Why not mandate that new homes need to have equivalent solar built somewhere. So I build a home with a 700sqft roof, an additional tax is added that goes towar

Why not mandate that new homes need to have equivalent solar built somewhere. So I build a home with a 700sqft roof, an additional tax is added that goes towards building 700sqft of solar at a solar farm. In fact it would be cheaper since installation would be much cheaper on a large scale and solar farm can buy panels in bulk.