Solar Farm energy may cost less to produce, but the corporation that owns the solar farm will set consumer prices. So we don't know what it will cost US, except that it will cost the maximum that the solar farm owner can get away with.

Rooftop solar will have a marginal cost of zero because, once the capital costs are covered, the Sun charges nothing for energy.

I'm fine with solar farms, but I don't trust their alleged price advantage under our current economic system.