[dTal]

From a certain level of abstraction, if countries always did the economically rational thing, we wouldn't be in this mess at all. Building out solar capacity requires planning and foresightedness and political will. Hell, America could transition entirely to solar power for a fraction of the price of the Iraq war - in that sense, sustainable power is already cheaper than carbon-based, once you factor in the externalities of middle-eastern instability. If you factor in all the externalities - pollution, environmental destruction etc - then sustainable has been "cheaper" for a very long time.

The trouble is that countries are not purely rational, and do not factor in all externalities.