There are basically two numbers here:

1. Net usage after selling off excess energy 2. Net usage assuming there is no demand for excess when you have it (maybe everyone on the grid has solar panels)

Achieving 100% in #1 is great and I applaud Google for it. If everyone did this we could drastically reduce overall usage of fossil fuels, but I believe the fear is that people won't know the distinction and will assume "if everyone does what Google does we will all be 100% renewable" and that isn't true.