solar power
people seem to think the amount of energy from the sun is infinite. and yeah. it's a lot. some 10^17 watts. which is some 10,000 times more than people use. okay let's build some solar farms. the first thing that's surprising is that the efficiency per square meter of land surface is about 2%. that's because the conversion process itself is some 15% in the best case. which is actually quite rare. ie only when the sun is directly overhead with no clouds. anywho. we're down to some 10^15 watts. solar farms need to be built on flat land. most of which is already in use for other essential things. like food production. and cities. deserts are good. maybe some 1% of the earth's surface area would be available. which means the amount of solar power we can harvest is about the same as the total amount of energy we currently consume. hardly infinite.