It is based on an hourly model of the electricity demand for a complete year, looking at carbon reductions of 0, 50, 75 and 100% with various combinations of wind capacity and storage capacity.
The long-term, large capacity storage was assumed to be as Renewable Power Methane, produced by the 'Power-to-Gas' process being demonstrated by Audi at their 6.3 MW plant in Werlte, Germany.