The newest designs (#39, #38) are very strong. I like the green/grey semicircular symbol in #39- it's a great blend of various renewable energy symbols. I wonder if you could use some of the gold color from #18 in there.
In #38 I would like to see "TOPO" stand out more- perhaps make it bigger, or darker, or heavier, etc.
In both of those I would like to see sans serif typeface, which I prefer in general.
Thank you for the feedback, apreciated. Here comes the revisions based on your request. Please do not hesitate to leave comment on any of them if you think of a need for improvement. Thank you.
The full circle symbol in #52 and #69 points to solar and wind, two other renewable energies that we don't want to copy. I don't think those work. But before I completely write it off, can you try #53 without the yellow?