watt-peak in the US: https://www.greentechmedia.com/articles/read/Sunshot-1-Per-Watt-Solar-Cost-Goal-Mission-Accomplished-Years-Ahead-of-S https://www.greentechmedia.com/articles/read/Sunshot-1-Per-W... You can buy 124 acres of land in California's sunny Imperial County, near existing solar farms, for $95,000: http://www.landwatch.com/Imperial-County-California-Land-for-sale/pid/3446602 http://www.landwatch.com/Imperial-County-California-Land-for... If you turned that land into a solar farm you could fit about 16 megawatts of fixed-tilt solar arrays on it. 16 MWp of installed solar equipment would cost $15.84 million at $0.99/watt and the land is $0.095 million. Land accounts for only 0.6% of the combined costs. (A 16 MWp farm is small by utility-scale project standards and probably would not cost only $0.99/watt because of dis-economies of small scale. I cited $0.99/watt to set a conservative bound on how much cost the land component represents in a utility scale solar project.)
  - chriswarbo 9y ago
    If the cost is right, land won't be an issue. If solar tech were cheap and rugged enough, it could be added to paint, tarmac, billboards and many other artificial surfaces, even at very low efficiency. I've seen work in this direction with organic molecules (i.e. plastics).
    - klodolph 9y ago
      I'm not optimistic about solar power being added to paint, tarmac, or just wherever you want. See for example the dumpster fire that is Solar Roadways. At this point, there's enough land / rooftops for proper PV installations that easily last decades, so trying to shoehorn fragile PV in places where it has to withstand daily abuse, like tarmac, stinks of bad engineering. Maybe that will change, but it doesn't need to change, because we still have plenty of places to stick solar.
      - chriswarbo 9y ago
        Yes, to be clear I didn't mean the sort of rigid, silicon/glass PV panels we have right now; and solar roadways is evidence enough that it would be a bad idea. I meant something more like a polymer, bought by the bucketful and mixed in as an additive.
tedsanders 9y ago
As usual, cost is the issue. Both the cost of the optics, the cost of tracking, the cost of imperfect tracking, and the cost of the complexity in the design and installation. I know some academic research labs have looked into arrays of microlenses & prisms, which sound interesting, but I haven't heard of any commercial products. Googling for micro prisms and solar cells will show you some projects. Ultimately, I think it's just much easier to install a simple rectangular slab with two wires coming out. And the costs of solar cells are so cheap that they're probably comparable to the cost of the optics you'd want to lay above them. I also imagine that balancing the current-voltage characteristics of the cells could be challenging when light at different times of the day has different spectra (e.g., you wouldn't want diminished performance in reddish sunsets).
gene-h 9y ago
This approach has been tried before and was used to make a solar cell with record efficiency[0]. This approach might be needed to get up to 50% efficiency. [0]http://www.electronicproducts.com/Sustainable/Solar/Prism_device_helps_scientists_break_solar_efficiency_record.aspx http://www.electronicproducts.com/Sustainable/Solar/Prism_de...

maxerickson 9y ago

People with excess roof space (and whatever other space) look at cost before they look at efficiency. Half the roof here would provide plenty of power, the problem is that it would be expensive.

klodolph 9y ago

Think of how solar is an investment: you pay money up front, use up a certain chunk of land, and you get energy over the next 25 years. Imagine panel A which costs $100 and has 22% efficiency, versus panel B which costs $500 and has 30% efficiency. No point in buying panel B, since you can buy 5x panel A for the same price.

jcbrand 9y ago
But then you'd also need to cover 5 times the area, and land also costs money.
- mikepurvis 9y ago
  I'm doubtful that land area is really a significant cost for most solar installations. Small ones go on rooftops that people already have, and large ones go on marginal land in the middle of nowhere that's cheap. If there's someone with knowledge of the numbers, I'd be interested to be shown otherwise.
  - philipkglass 9y ago
    You are correct. "Small" utility-scale solar projects of 1-20 MW capacity take 7.6 acres of land per megawatt-peak, for fixed-tilt ground mount systems: http://www.renewableenergyworld.com/articles/2013/08/calculating-solar-energys-land-use-footprint.html http://www.renewableenergyworld.com/articles/2013/08/calcula... Fixed-tilt utility scale systems just recently fell to $0.99 per watt-peak in the US: https://www.greentechmedia.com/articles/read/Sunshot-1-Per-Watt-Solar-Cost-Goal-Mission-Accomplished-Years-Ahead-of-S https://www.greentechmedia.com/articles/read/Sunshot-1-Per-W... You can buy 124 acres of land in California's sunny Imperial County, near existing solar farms, for $95,000: http://www.landwatch.com/Imperial-County-California-Land-for-sale/pid/3446602 http://www.landwatch.com/Imperial-County-California-Land-for... If you turned that land into a solar farm you could fit about 16 megawatts of fixed-tilt solar arrays on it. 16 MWp of installed solar equipment would cost $15.84 million at $0.99/watt and the land is $0.095 million. Land accounts for only 0.6% of the combined costs. (A 16 MWp farm is small by utility-scale project standards and probably would not cost only $0.99/watt because of dis-economies of small scale. I cited $0.99/watt to set a conservative bound on how much cost the land component represents in a utility scale solar project.)
- chriswarbo 9y ago
  If the cost is right, land won't be an issue. If solar tech were cheap and rugged enough, it could be added to paint, tarmac, billboards and many other artificial surfaces, even at very low efficiency. I've seen work in this direction with organic molecules (i.e. plastics).
  - klodolph 9y ago
    I'm not optimistic about solar power being added to paint, tarmac, or just wherever you want. See for example the dumpster fire that is Solar Roadways. At this point, there's enough land / rooftops for proper PV installations that easily last decades, so trying to shoehorn fragile PV in places where it has to withstand daily abuse, like tarmac, stinks of bad engineering. Maybe that will change, but it doesn't need to change, because we still have plenty of places to stick solar.
    - chriswarbo 9y ago
      Yes, to be clear I didn't mean the sort of rigid, silicon/glass PV panels we have right now; and solar roadways is evidence enough that it would be a bad idea. I meant something more like a polymer, bought by the bucketful and mixed in as an additive.

tedsanders 9y ago

As usual, cost is the issue. Both the cost of the optics, the cost of tracking, the cost of imperfect tracking, and the cost of the complexity in the design and installation. I know some academic research labs have looked into arrays of microlenses & prisms, which sound interesting, but I haven't heard of any commercial products. Googling for micro prisms and solar cells will show you some projects. Ultimately, I think it's just much easier to install a simple rectangular slab with two wires coming out. And the costs of solar cells are so cheap that they're probably comparable to the cost of the optics you'd want to lay above them. I also imagine that balancing the current-voltage characteristics of the cells could be challenging when light at different times of the day has different spectra (e.g., you wouldn't want diminished performance in reddish sunsets).

gene-h 9y ago

This approach has been tried before and was used to make a solar cell with record efficiency[0]. This approach might be needed to get up to 50% efficiency. [0]http://www.electronicproducts.com/Sustainable/Solar/Prism_device_helps_scientists_break_solar_efficiency_record.aspx http://www.electronicproducts.com/Sustainable/Solar/Prism_de...