See renewables as fossil fuel saving addition to the grid. Yes, you need conventional power generation to cover the worst case scenario. Yes, it will make the power grid more expensive. No, it will not make it less stable if configured properly. Every Joule generated by a renewable source saves a Joule from fossil fuels for future use. Every Joule saved on fossil fuels means less import (for most countries). So, financially for most countries, renewables are like a savings account which pays back over the next twenty years.
I disagree with the statement that highly variable sources of generation won't make the grid less stable. The more non-dispatchable variable generation there is the more quickly dispatchable firm generation you need to make up for the power which can suddenly disappear. Electricity systems use the frequency in the short time frame to determine if more or less power is required, big changes in generation cause changes in the frequency, which is one aspect of grid stability.
The current price of fossil fuels is not sustainable, and has wildly fluctuated over the last decade. It's not really a metric that can be used for long term planning, except to say that fossil fuels are finite (in the "human scale" of time. Everything is finite if you want to get pedantic.), and therefore the cost will eventually go up if we keep relying on them.
The varying monetary cost of fossil fuels also causes huge destabilization of the world economy (See 1973 OPEC crisis etc). It would make the global economy much more stable if we could eliminate such an unpredictable variable.
Also, mathematically, something that is "renewable" will, given time, obviously provide a better ROI than something that isn't. The figure of 20 years may not be accurate, but fossil fuels will never pay back. Once used, they're practically gone for good.
>Also, mathematically, something that is "renewable" will, given time, obviously provide a better ROI than something that isn't.
Only on a global scale, but people don't act globally. The ROI for the actual entity buying the windmills will be worse if natural gas prices are almost nothing.
