As wind farms occupy our wild hilltops, I look out the window and see dozens of new structures that are potential sources of renewable energy.
Governments in wealthy nations should mandate photovoltaic roofing systems for all new commercial and residential buildings (private houses under a certain modest size or cost would be exempt), to come into effect in, say, five years.
I'm not taking about solar panels, but integrated systems to replace tiles or shingles, connected to the electricity grid for two-way transfer of power.
Cheap? No. But if the requirement is there, technology will rise to the occasion. Efficiency will go up, cost down. There will be a payoff for the poorer nations too, which tend to be located in sunnier climes.
Since the size of a roof generally corresponds to the size of a building, the cost of photovoltaic roofing would be an indirect tax on energy consumption.