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Im in holidays in Malaysia and it is god damn hot. You cannot leave your hotel/car and go out. All this because of the sun.

I we were to capture all the heat (solar panels, ...) would this help make the Earth cooler / fight global warming ?

Edit : see one of my comments, I mean use the heat to conduct some endothermic reactions (e.g solar panel -> electricity -> electrolyte)

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  • $\begingroup$ @MAFIA36790: It's a physically answerable question and it will actually play a huge role in the use of solar energy in the future. $\endgroup$
    – CuriousOne
    Apr 15, 2016 at 6:08
  • $\begingroup$ @CuriousOne: That was my opinion; the rest would be decided by the community. $\endgroup$
    – user36790
    Apr 15, 2016 at 6:10
  • $\begingroup$ @CuriousOne to what stackexchange should I post ? I thought of Chemistry $\endgroup$
    – Thomas
    Apr 15, 2016 at 7:50
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    $\begingroup$ @CuriousOne: That is a physics question, and the answer (just for the record, you know this I'm sure!) is generally 'no': they capture some energy which then gets turned back into heat. They could only if we used them, for instance, to drive some chemical reaction uphill and then store the result. But that's probably implausible: making fuel in order to bury it seems unlikely! It's interesting to consider whether you could use solar power to sequester CO2 in some chemically good form: the answer is yes in theory, no in practice (the amount of energy you need is absurd). $\endgroup$
    – user107153
    Apr 15, 2016 at 10:16
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    $\begingroup$ @tfb: That's exactly what I meant by "thermodynamic Rube Goldberg machines". To go from electricity to chemistry and back is not a winning strategy. The question if one could use solar to locally cool the environment is not trivial, but it is good physics. I think we can identify the mechanisms here, even if we can't suggest working solutions, which would require a lot of detailed calculation. $\endgroup$
    – CuriousOne
    Apr 15, 2016 at 10:20

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There are several interacting effects.

And for global warming, we need to look at the whole earth.

First effect: putting the panels up may change the albedo - the reflectivity - of the surface. That will increase the amount of energy absorbed by the earth, rather than reflected into space. The effect would be a miniscule increase in heating.

Second effect: connecting the panels to the energy system means that renewable energy will be used, rather than fossil fuels being burnt. Which means that there will be less additional heat in the earth that would have come about from the burning of the fossil fuels. The effect would be a miniscule decrease in heating, of a very similar size to the first effect, but in the opposite direction.

Third effect: because less fossil fuels are burnt, less CO2 and methane would be released into the atmosphere. The effect would be a decrease in the heating of the Earth.

So, solar panels mitigate the increase in global warming, but the direct heat effects pretty much cancel each other out, and are dwarfed by the greenhouse-gas forcing effect.

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Solar panels are dark (they have to absorb light) and they do decrease the Earth's albedo, i.e. they make the planet locally darker. This means that locally they will cause slight additional heating. Part of the energy that a panel absorbs gets converted into electrical energy, which can be transferred off-site, i.e. removal of energy actually cools the panel. Currently used panels have peak a efficiency of about $20\%$, i.e. they will not be able to remove more than $20\%$ of the absorbed energy from their location, however, in the near future (i.e. within something like 20-30 years) we will have panels with $40\%$ or even higher efficiency, which means that large amounts of the absorbed energy can be transported off-site. Even more importantly, at night these panels can act as very efficient infra-red emitters and change the local air circulation patterns, which means that overall we may actually be able to get slight local cooling at and near large solar facilities.

None of this should be mistaken for global effects, though. The global problem is that for every kWh of energy that we are creating trough burning of fossil fuels, we are causing a $\mathrm{CO_2}$ loading of the atmosphere that creates a lasting multiple heating effect. The only way to reverse global warming is by undoing this heating. The most obvious way for that is by removing the $\mathrm{CO_2}$ from the atmosphere, again, which requires energy not created by fossil fuel burning. Since there is such a large multiplier on the primary cause of global warming, the same multiplier applies to no-carbon sources of energy. The direct local impact of solar panels is therefore dwarfed by their global impact.

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The energy budget of the earth is predominantly dependent on the balance between radiation coming from the sun ( there exists internal energy from the magma in the earth but it is a small percentage of the energy budget) and radiated energy from the earth back to space according to a modified black body radiation.

There is a secondary energy budget that can be calculated, between the atmosphere and the surface plus the surface radiating to space (part of the total budget). Solar panels are on the surface of the earth.

If we were to capture all the heat (solar panels, ...) would this help make the Earth cooler / fight global warming ?

Energy is conserved. In order to get cooler temperatures on the surface the surface energy budget should be controlled. Solar panels just move about 20% of the radiation energy falling on the surface to different parts on the surface. Only if the captured energy were radiated off the earth, for example by lasers pointing to space, would the energy budget of the surface change.

So the answer is for the normal usage of solar panels, no.

after question edit: Storing electricity into batteries would require an enormous amount of batteries, both expensive and finite in usage.

One could pump water up in mountains, to hydroelectric lakes . If one used the hydroelectric plants in the winter the extra energy would heat where it is released, and that is all to the good for winter. On a yearly basis the energy budget would remain the same. Only radiating energy off to space will change it.

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  • $\begingroup$ If you think of combustion in cars : oil is in the earth, when you burn it you change its state from liquid to gas. If we were to turn back gas into oil, energy is kept the same but the energy is "jailed" into other forms that reduce temperature. Is that correct ? $\endgroup$
    – Thomas
    Apr 15, 2016 at 7:53
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    $\begingroup$ @Thomas Yes, however note that the reason burning fossil fuels results in global warming is not the released heat energy, it's the carbon dioxide which alters the transfer of energy in the atmosphere. $\endgroup$
    – user107153
    Apr 15, 2016 at 10:09
  • $\begingroup$ @tfb Could you quantify/have you seen numbers that show that the heat produced is not so much compared to the greehouse effect ? $\endgroup$
    – Thomas
    Apr 15, 2016 at 10:56
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    $\begingroup$ @Thomas: Well, US human power use is about $10^{20}$ joules/year, which I think is about $0.3$ watts per square metre. If the average US temperature is $283$ kelvin then you can easily calculate the difference in temperature from all human power use: it's about a twentieth of a degree. That's from all human power use. $\endgroup$
    – user107153
    Apr 15, 2016 at 13:05
  • $\begingroup$ My answer replies to the specific question of solar panels which generate electricity. The energy would have to leave the surface in order to have an overall statistical cooling effect. As I said, lasers to space would do it, but it would be a foolish and expensive project. As for storing it in batteries, it would again be an expensive and finite end project, how many batteries can you have? $\endgroup$
    – anna v
    Apr 15, 2016 at 15:36

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