- cross-posted to:
- earthscience
- cross-posted to:
- earthscience
TL;DR
using/generating energy always emits heat as waste and there is an upper limit of efficiency that we are not that far from. if that energy was generated via something that is not a natural heat gradient for the earth’s surface there is a net increase of heat in the earth system simply by generating and using energy.
a lot of energy sources fall into this: fossil fuel, nuclear, geothermal, etc. two that don’t are (certain types of) solar and wind, since their energy would eventually be dissipated onto earth’s surface whether we intercept or not.
that waste heat is currently estimated to be ~2% of the heating power caused by global warming, so already significant. we essentially have an upper limit on sustainable energy usage on earth (and therefore an avg per person usage) or we will have Global Warming 2: Waste Heat Boogaloo.
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Waste heat is only about 1/100,000 of the warming we get from burning fossil fuels. It won’t really become significant unless we use a nuclear-heavy approach to decarbonization.
thanks for the article. it seems that number only accounts for the heat released during energy generation at the power plant but there is also significant heat waste when it’s consumed. AC units, electric heaters, refrigerators, lightbulbs, pumps, basically all other machines. an individual unit might not produce that much but there are billions of them.
That doesn’t really change the picture much. A typical coal-burning power plant turns about 1/3 of the energy in the coal into electricity. Highly-efficient combined cycle gas turbines might turn 60% of the energy in the gas into electricity. That energy is the amount of waste heat that those devices produce.
turbines are still energy generation, heat is also emitted when that produced electricity is consumed.
- about 15% of electricity the world produces is used for refrigeration
- about 20% of electricity the world produces is used for computers
all machines have efficiency < 1 and therefore emit heat when used. many of those machines even have the goal of producing/moving heat.
all machines have efficiency < 1 and therefore emit heat when used.
All machines produce heat equal to their energy input. They have an efficiency of 1.0 at producing heat. Some will store it in potential energy for some period, but unless that reaction was exothermic, that potential energy will itself be released and fall back to a lower energy level, usually releasing it as heat.
Yes, but the amount of heat they’re generating is by definition no more than the amount of energy in the electricity. This caps the total waste heat impact, and means that for fossil-fuel-generated-electricity, their impact on the earth’s temperature is almost entirely a result of warming caused by the greenhouse gases emitted.
There is an EXCELLENT physics text book freely available that focuses on the physics of energy sources: https://escholarship.org/uc/item/9js5291m
It’s by Tom Murphy of “Do the Math” fame. Basically, unlimited perpetual growth runs afoul of basic physical limitations in shockingly short timeframes.
Very interesting read, thanks for sharing. I particularly liked the part about the origin of the energy we use and wheter that energy would have heated the planet anyway. Carbon trapped in fossil fuel comes from the sun and would have heated the planet during the Carboniferous. By burning it, we “import” heat from this era. Nuclear fission is “importing” heat from the supernovae that seeded the solar system. However, is geothermal “importing” remnant heat of the solar system’s creation, as material collapsed in the Earth’s gravity well? The heat from the center of the planet would have traveled to the surface eventually, but it would have taken much longer. Maybe we are “importing” heat from the future instead of the past in this case.
There are two things he didn’t mention that seem relevant to me. Firstly, that entropy can go down locally. Of course it always rises in a closed system, but the Earth surface is not a closed system. Life, an incredibly organized machine risen from just photosynthesis or chemosynthesis, is an exceptional example of entropy locally decreasing because of external influx of energy from the Sun and the center of the Earth.
Secondly, he justly warned about gathering energy from outer space and importing in on Earth, something that I had never considered. But what if we used this energy in outer space as well? This seems like a good motivation for space colonization. That’s a (probably foolish) dream that could be compatible with exponential growth beyond what is available on Earth.
That’s a (probably foolish) dream that could be compatible with exponential growth beyond what is available on Earth.
Sounds like a Solarpunk novel to be written. Let’s put all incineration activities away. Yet, space colonization is here and serves capital accumulation, first and foremost. There’s also the tiny part where rockets have to be shot to outer space with a little bit of energy and waste heat.
but the Earth surface is not a closed system. Life, an incredibly organized machine risen from just photosynthesis or chemosynthesis, is an exceptional example of entropy locally decreasing because of external influx of energy from the Sun and the center of the Earth.
yeah, my understanding of this is the earth’s surface is generally at an energy equilibrium (combining sunlight, geothermal heat, dissipation to space, etc) which results in the current climate. adding energy to that system via heat changes that equilibrium.
Secondly, he justly warned about gathering energy from outer space and importing in on Earth, something that I had never considered. But what if we used this energy in outer space as well? This seems like a good motivation for space colonization. That’s a (probably foolish) dream that could be compatible with exponential growth beyond what is available on Earth.
wow this is an incredible idea! we could easily use all the energy we want in space or on another body that is less sensitive to heat (moon, mars, etc)
Solution: use heat pumps to heat homes.
