They certainly should work at the power level. My utility is ~36% renewable in their power mix right now, but I pay for 100% and that extra money causes them to go out and buy extra renewables for the remaining 64% of my power. I'm not under any illusion that on a cold, still winter night that my power isn't coming from coal base load - but I have high confidence that they really are buying that extra power, and that in turn creates more demand for solar generation.
My employer does something similar, we buy the RECs from something like a third of the output of a local solar farm (under contract) and then also buy dirty power from the utility. That should ultimately wash out.
Though what I can't figure out is how that solar power is actually accounted for when it hits the grid. It's been severed from the renewable energy credits (that we bought) so presumably it must not count as a non-carbon power source when it enters the grid, but I can't find a category for "non-green solar power" on any of the utility reports. Anyone know where it goes?