# How do solar panels and wind turbines prove the law of conservation of energy?

The law of conservation of energy makes sense to me in certain systems but in others I can't seem to comprehend it. For example, a car moves because the stored chemical energy within its fuel is converted to heat and mechanical energy which in turn makes it gain kinetic energy. In this scenario the law makes complete sense because the potential energy within the fuel is being used to make the car work. Therefore the energy that was stored is equal to the one that's lost in heat and sound + the one thats making the gears move and making the car gain kinetic energy. But in context of solar panels, they're generating electricity by gaining heat energy. But aren't they technically just creating energy instead of gaining it from the sun? Because on a larger scale, how fuel gets burnt and loses it's energy to the motion shouldn't sun too lose it's energy to maintain equilibrium? Same with wind?

The sun is turning hydrogen into helium, which produces energy from mass. This energy is ultimately radiated as an enormous amount of light: about $1370\mathrm{W}/\mathrm{m}^2$ reaches the top of the Earth's atmosphere.

Solar panels take some of this light energy and make electricity from it (note they aren't using what we would think of as heat: they need shorter-wavelength light).

Wind turbines work indirectly: some of the incoming energy from the sun ends up heating the atmosphere: differential heating causes movement of air, which is wind. This movement has kinetic energy, and wind turbines extract energy from this. The processes involved in turning sunlight into wind, while straightforward in principle, are actually extremely complex in detail.

So both of these systems rely on energy coming from the Sun. Of course, so does a car: in the case of a car, light energy from the sun gets captured by photosynthesis and turned, ultimately, into oil. That captured energy is then used, eventually, to run the car.

So the only place, in this entire system, where energy is 'not conserved' is in the Sun. And that's because, of course, energy and mass are really the same thing, and this is what is conserved. So the Sun is (very slowly) turning some of its mass into energy.

Finally note that the law of conservation of energy can't be proved: physical laws can only be disproved: this is an important point to understand. What you should ask, rather, is how do wind turbines & solar panels agree with energy conservation, or how do they fail to disprove it, not how do they prove it.

• Thanks a lot :) It's kind of clear to me now! Have a good day and thanks again – user136975 Nov 27 '16 at 17:42

I am not sure that I understand exactly your question, but if your query is where all this energy that is transformed into electricity comes from, the answer is EM radiation of sunlight. I guess that in the absence of Solar Panels and Wind Turbines, the earth would be a little bit hotter and less windy place.