5 ms·

This is the current version of that chart: https://www.nrel.gov/pv/assets/images/efficiency-chart.png https://www.nrel.gov/pv/assets/images/efficiency-chart.png

This is the current version of that chart: https://www.nrel.gov/pv/assets/images/efficiency-chart.png https://www.nrel.gov/pv/assets/images/efficiency-chart.png This cell is the blue dot "Kaneka". Multijunction cells are very expensive to make. The reason the multijunction cells in that chart all have concentrators is that without them, the cost is ridiculously too much to even consider. This particular cell is noteworthy because it is cheap enough that you can eschew the added cost and complexity of the concentrator and just use more cells and potentially still be cheaper.

jacquesm 10y ago
> potentially That's the operative word here. And that is far from a run race with this particular technology, it is going to be close enough that it bears watching but not so good that it is a slam dunk winner.
- nojvek 10y ago
  To be honest it's a lot more economical to have cheap large mirrors on your roof directing sunlight towards a concentrated spot of PV cells of higher efficiency that are somewhat expensive. You could use some of that energy to have tiny motors that track the sunlight. This would net in more energy and less cost per square meter right?
  - jacquesm 10y ago
    I've done a lot of experimenting with that. Here are some of the (surprising!) results: - you only need one motor to aim a whole array of mirrors if you're willing to make some exotic gears - the lifespan of the cells will shorten measurably - you will need to cool the cells if you don't want them to die very quickly - there will be a serious fire risk
    - ballenf 10y ago
      Are there cells designed for higher intensity than others -- ones that can handle the extra light and maintain efficiency?
      - philipkglass 10y ago
        Yes, there are different cell and cooling designs for low concentrating PV and high concentrating PV (LCPV, HCPV). But the price of non-concentrating PV systems has, so far, fallen fast enough to prevent either LCPV or HCPV from taking even 1% of the PV market. Soitec, Amonix, Suncore, and Sunfocus all failed to drum up enough CPV business to stay solvent.
      - jacquesm 10y ago
        Yes, but they're not cheap, in fact they are so expensive that it will be cheaper to cover the mirrors with cheaper cells directly... At this point in time there are no cheap and easy solutions in sight to make the next 2 to 5% gain in efficiency in a cost effective manner. But given enough time and effort I'm sure that that will happen, I expect the final cut-off to be somewhere around 25% net efficiency (solar incidence to electricity out of the system) for smaller installations and maybe up to 30% for much larger installations.
  - pjc50 10y ago
    That sounds like the "more economical" is wiped out as soon as you have a maintenance issue in the moving machinery. As it stands, maintenance-free panels are a huge advantage.
  - Tuna-Fish 10y ago
    Maintenance and installation costs already eclipse the panel costs. For any assembly you evaluate, you have to answer two questions: Will this require more complex installation than flat panels? Will this require more lifetime maintenance than flat panels? If the answer to either question is a yes, it doesn't matter how good your system is in any other measure, you will lose against simple flat panels in total cost per electricity produced for any small-scale installation.
    - jacquesm 10y ago
      Correct. I found this out the hard way with my two leafs of 2x4 panels tracking the sun in two axis. By the time the system was up and running I could have had more power and less headaches by installing 24 panels statically on the roof. It would have looked better too.
      - walrus01 10y ago
        Tracking systems with moving parts are expensive and complicated. With good quality 320W panels at $0.45/watt now in pallet quantities, going with a low cost fixed mounting system (whether ground or roof) makes much more economic sense. Considering the wind loading that a two axis tracking system which can hold 6x280W panels must endure, no wonder they cost a lot.
londons_explore 10y ago
Without them, multijunction cells are less efficient too. Leakage current, which happens even in darkness, wastes power at a fixed rate per unit area. By concentrating sunlight, one can generate far more than this leakage rate making it insignificant.

jacquesm 10y ago

> potentially That's the operative word here. And that is far from a run race with this particular technology, it is going to be close enough that it bears watching but not so good that it is a slam dunk winner.

nojvek 10y ago
To be honest it's a lot more economical to have cheap large mirrors on your roof directing sunlight towards a concentrated spot of PV cells of higher efficiency that are somewhat expensive. You could use some of that energy to have tiny motors that track the sunlight. This would net in more energy and less cost per square meter right?
- jacquesm 10y ago
  I've done a lot of experimenting with that. Here are some of the (surprising!) results: - you only need one motor to aim a whole array of mirrors if you're willing to make some exotic gears - the lifespan of the cells will shorten measurably - you will need to cool the cells if you don't want them to die very quickly - there will be a serious fire risk
  - ballenf 10y ago
    Are there cells designed for higher intensity than others -- ones that can handle the extra light and maintain efficiency?
    - philipkglass 10y ago
      Yes, there are different cell and cooling designs for low concentrating PV and high concentrating PV (LCPV, HCPV). But the price of non-concentrating PV systems has, so far, fallen fast enough to prevent either LCPV or HCPV from taking even 1% of the PV market. Soitec, Amonix, Suncore, and Sunfocus all failed to drum up enough CPV business to stay solvent.
    - jacquesm 10y ago
      Yes, but they're not cheap, in fact they are so expensive that it will be cheaper to cover the mirrors with cheaper cells directly... At this point in time there are no cheap and easy solutions in sight to make the next 2 to 5% gain in efficiency in a cost effective manner. But given enough time and effort I'm sure that that will happen, I expect the final cut-off to be somewhere around 25% net efficiency (solar incidence to electricity out of the system) for smaller installations and maybe up to 30% for much larger installations.
- pjc50 10y ago
  That sounds like the "more economical" is wiped out as soon as you have a maintenance issue in the moving machinery. As it stands, maintenance-free panels are a huge advantage.
- Tuna-Fish 10y ago
  Maintenance and installation costs already eclipse the panel costs. For any assembly you evaluate, you have to answer two questions: Will this require more complex installation than flat panels? Will this require more lifetime maintenance than flat panels? If the answer to either question is a yes, it doesn't matter how good your system is in any other measure, you will lose against simple flat panels in total cost per electricity produced for any small-scale installation.
  - jacquesm 10y ago
    Correct. I found this out the hard way with my two leafs of 2x4 panels tracking the sun in two axis. By the time the system was up and running I could have had more power and less headaches by installing 24 panels statically on the roof. It would have looked better too.
    - walrus01 10y ago
      Tracking systems with moving parts are expensive and complicated. With good quality 320W panels at $0.45/watt now in pallet quantities, going with a low cost fixed mounting system (whether ground or roof) makes much more economic sense. Considering the wind loading that a two axis tracking system which can hold 6x280W panels must endure, no wonder they cost a lot.

londons_explore 10y ago

Without them, multijunction cells are less efficient too. Leakage current, which happens even in darkness, wastes power at a fixed rate per unit area. By concentrating sunlight, one can generate far more than this leakage rate making it insignificant.