In many alt energy scenarios, we're replacing most operating costs (such as fuel) with higher capital costs, then relying on subsidies and accellerated depreciation to make it profitable.

There is always what I call the Tesla problem. When solar / wind / geothermal hit a certain percentage of the market or when fossil fuel burning competitors switch, the subsidies start going away. If they hadn't figured out how to make it without subsidies, they're in trouble.

Likewise, for anything capital-intensive, interest rates can have a huge impact. If rates were close to zero for years and then rapidly rise, some investments don't look as good at their former prices, so prices must fall in order for rate of return to become competitive again.