3 ms·

Not sure why I am responding since you moved the goal posts from operating efficiency to lifecycle efficiency but even there you are wrong. To your point re: l

Not sure why I am responding since you moved the goal posts from operating efficiency to lifecycle efficiency but even there you are wrong. To your point re: land use, this is why I said rooftop solar. The roof is already there, the structure is already there, there is zero additional land use and very little opportunity cost for the space. Further, the land use for coal is much broader than the plant area because of mining, transit, and waste heat management. There was a recent post on HN comparing total land usage by prime mover. Solar is only deadlier per unit than coal if you ignore substantial local health effects that aren’t priced in.[0] Your implied rate of degradation to go from 20-10 is more than 7%. Even 15-10 is more than 2.5% and again that is an absurd number that contradicts observed performance. You misunderstand what degradation means in this context, to your point. [0] https://surgery.duke.edu/news/despite-studies-health-effects-coal-burning-power-plants-remain-unknown https://surgery.duke.edu/news/despite-studies-health-effects...

arcticbull 4y ago
I never said anything about coal, and I updated the degradation numbers per your suggestion, but the degradation numbers themselves come from NREL. I think you're confusing the derating due to temperature with degradation. They are additive.
- dpierce9 4y ago
  Panel temps go up and down depending on time, date, location, and weather. On cool, sunny spring days you can see panels produce more than they are rated. You can’t simply apply a fixed worst-case derate for all time to all panels regardless of installation details. Further, the derates are not additive, they are multiplicative. (A a 20% panel which has degraded in lab efficiency by 10% operating at 90% thermal efficiency is running at 16.2% efficient compared to 18% for a non-degraded panel). Nothing you have said, however, addresses my first and principal point which is that operational efficiency has a different meaning for solar when compared to anything that has non-free inputs. Efficiency is outputs/inputs. One way to look at it is [energy out]/[energy hitting panel]. That is 20% for a solar plant, 45% for an nuclear analogue. Another, financial way is [value of output]/[cost of inputs]. This is infinity for solar setting aside fixed/financing costs and quite finite for nuclear using the same assumptions.
  - arcticbull 4y ago
    A device that's 15% efficient is inherently more wasteful than a device that's 100% efficient, right? Therefore we're wasting something. That thing isn't input fuel, it's the materials used to build the device, and manage its lifecycle. That doesn't mean it's free - it just means we're considering different inputs. Total efficiency here is the sum of all inputs over outputs. For solar panels that's land use, that's glass, silicon, plastic, PCBs, etc - in addition to the sun. Otherwise, in your model, a panel that's 100% efficient is inherently the same as one 15% efficient. In your model, a battery is infinitely efficient - after all it has no inputs, only outputs! Once you get to that point your model needs to be adjusted.
    - dpierce9 4y ago
      A nuclear plant that is 100% efficient would be better than the current ~40% units but it is thermodynamically impossible. Thanks Carnot. You are confusing operating/marginal efficiency with lifetime efficiency. Think about a power plant as a series of payments. You have one big up front payment to build the thing and a series of smaller payments to buy fuel and run it. For solar, those smaller payments are zero. There is still the fixed upfront payment and that is why you would prefer 40% efficient panels to 20% efficient panels everything else being equal. The marginal cost of rooftop solar is zero. Nothing is wasted. Really! No fuel is bought, the roof underneath is cooler and lasts longer, there are systemic benefits, etc. There is virtually no maintenance. No land is used (Solar land use is complicated but most places you can put solar wouldn’t support a nuclear plant). Light which would have bounced back into space or turned into infrared is instead made into usable, high grade energy. Land/build area that would otherwise do nothing is made useful. It is literally close to economic and physical magic. It is true that panels break, inverters die, upgrading is compelling, etc. However, most components are silicon, glass, copper, and aluminum. These are some of the most recyclable materials on earth. There are plenty of analyses of lifecycle energy and material costs and it is generally pretty favorable (1-2 year operating recovery time). The panels are warrantied in many cases for 25 years so idk where your 20 year then scrap lifespan comes from. Inverters tend to be the weaker link. Finally batteries have marginal round trip efficiency because what you put in doesn’t come back out 1-1 so I am not sure I follow your point.

arcticbull 4y ago

I never said anything about coal, and I updated the degradation numbers per your suggestion, but the degradation numbers themselves come from NREL. I think you're confusing the derating due to temperature with degradation. They are additive.

dpierce9 4y ago
Panel temps go up and down depending on time, date, location, and weather. On cool, sunny spring days you can see panels produce more than they are rated. You can’t simply apply a fixed worst-case derate for all time to all panels regardless of installation details. Further, the derates are not additive, they are multiplicative. (A a 20% panel which has degraded in lab efficiency by 10% operating at 90% thermal efficiency is running at 16.2% efficient compared to 18% for a non-degraded panel). Nothing you have said, however, addresses my first and principal point which is that operational efficiency has a different meaning for solar when compared to anything that has non-free inputs. Efficiency is outputs/inputs. One way to look at it is [energy out]/[energy hitting panel]. That is 20% for a solar plant, 45% for an nuclear analogue. Another, financial way is [value of output]/[cost of inputs]. This is infinity for solar setting aside fixed/financing costs and quite finite for nuclear using the same assumptions.
- arcticbull 4y ago
  A device that's 15% efficient is inherently more wasteful than a device that's 100% efficient, right? Therefore we're wasting something. That thing isn't input fuel, it's the materials used to build the device, and manage its lifecycle. That doesn't mean it's free - it just means we're considering different inputs. Total efficiency here is the sum of all inputs over outputs. For solar panels that's land use, that's glass, silicon, plastic, PCBs, etc - in addition to the sun. Otherwise, in your model, a panel that's 100% efficient is inherently the same as one 15% efficient. In your model, a battery is infinitely efficient - after all it has no inputs, only outputs! Once you get to that point your model needs to be adjusted.
  - dpierce9 4y ago
    A nuclear plant that is 100% efficient would be better than the current ~40% units but it is thermodynamically impossible. Thanks Carnot. You are confusing operating/marginal efficiency with lifetime efficiency. Think about a power plant as a series of payments. You have one big up front payment to build the thing and a series of smaller payments to buy fuel and run it. For solar, those smaller payments are zero. There is still the fixed upfront payment and that is why you would prefer 40% efficient panels to 20% efficient panels everything else being equal. The marginal cost of rooftop solar is zero. Nothing is wasted. Really! No fuel is bought, the roof underneath is cooler and lasts longer, there are systemic benefits, etc. There is virtually no maintenance. No land is used (Solar land use is complicated but most places you can put solar wouldn’t support a nuclear plant). Light which would have bounced back into space or turned into infrared is instead made into usable, high grade energy. Land/build area that would otherwise do nothing is made useful. It is literally close to economic and physical magic. It is true that panels break, inverters die, upgrading is compelling, etc. However, most components are silicon, glass, copper, and aluminum. These are some of the most recyclable materials on earth. There are plenty of analyses of lifecycle energy and material costs and it is generally pretty favorable (1-2 year operating recovery time). The panels are warrantied in many cases for 25 years so idk where your 20 year then scrap lifespan comes from. Inverters tend to be the weaker link. Finally batteries have marginal round trip efficiency because what you put in doesn’t come back out 1-1 so I am not sure I follow your point.