Require that public and new buildings make some energy

Why can't government bite the bullet and require that all public buildings make energy using renewable sources for example solar water heating and in particulare solar electricity? British schools would generate huge amounts of energy in the six weeks that they're empty. How much would that eventually save? New houses should also be included. Imagine the sell back savings and perhaps even for the reduction in windfarms.

Why is this idea important?

Why can't government bite the bullet and require that all public buildings make energy using renewable sources for example solar water heating and in particulare solar electricity? British schools would generate huge amounts of energy in the six weeks that they're empty. How much would that eventually save? New houses should also be included. Imagine the sell back savings and perhaps even for the reduction in windfarms.