Average, overall, and other measures are unimportant when talking about electrical power. You need to look at worst case scenarios to understand how much capac

Average, overall, and other measures are unimportant when talking about electrical power. You need to look at worst case scenarios to understand how much capacity is actually required. So, over the course of a year, on what day did renewables supply the least amount? That would provide an initial indication, but would hardly suffice for long term planning. For example, if utility A supplies only 20% of required power from renewable sources on a given day over the last year, you can really only say renewables can be expected to supply 20% on any given day. But you'd need to do modelling or track over a larger number of years to get to the (likely lower) actual number.