Environmental Capital - WSJ.com : Renewable Energy: California Says It Won't Be Cheap or Easy

The California Public Utility Commission set out to determine just what that means: “It is now clear that 33% renewable energy is an important part of California’s clean energy future. As a result, the state must start asking the question how will the state achieve 33% renewable energy by 2020?”
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The intermittency problem is dicier. Wind power is an exponential game. Just as bigger turbines and higher wind speeds exponentially increase the amount of electricity generated at wind farms, adding more intermittent wind power to the electricity grid exponentially increases the costs of meshing that clean energy with the rest of the system, California’s electricity system operator found. Or as CPUC puts it, “As the state increases its dependence on intermittent renewable resources, the system must still provide reliable electricity services, which will add to the total costs of reaching a 33% [renewable standard].”

That last quote in bold is priceless.