Over the long haul, yes, but in real-time - no. And electricity prices to fluctuate a lot over days, weeks etc..
But indicating that 'price stability' is a point for green is not really fair, when it's almost always going to be considerably more expensive.
Knowing that something is going to be 'consistent, and consistently more expensive', I don't think is a good argument for green.
There are other, better arguments.
You'd deal with this the same way you deal with it in every other commodity market, futures contracts.
Google is in effect doing the same thing as 'buying a future' and it's unreasonable for him to make the argument that this is 'inherently a better thing about green'.
I could buy a futures contract for Oil today and would it be fair for me to say 'Oil is has more stability in prices'?
But Oil shouldn't fluctuate too-too far between $50 and $120 a barrel. And that's just the raw costs. With all other components, which costs will be more fixed, the actual end price of fuel should not change more than 40% in either direction, max.
I'd argue that the greatly varying costs of wind installations, aggregate availability, huge one: supply and demand for electricity overall, specifically for renewable electricity - regulator changes, improvements in technology - definitely create a situation wherein the 'end cost' of renewable electricity is somewhere in the range of the variability for fuel produced by other means.