Improved hydrological conditions in California this year resulted in excess power generation over 2015, but the margin of improvement is shrinking now as winter approaches, and December has seen hydro output fall faster than it did last year.
In November, average hydro generation in the CAISO region was up more than 1 GW, or double, the 2015 level. In December however, output has fallen slightly while it improved last year, so the difference has declined by more than 20%, to an 800 MW surplus.
Both wind and solar output have also fallen off faster, resulting in less renewable output overall. Solar is averaging 1.49 GW in December, down about 20% from November, though up 28% on 2015 due to increased capacity.
And Wind has averaged 967 MW in December, though last December averaged 1,295 MW for the full month.