Exactly . . . If it's voluntary, what happens if Google and all the other ratepayers participating in this special tariff drop out five years down the road into a power plant that should have at least a 25 year life? To build a renewable plant in a carbon-tax free world, you need credit, contracts, or government mandated compliance markets that provide some sort of premium. The utility is not going to be left holding the bag, they'll get to recover their investment through the ratepayers still standing.