There was once a time when man kind worked on solar energy. Well not to produce electricity, but to grow crops, to light the outdoors, and other various things. We did not have the capacity to do much work at night, due to the lack of light. Sure there were lamps for inside the house, but this was about it, work did not continue into the night. Transportation was slow, so most food was local, people had to manually do the farming with the assistance of horses, and all this worked to limit the population of the world.
Then came oil and coal. They increased the hours that could be worked, the distances that could be traveled, the amounts of food that could be grown, the size of cities that could be built etc etc etc.
Not only did oil and coal cause the population explosion. But it caused most of our climate woes as well.