Hi Ron

The ‘affordable’ aspect seems to be the main point here and if I understand the pre-fabricated nature of the build, I think your best using a ‘roll out’ photovoltaic solar panels as shown here:

You will have to contact the manufactures for figures and costs, but the important thing is; the technology exists to help your situation.

This is not a solution for a typical slate/tiled roof covering.

Hope this helps.