Where would the energy from renewable sources go if we didn't use it?

Well, just that. Are anyone in particular missing out on this energy? Does it matter?

A windmill or water-powered turbine for example – we take some of the energy of that resource, and it has been weakened as a result. The wind or water downstream is not quite as powerful as it would have been if we didn’t interfere. But the difference is so slight that no one notices.

At least not for quite a while. Then we’re back to square one.

It would end up as heat, or stored as chemical energy in plant material.

As an excellent rule of thumb, whenever the question is “where does the energy go”, the answer is almost always “heat”.

so by not using them, you are contributing to global warming.

And all you’re doing by using the energy is slightly moving the moment at which it gets turned to heat - e.g. for wind power, either the wind turns a turbine which drives a generator which produces electricity which makes a lightbulb glow, which gets hot, or the wind just slams into a mountain or another air mass or something and generates heat by friction.

Right. Either way, that wind energy for instance is headed for heat. The question is what it accomplishes along the way. If it goes into a wind turbine, it does some useful work prior to being dissipated into heat.

Energy, left to its own devices, simply spreads out until every place has a small but relatively equal amount. Humans gather a bunch of energy into one place so we can focus it on doing something we want.

Like putting children in a sweat-shop.

thanks, great answers!

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Sympathy for the Second law