[orev]

How would you move the solar energy into the piles of dirt? You’d need something like an array of mirrors focusing the rays, which has definitely been done already but has drawbacks. Electricity can easily be moved to where it’s needed.

[quickthrowman]

You could heat up a metal heat exchanger that you circulate a working fluid through. Probably easier to just convert sunlight to electricity to heat via resistive heating, less maintenance.