First, because it's discontinuous (the sun doesn't always present), solar energy can't produce the constant power that we're utilized to.
(Genesa 8:22) Leswi hi swi tivaka leswaku dyambu ra tlhava siku ni siku, hi nga tiyiseka leswaku misava a yi nge tshiki ku hi nyika leswi hi swi lavaka leswaku vutomi byi ya emahlweni.