[Izkata]

The live action films I don't think so, but a few of the shorts in the Animatrix were supposed to be an accurate history archive from the creation of the first machines all the way through the war and the creation of the Matrix. The shorts both included it and kind-of came up with an explanation:

During and before the war, the machines were mostly solar-powered, so blocking out the sky was a last-ditch effort by humans to stop the machines that almost worked. But the machines developed a new form of fusion that used human bio-electricity as some sort of activation or catalyst. They weren't being used as energy directly.