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> The PVs absorb a lot of thermal energy, too, more than the shingles themselves do. I've found this to be interesting going back as far as middle school, wher

> The PVs absorb a lot of thermal energy, too, more than the shingles themselves do. I've found this to be interesting going back as far as middle school, where we're taught renewable energy sources like solar panels can help reduce global warming by replacing greenhouse gas emitting alternatives. Yet fundamentally, they are designed to turn the only external source of energy our planet receives (sun light) into heat and other forms of energy that will eventually become heat rather than reflecting it back out into space (albeit through the atmosphere). Seems so backwards to me.

XorNot 4y ago
What do you think normally happens to the 1000w per square meter which the sun radiates?
- sacrosancty 4y ago
  More of it is reflect back into space from many natural surfaces than from solar panels. Not scientific but look how black this solar farm appears compared to the surrounding land https://eoimages.gsfc.nasa.gov/images/imagerecords/85000/85403/topaz_oli_2015002_lrg.jpg https://eoimages.gsfc.nasa.gov/images/imagerecords/85000/854...
  - XorNot 4y ago
    Right and so to follow this logic through, how do you think we get energy out of fossil fuels? Or nuclear reactors? Or a hypothetical fusion power plant?
    - sacrosancty 4y ago
      Steam turbines? What are you trying to say?
      - XorNot 4y ago
        > they are designed to turn the only external source of energy our planet receives (sun light) into heat and other forms of energy that will eventually become heat How does a steam turbine work? By heat: we burn things to get heat, and use steam to turn it into work which..turns it into heat. Your own statement is arguing against using energy in the first place, yet trying to frame it as a "renewable energy" problem as though the 60% of energy in gasoline isn't being thrown off into the environment, and 30-50% of energy in coal isn't the same, or as if literally every last bit of that - all of it because of the laws of thermodynamics - isn't eventually turned into heat. Total estimate energy consumption per year [1] is about 14420 TWh as of 2021. The total solar energy we would've received in that same year [2] is 1,515,480,000 TWh. Or 0.00095%. The amount of thermal emission from human activity on Earth is negligible. The idea that the amount of solar panels to power human civilization would have any non-local effect on the temperature of the planet is absurd. [1] https://en.wikipedia.org/wiki/World_energy_supply_and_consumption/energy/global-energy-consumption https://en.wikipedia.org/wiki/World_energy_supply_and_consum... [2] https://news.mit.edu/2011/energy-scale-part3-1026 https://news.mit.edu/2011/energy-scale-part3-1026
        sacrosancty 4y ago
        I wasn't arguing against the use of solar panels, just pointing out that they don't reflect light as much as the natural environment that would have been in their place. This whole discussion is purely academic because the proportion of earth covered by solar panels is negligible.
  - coryrc 4y ago
    I doubt that picture is recording most of the wavelengths of light responsible for getting heat back into space.
    - sacrosancty 4y ago
      It's mainly the visible wavelengths that can get through the atmosphere. You should see the absorption spectrum for water, it's remarkably transparent in the visible! That's how the greenhouse effect works - longer wavelength thermal radiation is blocked by greenhouse gasses.
      - coryrc 4y ago
        Visible light is also the ones turned into electricity, so it would make sense for panels to not be highly reflective at them.
        sacrosancty 4y ago
        Yes, that's why they're dark! But it doesn't change the fact that they're dark.
        petre 4y ago
        It also heats up dark surfaces. One way to remove that heat would be to have some kind of combined PV + solar thermal panel. The other lower tech option is to cover your roof with soil and plants, which release the heat back during the night. Vegetation is esentially a heat buffer.
mumblemumble 4y ago
One could argue that the only energy sources that aren't doing this somehow are geothermal and nuclear.
- stephen_g 4y ago
  That’s not correct - nuclear power plants only have efficiencies of about 33-37%, so 63 to 67% of the energy that nuclear reaction is producing is dumped into the atmosphere which wouldn’t have otherwise (obviously there would have otherwise still been some radioactive decay of the material in the ground if it wasn’t used as nuclear fuel, but nothing like refining it and bringing it to a critical mass in a reactor). Meanwhile, 100% of the energy that a solar panel receives (and radiates some back as heat) would have hit the earth anyway.
stormbrew 4y ago
The problem we're trying, broadly, to solve right now isn't "we're directly heating up the planet" but "we're trying to stop trapping heat in the atmosphere through a potentially self-propagating greenhouse process". This is why carbon neutrality is the focus and not just purely energy usage.
- grog454 4y ago
  It appears to be a different (and more direct) way of framing the same problem: https://www.nasa.gov/feature/langley/joint-nasa-noaa-study-finds-earths-energy-imbalance-has-doubled https://www.nasa.gov/feature/langley/joint-nasa-noaa-study-f... A better argument for solar panels is that per kwh of useful energy, a solar panel traps less solar energy (in kwh) than the CO2 produced by coal or gas or w/e. But I've never see this particular argument made and therefore couldn't even guess at HOW much better a solar panel is than coal and HOW much worse it is than nuclear or geothermal (which could actually be net energy loss for earth, by dispersing some thermal energy locked deep within the earth out to space).
  - deleted 4y ago
    [deleted]
  - stormbrew 4y ago
    > A better argument for solar panels is that per kwh of useful energy, a solar panel traps less solar energy (in kwh) than the CO2 produced by coal or gas or w/e. It's not a better argument because the solar panel doesn't "trap" the energy. At most it borrows it, eventually it will radiate back out if allowed to do so, just as it would if it were absorbed by a rock. Humans do not occupy enough of the surface of this planet to make a dent in that. The thing that will keep it from radiating back out is greenhouse gases in the atmosphere. And unlike some brief capture of energy, the greenhouse cycle is essentially a chain reaction.
    - MichaelZuo 4y ago
      But it is radiating it 'back out' less efficiently than a white roof. Thus black solar panels may indeed be a net negative if every building otherwise would have had a white roof. In a land of mostly dark roofs it's probably a net positive.
ericd 4y ago
Yeah, it’s a little counterintuitive, I’d just keep in mind that the amount of energy we use is tiny compared to the amount that the sun bombards the earth with. The absorption and generation is going to be insignificant compared to the amount trapped by the addutional greenhouse gasses.
stephen_g 4y ago
That doesn’t follow. Consider the alternatives - thermal generation (including nuclear) must reject massive amounts of waste heat into the atmosphere, before the electricity is used and heat is generated from that use. That’s what cooling towers are designed to do. That’s even before thinking about the effect from CO₂ or methane from gas fugitive emissions. The earth has the ability to radiate away quite considerable amounts of heat luckily, and solar produces considerably less waste heat than thermal. So solar and wind can only make things better. Minimising waste heat is of course good, which is why energy efficiency is so important, and heat pumps are doubly so - because they are extremely efficient, but also because they don’t produce as much heat but transfer most of it!

XorNot 4y ago

What do you think normally happens to the 1000w per square meter which the sun radiates?

sacrosancty 4y ago
More of it is reflect back into space from many natural surfaces than from solar panels. Not scientific but look how black this solar farm appears compared to the surrounding land https://eoimages.gsfc.nasa.gov/images/imagerecords/85000/85403/topaz_oli_2015002_lrg.jpg https://eoimages.gsfc.nasa.gov/images/imagerecords/85000/854...
- XorNot 4y ago
  Right and so to follow this logic through, how do you think we get energy out of fossil fuels? Or nuclear reactors? Or a hypothetical fusion power plant?
  - sacrosancty 4y ago
    Steam turbines? What are you trying to say?
    - XorNot 4y ago
      > they are designed to turn the only external source of energy our planet receives (sun light) into heat and other forms of energy that will eventually become heat How does a steam turbine work? By heat: we burn things to get heat, and use steam to turn it into work which..turns it into heat. Your own statement is arguing against using energy in the first place, yet trying to frame it as a "renewable energy" problem as though the 60% of energy in gasoline isn't being thrown off into the environment, and 30-50% of energy in coal isn't the same, or as if literally every last bit of that - all of it because of the laws of thermodynamics - isn't eventually turned into heat. Total estimate energy consumption per year [1] is about 14420 TWh as of 2021. The total solar energy we would've received in that same year [2] is 1,515,480,000 TWh. Or 0.00095%. The amount of thermal emission from human activity on Earth is negligible. The idea that the amount of solar panels to power human civilization would have any non-local effect on the temperature of the planet is absurd. [1] https://en.wikipedia.org/wiki/World_energy_supply_and_consumption/energy/global-energy-consumption https://en.wikipedia.org/wiki/World_energy_supply_and_consum... [2] https://news.mit.edu/2011/energy-scale-part3-1026 https://news.mit.edu/2011/energy-scale-part3-1026
      - sacrosancty 4y ago
        I wasn't arguing against the use of solar panels, just pointing out that they don't reflect light as much as the natural environment that would have been in their place. This whole discussion is purely academic because the proportion of earth covered by solar panels is negligible.
- coryrc 4y ago
  I doubt that picture is recording most of the wavelengths of light responsible for getting heat back into space.
  - sacrosancty 4y ago
    It's mainly the visible wavelengths that can get through the atmosphere. You should see the absorption spectrum for water, it's remarkably transparent in the visible! That's how the greenhouse effect works - longer wavelength thermal radiation is blocked by greenhouse gasses.
    - coryrc 4y ago
      Visible light is also the ones turned into electricity, so it would make sense for panels to not be highly reflective at them.
      - sacrosancty 4y ago
        Yes, that's why they're dark! But it doesn't change the fact that they're dark.
      - petre 4y ago
        It also heats up dark surfaces. One way to remove that heat would be to have some kind of combined PV + solar thermal panel. The other lower tech option is to cover your roof with soil and plants, which release the heat back during the night. Vegetation is esentially a heat buffer.

mumblemumble 4y ago

One could argue that the only energy sources that aren't doing this somehow are geothermal and nuclear.

stephen_g 4y ago
That’s not correct - nuclear power plants only have efficiencies of about 33-37%, so 63 to 67% of the energy that nuclear reaction is producing is dumped into the atmosphere which wouldn’t have otherwise (obviously there would have otherwise still been some radioactive decay of the material in the ground if it wasn’t used as nuclear fuel, but nothing like refining it and bringing it to a critical mass in a reactor). Meanwhile, 100% of the energy that a solar panel receives (and radiates some back as heat) would have hit the earth anyway.

stormbrew 4y ago

The problem we're trying, broadly, to solve right now isn't "we're directly heating up the planet" but "we're trying to stop trapping heat in the atmosphere through a potentially self-propagating greenhouse process". This is why carbon neutrality is the focus and not just purely energy usage.

grog454 4y ago
It appears to be a different (and more direct) way of framing the same problem: https://www.nasa.gov/feature/langley/joint-nasa-noaa-study-finds-earths-energy-imbalance-has-doubled https://www.nasa.gov/feature/langley/joint-nasa-noaa-study-f... A better argument for solar panels is that per kwh of useful energy, a solar panel traps less solar energy (in kwh) than the CO2 produced by coal or gas or w/e. But I've never see this particular argument made and therefore couldn't even guess at HOW much better a solar panel is than coal and HOW much worse it is than nuclear or geothermal (which could actually be net energy loss for earth, by dispersing some thermal energy locked deep within the earth out to space).
- deleted 4y ago
  [deleted]
- stormbrew 4y ago
  > A better argument for solar panels is that per kwh of useful energy, a solar panel traps less solar energy (in kwh) than the CO2 produced by coal or gas or w/e. It's not a better argument because the solar panel doesn't "trap" the energy. At most it borrows it, eventually it will radiate back out if allowed to do so, just as it would if it were absorbed by a rock. Humans do not occupy enough of the surface of this planet to make a dent in that. The thing that will keep it from radiating back out is greenhouse gases in the atmosphere. And unlike some brief capture of energy, the greenhouse cycle is essentially a chain reaction.
  - MichaelZuo 4y ago
    But it is radiating it 'back out' less efficiently than a white roof. Thus black solar panels may indeed be a net negative if every building otherwise would have had a white roof. In a land of mostly dark roofs it's probably a net positive.

ericd 4y ago

Yeah, it’s a little counterintuitive, I’d just keep in mind that the amount of energy we use is tiny compared to the amount that the sun bombards the earth with. The absorption and generation is going to be insignificant compared to the amount trapped by the addutional greenhouse gasses.

stephen_g 4y ago

That doesn’t follow. Consider the alternatives - thermal generation (including nuclear) must reject massive amounts of waste heat into the atmosphere, before the electricity is used and heat is generated from that use. That’s what cooling towers are designed to do. That’s even before thinking about the effect from CO₂ or methane from gas fugitive emissions. The earth has the ability to radiate away quite considerable amounts of heat luckily, and solar produces considerably less waste heat than thermal. So solar and wind can only make things better. Minimising waste heat is of course good, which is why energy efficiency is so important, and heat pumps are doubly so - because they are extremely efficient, but also because they don’t produce as much heat but transfer most of it!