I think in many places, gas peakers are already available. In the long run, we're probably going to need to do something else, but who knows where storage tech is in twenty years?

In Denmark, home of the biggest wind power companies, this is a frequent topic of discussion among people interested in energy, but the answer is really that there are many options on the table, including expanding the grid. While many options are too expensive to see much use today, that will probably change over years.

New ideas are also coming up, e.g. this

http://www.salon.com/2017/08/09/alphabet-turns-to-molten-sal...

which might work except they should just store the heat in rocks instead of molten salt which is a PITA to work with. I know of at least two independent designs (both Danish) that store the heat in a huge repository of insulated rock/dirt and use a turbine to get electricity back out, at an efficiency about 40-45% IIRC. A prototype plant recently received funding. Not sure it has reached the international press yet. I don't think it has much future in Denmark, though, there's plenty of hydro in Scandinavia.