Canadian Politics Today

What you seem to be referring to as "idle capacity" is actually existing capacity.

Large amounts of renewables require new dispatchable capacity to provide backup. Existing baseload sources cannot provide that. Dispatchable capacity is much more expensive than baseload but the exact cost of this dispatchable capacity depends on how often they can sell power. As the fraction of renewables increases the economics of the dispatchable capacity decreases to the point where plants close without subsidies. This is what has already happened in Germany.

IOW, the dispatchable capacity needed to balance reneweables is an extra cost and the reason why wind and solar always cause electricity rates to go up despite the illusion the sun and wind are "free" resources.