City of Denton, TX has a goal of using 70% of electricity from wind and solar by 2019. In order to achieve this goal it is buying 12 highly flexible Wartsila internal combustion-based gas generators with a total capacity of 225 MW. These generators have quick start/stop times and high ramp rates, which are required when balancing wind and solar. The claim is this allows wind and solar to act like base-load generators and the fossil-fuel generators to fill in the gap. Interesting narrative.
For more information, see http://www.globalenergyworld.com/news/26696/Wartsila_supplies_225_MW_Pow...
However, i suspect, this configuration may not work for island grids, because of low overall grid inertia. Denton must be getting its primary frequency control from ERCOT, but an isolated grid would need inertia--possibly from wind generators with synthetic inertia.