There are many ways to transitionally contribute to green energy but why should you build it with a smart contract? Like what are the actual benefits or the urgency of tokenizing green energy/solar stations? Personally, nowadays it seems like smart contracts are just some another buzzword like the word blockchain whose idealized to solve many real words problems magically.
If you try to raise funds via traditional methods, it is much more difficult as if you want to release your bonds, it will require a lot of documents and different difficult procedures. Nevertheless, if you do it via smart-contract, you can perform it just releasing a new ERC-20 token on Ethereum, what is easy and don't require any documents. The main thing is to organise marketing campaign and ICO so that there will be investors.