Seems like this paper answers some of those questions: http://www.energy.siemens.com/us/pool/hq/power-generation/power-plants/gas-fired-power-plants/combined-c

Seems like this paper answers some of those questions: http://www.energy.siemens.com/us/pool/hq/power-generation/power-plants/gas-fired-power-plants/combined-cycle-powerplants/Fast_cycling_and_rapid_start-up_US.pdf http://www.energy.siemens.com/us/pool/hq/power-generation/po... tldr: natural-gas combined-cycle power stations can achieve ~30 min startup times, and are being used to provide flexibility in the grid.