4 ms·

Only half of our 500M square kilometre planet faces The Sun at any one time, and only half the surface (barren land and, more likely, oceans) could be used for

by heads 3y ago

Only half of our 500M square kilometre planet faces The Sun at any one time, and only half the surface (barren land and, more likely, oceans) could be used for solar panels. That gives us 125km2 of usable area. The atmosphere attenuates our 1300W/m2 of solar energy down to 300W/m2 so for a 125M km2 planet you only get 40PW of available power, or 5PW after 80% loss in solar panels and distribution. In terms of global energy demand we’re currently using 25PWh per year which is the equivalent of 3TW. Assuming oil runs out, politics annuls nuclear options, and we cover most of the planet in solar panels then peak terrestrial solar is three orders of magnitude away. Covering over everything with panels would presumably have devastating effects on the environment just as much as fossil fuels but if we limit to 1% coverage then we’re only one order of magnitude away from terrestrial solar being unable to power the world. It’s neither sunny nor midday all the time either so solar is starting to look dangerously close to not cutting it, and yet harvesting solar energy could be our only option for power for the next ten thousand years. I pulled all these numbers from Wikipedia and crunched them with GNU units — this is HN after all — but it doesn’t sound unreasonable to conclude that anything planet bound is going to be bounded by planet size. Moreover, if the goal is for power generation to have zero impact on our biome then we should probably not generate power within the biome itself.

CorrectHorseBat 3y ago
On that scale simply using power on earth will have a devastating impact on the environment and microwaving more power in makes it even worse.
- heads 3y ago
  Yes and this goes into some awkward Thanos did nothing wrong territory. I’m sure there’s serious research out there on what the fundamental population limit of Earth should be if we are to bound it based on minimal ecological impact.
  - hiddencost 3y ago
    "Malthus" is taught in high school. The idea comes up all over intellectual history and has yet to pan out. One of these days.
    - ben_w 3y ago
      What's taught in high school is generally simplified to the point of falsehood. What Malthus wrote about was basically the lived experiences of those around him for basically all of what he knew of to be recorded history: improved farming meant more people, not happier people. Now, I'm not qualified to even judge if Jared Diamond's even fair let alone correct, but he wrote in Collapse (2005) that the Rwandan Genocide was brought about in part due to excessive population pressures, that it "illustrates a case where Malthus's worst-case scenario does seem to have been right." On the other hand, it also seems plausible to me that widespread access to contraceptives may break the assumptions behind Malthus.
      - CorrectHorseBat 3y ago
        May? All developed countries have subreplacement fertility [1] (and falling) the world population is predicted to peak before the end of the century. https://en.m.wikipedia.org/wiki/Sub-replacement_fertility https://en.m.wikipedia.org/wiki/Sub-replacement_fertility
        ben_w 3y ago
        For now, yes; there is also a distinct possibility that the sub-populations who have more kids do so because of some genetic tendency (singular or plural) which would, if it actually exists and isn't mere hypothetical, rapidly reverse this.
  - ben_w 3y ago
    There probably is such research, but "minimum ecological impact" is highly subjective and technology dependent. We had some impact as hunter-gatherers at 10M population, probably made some species extinct from hunting. If I assumed c. 1940 tech was the limit and wanted to minimise human ecological impact, this population would be the maximum sustainable given CO2 emissions. Conversely, if we put submarine cities in deep water, powered by PV on the surface that are ready to withdraw when storms come[0] and feed ourselves on the most efficient foods we already know how to grow in sealed environments, we could probably support trillions of people… but at that level we might possibly need to find some asteroids rich in, IDK, phosphorus or something. I have seen larger maximum population numbers, but they're for scenarios where you fairly strongly disregard the ecology — if you're willing to do weird stuff like putting up an L1 sun shade to block wavelengths of sunlight that serve only to heat us up because they get fully absorbed by the atmosphere, but somewhere in the 10-100 trillion range our direct heat emissions become dominant. [0] ignore the expense, this is a thought experiment
  - jacquesm 3y ago
    > I’m sure there’s serious research out there on what the fundamental population limit of Earth should be if we are to bound it based on minimal ecological impact. There is but there is a 7/8ths probability that you're not going to like the answer. https://en.wikipedia.org/wiki/Sustainable_population https://en.wikipedia.org/wiki/Sustainable_population
stevage 3y ago
>Moreover, if the goal is for power generation to have zero impact on our biome I don't know if it is. The impacts could be positive, or at least counteract other negative impacts. For instance, shading some ocean might counteract the heating of it.
- readyplayernull 3y ago
  But would kill light dependent life and increase some bacterial and fungi populations that might not be healthy for animals.
- sandworm101 3y ago
  Oceans are where co2 is turned into oxygen. We really dont want to be deliberately hampering that cycle. Put the panels on land, preferably atop sand or bare rock.
  - ben_w 3y ago
    Primary production is mostly concentrated in the costal regions. The following map's colour bands are on a log scale: https://upload.wikimedia.org/wikipedia/commons/4/44/Seawifs_global_biosphere.jpg https://upload.wikimedia.org/wikipedia/commons/4/44/Seawifs_... There's other reasons not to put PV in the middle of the oceans, like the storms, and that if you're willing to make suitable transmission lines of that kind of distance, you can also perfectly well connect the Nevada and Namib deserts and put panels in each so the time zones are powering each other after sunset/before sunrise).
tails4e 3y ago
Does beaming power to earth change the energy in the system? At least with solar all energy was already being absorbed by the earth's atmosphere, just being converted to another form and ultimately back to heat. By beaming energy that would not otherwise have passed through the atmosphere we are effectively warming the planet. Though I've no idea if the number is material or not.
jacquesm 3y ago
> Only half of our 500M square kilometre planet faces The Sun at any one time, and only half the surface (barren land and, more likely, oceans) could be used for solar panels. That gives us 125km2 of usable area. You're off by a factor of 1,000.
- heads 3y ago
  By a factor of a million in my typo of “125M km2”, right? The available solar power calculation is still correct, I believe.
  - ben_w 3y ago
    > The atmosphere attenuates our 1300W/m2 of solar energy down to 300W/m2 so for a 125M km2 planet you only get 40PW of available power, or 5PW after 80% loss in solar panels and distribution. I think you've got a mistake and a bad assumption here, too. I think the atmosphere attenuates by not to 300W/m^2, but you might also mean that the earth being spherical rather than flat geometrically reduces the solar irradiation to an annual average of 340W/m^2? But then you'd be double-counting the effect of night, and ignoring weather. The currently installed PV systems produce about 10% of their nameplate capacity, so I tend to just use that in my approximations of all the different effects together, so a 20% efficient cell[0] would produce 1kW/m^2 * 10% (capacity factor) * 20% (efficiency) gets 20 W/m^2 in practice. 1% of land with those percentages gets us 29.79 TW[1] which is indeed only about 1 order of magnitude away from current use (and we definitely want to use more energy than we do as most people don't have the luxury of energy abundance found in developed nations), but that already accounts for it being "neither sunny nor midday all the time either". But also, 1% of Earth's land area is already built up[2], so I think this may be too tight a constraint (after all, PV can be used as a surface covering for buildings and even vehicles). With sufficient political will (yes yes, I know that's wishful thinking), it's not unreasonable to build a thick enough set of conductors to make even a global power grid have negligible resistance — you'd need a 1m^2 cross section for an equatorial ring of aluminium[3] to have 1Ω resistance, and while this would be a big project today, it's not so large as to be absurd for a decade-long project. [0] The record for efficiency is 47.6%, though this will only matter if we ever ran out of land: https://en.wikipedia.org/wiki/Solar-cell_efficiency https://en.wikipedia.org/wiki/Solar-cell_efficiency [1] https://www.wolframalpha.com/input?i=land+area+on+earth+*+1%25+*+20W%2Fm%5E2 https://www.wolframalpha.com/input?i=land+area+on+earth+*+1%... [2] https://ourworldindata.org/land-use https://ourworldindata.org/land-use [3] Don't put 20 TW through a single ring. If I did the maths right, the magnetic field at the surface will be in the order of 1 tesla depending on how you choose to distribute current and voltage. Also, I have no idea how much energy such a thing would absorb from a CME, but I think the big CMEs can be in the range of 5e25 J, and if that's efficiently absorbed it would vaporise even a ring that big.

by heads 3y ago

CorrectHorseBat 3y ago

On that scale simply using power on earth will have a devastating impact on the environment and microwaving more power in makes it even worse.

heads 3y ago
Yes and this goes into some awkward Thanos did nothing wrong territory. I’m sure there’s serious research out there on what the fundamental population limit of Earth should be if we are to bound it based on minimal ecological impact.
- hiddencost 3y ago
  "Malthus" is taught in high school. The idea comes up all over intellectual history and has yet to pan out. One of these days.
  - ben_w 3y ago
    What's taught in high school is generally simplified to the point of falsehood. What Malthus wrote about was basically the lived experiences of those around him for basically all of what he knew of to be recorded history: improved farming meant more people, not happier people. Now, I'm not qualified to even judge if Jared Diamond's even fair let alone correct, but he wrote in Collapse (2005) that the Rwandan Genocide was brought about in part due to excessive population pressures, that it "illustrates a case where Malthus's worst-case scenario does seem to have been right." On the other hand, it also seems plausible to me that widespread access to contraceptives may break the assumptions behind Malthus.
    - CorrectHorseBat 3y ago
      May? All developed countries have subreplacement fertility [1] (and falling) the world population is predicted to peak before the end of the century. https://en.m.wikipedia.org/wiki/Sub-replacement_fertility https://en.m.wikipedia.org/wiki/Sub-replacement_fertility
      - ben_w 3y ago
        For now, yes; there is also a distinct possibility that the sub-populations who have more kids do so because of some genetic tendency (singular or plural) which would, if it actually exists and isn't mere hypothetical, rapidly reverse this.
- ben_w 3y ago
  There probably is such research, but "minimum ecological impact" is highly subjective and technology dependent. We had some impact as hunter-gatherers at 10M population, probably made some species extinct from hunting. If I assumed c. 1940 tech was the limit and wanted to minimise human ecological impact, this population would be the maximum sustainable given CO2 emissions. Conversely, if we put submarine cities in deep water, powered by PV on the surface that are ready to withdraw when storms come[0] and feed ourselves on the most efficient foods we already know how to grow in sealed environments, we could probably support trillions of people… but at that level we might possibly need to find some asteroids rich in, IDK, phosphorus or something. I have seen larger maximum population numbers, but they're for scenarios where you fairly strongly disregard the ecology — if you're willing to do weird stuff like putting up an L1 sun shade to block wavelengths of sunlight that serve only to heat us up because they get fully absorbed by the atmosphere, but somewhere in the 10-100 trillion range our direct heat emissions become dominant. [0] ignore the expense, this is a thought experiment
- jacquesm 3y ago
  > I’m sure there’s serious research out there on what the fundamental population limit of Earth should be if we are to bound it based on minimal ecological impact. There is but there is a 7/8ths probability that you're not going to like the answer. https://en.wikipedia.org/wiki/Sustainable_population https://en.wikipedia.org/wiki/Sustainable_population

stevage 3y ago

>Moreover, if the goal is for power generation to have zero impact on our biome I don't know if it is. The impacts could be positive, or at least counteract other negative impacts. For instance, shading some ocean might counteract the heating of it.

readyplayernull 3y ago
But would kill light dependent life and increase some bacterial and fungi populations that might not be healthy for animals.
sandworm101 3y ago
Oceans are where co2 is turned into oxygen. We really dont want to be deliberately hampering that cycle. Put the panels on land, preferably atop sand or bare rock.
- ben_w 3y ago
  Primary production is mostly concentrated in the costal regions. The following map's colour bands are on a log scale: https://upload.wikimedia.org/wikipedia/commons/4/44/Seawifs_global_biosphere.jpg https://upload.wikimedia.org/wikipedia/commons/4/44/Seawifs_... There's other reasons not to put PV in the middle of the oceans, like the storms, and that if you're willing to make suitable transmission lines of that kind of distance, you can also perfectly well connect the Nevada and Namib deserts and put panels in each so the time zones are powering each other after sunset/before sunrise).

tails4e 3y ago

Does beaming power to earth change the energy in the system? At least with solar all energy was already being absorbed by the earth's atmosphere, just being converted to another form and ultimately back to heat. By beaming energy that would not otherwise have passed through the atmosphere we are effectively warming the planet. Though I've no idea if the number is material or not.

jacquesm 3y ago

> Only half of our 500M square kilometre planet faces The Sun at any one time, and only half the surface (barren land and, more likely, oceans) could be used for solar panels. That gives us 125km2 of usable area. You're off by a factor of 1,000.

heads 3y ago
By a factor of a million in my typo of “125M km2”, right? The available solar power calculation is still correct, I believe.
- ben_w 3y ago
  > The atmosphere attenuates our 1300W/m2 of solar energy down to 300W/m2 so for a 125M km2 planet you only get 40PW of available power, or 5PW after 80% loss in solar panels and distribution. I think you've got a mistake and a bad assumption here, too. I think the atmosphere attenuates by not to 300W/m^2, but you might also mean that the earth being spherical rather than flat geometrically reduces the solar irradiation to an annual average of 340W/m^2? But then you'd be double-counting the effect of night, and ignoring weather. The currently installed PV systems produce about 10% of their nameplate capacity, so I tend to just use that in my approximations of all the different effects together, so a 20% efficient cell[0] would produce 1kW/m^2 * 10% (capacity factor) * 20% (efficiency) gets 20 W/m^2 in practice. 1% of land with those percentages gets us 29.79 TW[1] which is indeed only about 1 order of magnitude away from current use (and we definitely want to use more energy than we do as most people don't have the luxury of energy abundance found in developed nations), but that already accounts for it being "neither sunny nor midday all the time either". But also, 1% of Earth's land area is already built up[2], so I think this may be too tight a constraint (after all, PV can be used as a surface covering for buildings and even vehicles). With sufficient political will (yes yes, I know that's wishful thinking), it's not unreasonable to build a thick enough set of conductors to make even a global power grid have negligible resistance — you'd need a 1m^2 cross section for an equatorial ring of aluminium[3] to have 1Ω resistance, and while this would be a big project today, it's not so large as to be absurd for a decade-long project. [0] The record for efficiency is 47.6%, though this will only matter if we ever ran out of land: https://en.wikipedia.org/wiki/Solar-cell_efficiency https://en.wikipedia.org/wiki/Solar-cell_efficiency [1] https://www.wolframalpha.com/input?i=land+area+on+earth+*+1%25+*+20W%2Fm%5E2 https://www.wolframalpha.com/input?i=land+area+on+earth+*+1%... [2] https://ourworldindata.org/land-use https://ourworldindata.org/land-use [3] Don't put 20 TW through a single ring. If I did the maths right, the magnetic field at the surface will be in the order of 1 tesla depending on how you choose to distribute current and voltage. Also, I have no idea how much energy such a thing would absorb from a CME, but I think the big CMEs can be in the range of 5e25 J, and if that's efficiently absorbed it would vaporise even a ring that big.