Rather than giving ROI numbers it would be better to share different scenarios. Ethereum can be problematic with the incoming supply of drivers. I beleive you should inform us more about renewable energy and legal status. I do not believe that it can be profitable with this preferences.
ROI of course depends on several different inputs/assumptions. For scenario part you can find our excel (on google sheets) model and try yourself changing input values to find what the result may be:
https://docs.google.com/spreadsheets/d/116FvwAmpSGVHc9PbMTzmmX_YD5qzkCwDzqjIInNI03Y/edit#gid=8342125We have 1 million token budget for bounty campaign for project supporters, feel free to contact me on facebook: Vakhtang Gogokhia