Using wind farm production data and predicted production from solar thermal power plants, a U.S. Department of Agriculture(USDA) engineer says it's possible to match up power generated from the two sources so they balance each other out, at least in west Texas and the Texas panhandle, and in parts of California.
Agricultural engineer Brian Vick at the USDA Renewable Energy and Manure Management Research Unit in Bushland, Tex. looked at, among other things, wind farm-generated electricity at the three major wind farm areas in California (Altamont Pass, east of San Francisco Bay; Tehachapi Pass in the high desert near Mojave; and San Gorgonio Pass in the low desert near Palm Springs). The hourly wind farm output during the day from these facilities doesn't match the utility electrical load very well. In spring and summer the lowest winds generally happen at mid-day when utility load is highest. But he says installing parabolic trough solar thermal power plants in the Mojave Desert would help balance out the wind farm generation since highest solar generated electricity will be during mid-day.
Similarly, the solar energy from Mojave Desert and wind energy in the major wind farm areas are not a good match to utility load during the winter in California, but if the number of wind farms were increased east of San Diego, then the utility renewable energy match would be improved (because wind energy is highest during the winter in this area). Combining wind farms and solar thermal power plants with storage would let a larger percentage of the electrical load in California be met by wind and solar energy than by either renewable resource separately.
He says the most efficient storage system is one being used in solar thermal power plants, where the sun's heat is used to heat water or other fluids. After the sun sets, the heated fluids produce steam to generate electricity.
The excess electricity generated by wind in the late night and early morning hours could be pumped into the grid and removed by storage facilities (like pumped-storage hydroelectricity or compressed-air energy storage facilities) to match the utility loading in the daytime.
More info from the USDA: http://www.ars.usda.gov/is/pr/2010/100812.htm