A report from Bentek recently caught my eye because it provides yet another reason we should be getting away from coal-fired power as fast as possible. It turns out that adding more wind to Colorado's energy supply has actually increased the level of local air pollutants because coal plants don't play well with renewables.
The report, "How Less Became More: Wind, Power and Unintended Consequences in the Colorado Energy Market", explains why. Because wind power is a 'must take' resource, other power plants have to ramp up and down as the amount of available wind varies. It turns out coal-fired plants don't behave well when 'cycled' like this to accomodate wind--they actually spew significantly more environmentally damaging emissions into the air.
The odd result is that as the amount of wind power added to the grid increases, the air quality actually has actually gone down. The report concludes that unless the additional wind capacity is coupled with significantly more gas capacity, a reduction in coal capacity, or a combination of the two, the higher RPS will drive SO2 and NOX and possibly CO2 emissions higher.
LINK: A nice summary of the report is also available on IWAG's site.