Gas fired plants have a very quick start up. Wind farms are very unreliable because wind is very unreliable. Solar is only available during the day. As you correctly pointed out there is no way to store extra capacity. Wind farms are given priority not because of lower costs, they really are not when you have to factor in the cost per kilowatt generated as each wind turbine is not cheap, needs periodic maintenance, and suffers many breakdowns. Larger conventional plants and nuclear plants are very efficient and have superior performance between breakdowns. Normally gas fired plants are used to provide extra capacity when needed. They start up quick and are always available when needed. The cost per kilowatt is higher but that is a trade off for reliability.