Reduced import dependence
Renewable energy sources reduce fuel import dependence. Wind or Sun do not have to be imported unlike coal, gas or oil.
Also, they contribute to diversification of energy sources.
For example, imagine a system which consists solely of gas power plants. What would happen if gas supplies were disrupted or prices suddenly increased? Therefore, systems must consist of different types of power plants that use different types of fuel, which means that a system consisting solely of wind power plants would be neither viable nor stable.
Energy import/export 2008
(SOURCE: MINGORP, Energy in Croatia)