If heat is energy, why isn’t it possible to genereate electricity out of thin (warm) air and by that cooling our atmosphere while generating (nearly) endless energy?
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When you convert heat to energy, you need a difference in heat. Heat engines work when something loses heat, and that heat is converted into work – for example, you use a heat source to boil water, and then use the steam from that boiled water to turn a turbine (which is how a steam engine works)
With ambient air, there’s no difference in heat. The only way that warm air will cool down is if you bring it into contact with something cold, like an air conditioner – but that requires doing some work to cool the air down.
Energy naturally flows “downhill” – a hot object will dump heat into a cold object, but the reverse will never happen.
If you have hot air and want to extract energy from it, you need to provide a lower energy place for the energy to flow.
There is no low energy place available to do this. The inside of the earth is even hotter, and the cold vacuum of space is gravitationally unfavorable and too far away.
Imagine heat as being like a river. It has energy and you can do something with it. But you can’t just take a river, get energy, and make the river disappear. You need to have something like a waterfall, water going from a high place, to a low place, and you put your energy-extracting machine in the middle.
In the case of heat, you absolutely can extract energy, but you can’t just take the energy and make the heat disappear. You would need a place of high heat and a place of low heat and move the heat from high to low. In between the two you place your energy extracting machine and that’s how you’d get energy.
So in the case of heat in the atmosphere, to get energy out you’d need a place of “cold atmosphere” and get the heat to flow between them.
Do some googling on a “carnot engine”, that’s the physics behind what I’m talking about.
In short, in order to get energy from heat you need a hot place, and a cold place, and the amount of energy you get is related to the different in temperatures. If everything is a single temperature you’d get 0 energy out. If you had a source of infinite hot and a source of infinite cold you could create the “most efficient engine” physically possible. Every real engine in existence falls somewhere between the two.
Even if we took heat out of the air and used it to generate electricity, all that energy in the electricity ends up as heat again.
As for why we can’t just generate electricity out of nowhere? That’s thermodynamics 2nd law. It basically says that energy will diffuse over time. If you have an area with lots of energy and an area with low energy, over time they will even out in energy. Just like your hot cup of coffee becomes room temperature over time. The inverse is not possible(your cup suddenly taking energy out of the room and becoming hot again), unless if you have an outside influence.
Now we do have a thing called heat pumps. These are machines that use electricity to move heat from A to B regardless of how hot A or B is. The efficiency does depend on it but it works even if B is hotter than A. This is essentially how a refrigerator works, it moves heat from the cold inside, to the hot outside.
If we to use a heat pump connected to the outside, which is basically a reversed AC , and then use that heat to generate electricity well.. I doubt it would be net positive.
It’s an interesting idea, at least, since you can’t get more energy out of a system than you put in, by draining heat from the atmosphere, you could lower the ambient temperature around the location. The problem with using (thin) air for this project is the incredibly low ROI for such a project. If one assumes a given volume of air, at a specific rate of motion upwards and a particular mass, one quickly finds that the size of a generator needed to produce energy from that volume would be too large (given current materials technology) to produce enough power over its lifetime to overcome the costs of construction (and its not a close margin). It’s not “free” energy, either (as some will try to claim), because the air is being heated by the sun and other human processes. It’s just the absolute least efficient way of using solar energy to provide power.
So you want electricity. In order to generate electricity you need to do work. (spin magnet) If you want to turn heat into work you need heat to flow.
In a simple model you have two heat tanks you either heat one up or cool the other, the point is temperature difference. If you have that, heat starts to flow from the hotter to the colder tank. Then with a machine you can extract some of that heat and turn it into work.
So in order to get work out of heat you need some kind of temperature difference. You can also make cooling machines where you imput work to maintain a cycle and the cycle pumps heat from the colder tank to the hotter like a fridge. A car engine makes fuel ignite and its rapid expansion does work which we transfer to the road through the tyres.
So you need to maintain a temperature difference which either requires you to heat something up or cool something down. Both of them require energy and you can get some of that energy back in the form of work. Heating water to produce steam for instance is pretty efficient cooling something is less efficient.
By the way what warms the air is the Sun (indirectly) so extracting the Sun’s energy directly makes more sense and we are already doing that.
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