Synapse Energy Economics published a study this May that a build out of wind in the midwest power market would lower wholesale power prices by 25%. Savings to retail customers would range from $65 to $200 per year. http://www.renewablesbiz.com/article/12/05/study-midwest-wind-and-transmission-build-out-lowers-power-prices-and-minimally-impacts-rates.
The study is entitled, "The Potential Rate Effects of Wind Energy and Transmission in the Midwest ISO." The market area includes North Dakota, South Dakota, Nebraska, Minnesota, Iowa, Wisconsin, Illinois, Indiana, Michigan and parts of Montana, Missouri, Kentucky and Ohio. Currently about 10,000 megawatts of wind operates in these states.
The paper looks at scenarios of adding up to 50,000 more megawtts of wind energy and the impacts of adding such supply to wholesale market prices. As Bob Fagan, a co-author of the paper states, "The general effect is lowering the clearing price of the market."
The study also includes costs of expanding transmission and finds the consumer savings from lower generation prices exceed increases in transmission costs.
Wind generation, as well as nuclear plants, solar, and hydro units, bid zero into markets and accept the market cleaing price. Wind can do so, because its production costs are very low, typically around 0.5 cents per kilowatt-hour. When wind and other zero bids are enough to meet demand the market clears at zero or can even go negative (see the posting about the strange, real world of negative electricity prices).