Before you jump all over me for asserting the idea of perpetual energy, this is a 4.5 billion year energy machine that I think might also be perpetual. As long as the earth and sun remain intact, this idea will work for sure. So... if we have all arguments out of the way, here is the idea a 10 year old can understand (note it could be a smaller scale, but let's go big):
I want to pull ocean water up the hill over the continental divide between LA/San Diego and Phoenix. Once it crests the hill, gravity provides more than sufficient energy to power cities, desalinate water, and turn desert into farm land. So... how to get that ocean water over the hill?
First, the wind farm at the top of the hill on I-10 is sufficient. 4.5 billion year energy machine is proven.
BUT. I have a more interesting idea:
I will bet you that the laws of thermodynamics can push water up a hill. If we were to paint the pipe different colors (start with black/white), the pipe and water contained within would expand and contract from the heat of the sun. This creates energy that would push on the body of fluid and with some good engineering, different shaped pipes, intelligently painted sections, and some reservoirs to provide a holding tank, we could push water up the hill just using the heat from the sun expanding water. Wouldn't be simple, but wouldn't be all that difficult either.
Solar power using paint and pipe only. I am 100% certain it would work. Once the water is at the top of the hill and over the continental divide? Effectively perpetual energy. Free water. Free energy. For 4.5 billion years.