This already happens without the use of bitcoin. People with solar panels can generally sell excess production (that generally occurs during peak demand times) back to the "grid" at retail prices. The cost of transmitting this energy is borne by the utility companies (and are ultimately socialized).
Well, the problem with that is that transmission of power over a grid over long distances is typically inefficient. It may be more cost-efficient to simply convert the energy to cryptocoins which are used later to offset the cost of fuel. Also, what if there is a mismatch between renewable power production and demand over a large region (e.g. on a day that is particularly sunny or windy over much of the country). Then, who do you sell the excess power to? It still has to be stored somewhere, or used. Currently, this is not as big of a problem, since renewable production is still only a small fraction of demand in most countries, but we can anticipate that this will not always remain the case.
I do not think using "green" energy is a good way to use miners to make bitcoin
I disagree. The cost of photovoltaic panels has come down dramatically in recent years, to the point where in many places, PV is now cheaper per watt than grid power, with only a low payback period (few years) for capital cost recovery. I know a miner who is building a complete solar-powered mining installation. His operating costs are extremely low, and so his profit margins are much better than other miners'. As other miners realize the feasibility of this approach, and the cost/watt of PV panels continues to come down, I predict that PV-powered mining will become more and more popular, and eventually will drive all traditional grid-powered mining out of the market due to the cost differential, also helping to drive widespread adoption of distributed solar power worldwide (at least in high-insolation areas).
Cheers...