Recent developments in wind technology coupled with desparately needed utility grid upgrades make wind viable for a vastly larger proportion of our electric power than is widely recognized. Opponents will tell you that the intermittent performance of renewables is a show stopper. They will tell you that cloudy and calm days render renewables inherantly unreliable. However this flat earth view only makes sense when applied to individual or small clusters of renewable resources. When the grid is utilized to aggregate renewable resources the picture becomes entirely different. Lets take a look at wind only, and save solar for another day.
In a study published in 2007 researchers looked at wind farms in the southwest and compared the reliability of their output to that of coal power plants. Wind Aggregation southwest baseload . It was found that as the number of interconnected wind farms increased, the percentage of rated power that could be counted on with the same certainty as that coming from a coal fired plant was 15%.
The study was done in a geographically contiguous region. While the region was large it was still within a meteorologically similar area. The key to increasing the baseload equivalency of wind (without storage) is to interconnect areas that are meteorologically decorrelated. Three such high wind areas are the atlantic seaboard, the northern great plains and the region described in the study above. If the transmission capacity between these three areas were enhanced the baseload equivalency of windpower would be dramatically increased. – If someone knows of a study quantifying this, please post a comment with a link to it.
Improvements in turbine efficiency can also expand the effective baseload of wind. In particular lowering the the wind speeds in which they are able to extract energy from the wind can have a substantial impact. There are two reasons for this. The first is that it allows the turbines to be economically deployed in a larger geographic area and second it increases the capacity factor of the turbines.
This link shows how windspeeds vary throughout the continental United States https://handlemanpost.wordpress.com/2011/10/04/wind-map-of-us-great-plains-is-just-loaded-with-windpower/ . By lowering the windspeed at which a turbine economically extracts power from the wind, the siting opportunities are dramatically expanded. By placing the turbines in geographically dispersed areas they become further decorrelated in terms of when they are operational. This yeilds a statistically smoother aggregate output, translating to higher effective baseload.
By expanding the range of windspeeds for which the turbines are operational the capacity factors increase. Since the Stanford study listed above was written, substantial strides have been made in increasing turbine efficiency, capacity factor and in reducing the wind speed at which turbines generate power. More on this here – https://handlemanpost.wordpress.com/2013/03/09/wind-turbine-increases-efficiency-by-25/ . Additional advances promise to continue the trend of tubine improvments, this GE research project offers a glimpse into the possible future of wind – http://www.nrel.gov/wind/news/2013/2066.html