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>"The only figure of merit in a PV system is cost per kilowatt-hour installed". This doesn't make intuitive sense to me. If you could pay $50 for a bucket of

>"The only figure of merit in a PV system is cost per kilowatt-hour installed". This doesn't make intuitive sense to me. If you could pay $50 for a bucket of goop you can slather on your roof that would capture 1% of the incident light energy hitting it forever, would everyone do so? by your standard "hell yeah" as that means the equivalent of $2.5k per roof (I multiplied the $50 for 1% by 50 to conpare apples to apples) to capture 50% of the energy which is far better $ per KWh than offered by anyone else! The issue is that for many people they would prefer to capture more than 1% and they are willing to pay more per kwh in exchange for getting more kilowatt hrs. So they would prefer to pay a large premium, thereby showing that it really doesn't just come down to cost per KW-hr installed. there are other factors.

sbierwagen 9y ago
I'm a little confused by your argument, so I'll go through it one clause at a time. If you could pay $50 for a bucket of goop you can slather on your roof that would capture 1% of the incident light energy hitting it forever, would everyone do so? Sure? If you postulate a PV system that has much lower cost per KWh installed than has ever been achieved, then of course it'll make economic sense. by your standard "hell yeah" as that means the equivalent of $2.5k per roof (I multiplied the $50 for 1% by 50 to conpare apples to apples) to capture 50% of the energy which is far better $ per KWh than offered by anyone else! Sure? You made the fictional system way, way better, so it's an even better deal now. The issue is that for many people they would prefer to capture more than 1% and they are willing to pay more per kwh in exchange for getting more kilowatt hrs. So they would prefer to pay a large premium, thereby showing that it really doesn't just come down to cost per KW-hr installed. You are now talking about something completely different. Homeowners demonstrably don't care about the power conversion efficiency of their roof-- the penetration rate of rooftop solar is pathetic. People care about how much their electricity costs, and only install rooftop solar if gives them cheaper electricity. If grid power costs $0.10/KWh, and solar costs $0.50/KWh, then they won't buy it. Look out the window! Look at all the solar panels you don't see. That's the argument from economics. The argument from product availability: regular planar unconcentrated multijunction cells for terrestrial use don't exist. You can't buy them, because there's no market for a $10,000 500 watt cell when $200 300 watt cells are sold. https://www.wholesalesolar.com/solar-panels https://www.wholesalesolar.com/solar-panels You can get them for space applications, presumably at incredible expense: http://www.spectrolab.com/DataSheets/Panel/panels.pdf http://www.spectrolab.com/DataSheets/Panel/panels.pdf Concentrated multijunction panels for terrestrial use exist, but are only used in utility-scale installations, since you don't do two-axis tracking with rooftop solar. (Dual tracked solar panels cast shadows on each other, so they have to be spaced much farther apart, and consequently have bad space utilization) The only figure of merit in a PV system is cost per kilowatt-hour installed. Right now, all rooftop solar installations are single-junction. If multijunction cells resulted in a lower cost per kilowatt-hour installed, then they would be used, but they don't, so they aren't.
- logicallee 9y ago
  I'm really confused why you don't follow my argument. Suppose instead of $50 for a 1% efficient goop, my goop only cost $1 but was only 0.1% efficient. That is five times more efficient per dollar but reduces your yield by 10x! Do you see why nobody who wanted any appreciable amount of solar energy would put my "$1 for a roof's worth of 0.1% efficient solar collection" on their roof? They would naturally choose the "$50 for a roof's worth of 1% efficient solar collection" goop over that one (if those two were the only two choices), even though it's 5x worse per kilowatt-hour? I hope this explains what I'm talking about. A lot of people want more than 0.1% efficiency because they'd like to collect more energy than that...
  - sbierwagen 9y ago
    I follow your argument, I just don't think it matches reality. In any system analysis, you have to consider all the relevant factors. If you wave away important factors for the sake of argument, you get the wrong answers, and end up in long arguments on internet forums, repeating yourself a lot. Let's game out some scenarios using your numbers. The choices are between a $1 array that gives 100 watt-hours, ($0.01/Wh) or a $50 array that gives 1000 watt-hours. ($0.05/Wh) Rooftop solar, grid power is $0.001/Wh: You don't buy either array, since neither is cheaper than grid. This is true for most of the industrialized world. Rooftop solar, grid power is $0.025/Wh: You buy the 100 watt-hour array, since the power it produces is cheaper than grid power. You don't care about total wattage, since you can get all the watts you want from the grid. This is true of places where either electricity is expensive, or PV is subsidized. (Hawaii, Germany, etc) Rooftop solar, grid power is $0.1/Wh: You do buy the 1000 watt-hour array, since it saves you from having to buy expensive grid watt-hours. There is no place on Earth where grid power is more expensive than both single-crystal and multijunction PV. Rooftop solar, offgrid: Here you do strongly care about array output... but you're only offgrid in very rural locations, where land is cheap. In practice, off grid solar is never limited to just rooftops! If you need more watt-hours, you build bigger arrays, rather than paying five times as much per panel. Space: You need every milliwatthour, and each gram of spacecraft costs hundreds of dollars anyway, so multijunction PV suddenly becomes price competitive.

sbierwagen 9y ago

I'm a little confused by your argument, so I'll go through it one clause at a time. If you could pay $50 for a bucket of goop you can slather on your roof that would capture 1% of the incident light energy hitting it forever, would everyone do so? Sure? If you postulate a PV system that has much lower cost per KWh installed than has ever been achieved, then of course it'll make economic sense. by your standard "hell yeah" as that means the equivalent of $2.5k per roof (I multiplied the $50 for 1% by 50 to conpare apples to apples) to capture 50% of the energy which is far better $ per KWh than offered by anyone else! Sure? You made the fictional system way, way better, so it's an even better deal now. The issue is that for many people they would prefer to capture more than 1% and they are willing to pay more per kwh in exchange for getting more kilowatt hrs. So they would prefer to pay a large premium, thereby showing that it really doesn't just come down to cost per KW-hr installed. You are now talking about something completely different. Homeowners demonstrably don't care about the power conversion efficiency of their roof-- the penetration rate of rooftop solar is pathetic. People care about how much their electricity costs, and only install rooftop solar if gives them cheaper electricity. If grid power costs $0.10/KWh, and solar costs $0.50/KWh, then they won't buy it. Look out the window! Look at all the solar panels you don't see. That's the argument from economics. The argument from product availability: regular planar unconcentrated multijunction cells for terrestrial use don't exist. You can't buy them, because there's no market for a $10,000 500 watt cell when $200 300 watt cells are sold. https://www.wholesalesolar.com/solar-panels https://www.wholesalesolar.com/solar-panels You can get them for space applications, presumably at incredible expense: http://www.spectrolab.com/DataSheets/Panel/panels.pdf http://www.spectrolab.com/DataSheets/Panel/panels.pdf Concentrated multijunction panels for terrestrial use exist, but are only used in utility-scale installations, since you don't do two-axis tracking with rooftop solar. (Dual tracked solar panels cast shadows on each other, so they have to be spaced much farther apart, and consequently have bad space utilization) The only figure of merit in a PV system is cost per kilowatt-hour installed. Right now, all rooftop solar installations are single-junction. If multijunction cells resulted in a lower cost per kilowatt-hour installed, then they would be used, but they don't, so they aren't.

logicallee 9y ago
I'm really confused why you don't follow my argument. Suppose instead of $50 for a 1% efficient goop, my goop only cost $1 but was only 0.1% efficient. That is five times more efficient per dollar but reduces your yield by 10x! Do you see why nobody who wanted any appreciable amount of solar energy would put my "$1 for a roof's worth of 0.1% efficient solar collection" on their roof? They would naturally choose the "$50 for a roof's worth of 1% efficient solar collection" goop over that one (if those two were the only two choices), even though it's 5x worse per kilowatt-hour? I hope this explains what I'm talking about. A lot of people want more than 0.1% efficiency because they'd like to collect more energy than that...
- sbierwagen 9y ago
  I follow your argument, I just don't think it matches reality. In any system analysis, you have to consider all the relevant factors. If you wave away important factors for the sake of argument, you get the wrong answers, and end up in long arguments on internet forums, repeating yourself a lot. Let's game out some scenarios using your numbers. The choices are between a $1 array that gives 100 watt-hours, ($0.01/Wh) or a $50 array that gives 1000 watt-hours. ($0.05/Wh) Rooftop solar, grid power is $0.001/Wh: You don't buy either array, since neither is cheaper than grid. This is true for most of the industrialized world. Rooftop solar, grid power is $0.025/Wh: You buy the 100 watt-hour array, since the power it produces is cheaper than grid power. You don't care about total wattage, since you can get all the watts you want from the grid. This is true of places where either electricity is expensive, or PV is subsidized. (Hawaii, Germany, etc) Rooftop solar, grid power is $0.1/Wh: You do buy the 1000 watt-hour array, since it saves you from having to buy expensive grid watt-hours. There is no place on Earth where grid power is more expensive than both single-crystal and multijunction PV. Rooftop solar, offgrid: Here you do strongly care about array output... but you're only offgrid in very rural locations, where land is cheap. In practice, off grid solar is never limited to just rooftops! If you need more watt-hours, you build bigger arrays, rather than paying five times as much per panel. Space: You need every milliwatthour, and each gram of spacecraft costs hundreds of dollars anyway, so multijunction PV suddenly becomes price competitive.