One of the policy goals motivating programs to increase renewable energy investment is that renewable electric generation will help reduce emissions of CO2 as well as emissions of conventional pollutants (e.g., SO2 and NOx).
As a policy instrument, Renewable Portfolio Standards (RPS) encourage investments in wind, solar and other generation sources to reduce pollutants emissions from electricity production. A larger penetration of renewable energy sources will lead to larger emissions reductions. We have found that the effects of transmission congestion in large-scale power systems may increase the emissions of CO2 and conventional pollutants associated with investments in large-scale renewable power generation. The emissions impacts of renewable energy sources depend on location as well as the size and quality of the renewable resource. We analyze the emissions impacts of large-scale wind power in the Western United States using a utility-scale generation dispatch model that incorporates the impacts of transmission constraints, and find that locating large-scale wind farms in some areas leads to an increase in overall emissions of CO2, SO2 and NOx. The location of wind farms influences the environmental impact via changing the utilization of transmission assets, which affects the overall utilization of power generation sources. Our results suggest that RPS alone may not have the intended environmental benefits, and a refined systems-level approach to renewable policy development is necessary.