I like that these are very sharp looking, and I like the idea of a green letter that pops out. I also like the interesting elements going on with the letters, such as the "o"cutting into the "p" in #15 and #16, and the white bar connecting the "po" in #14.
Here are some issues I see: - in #16 and #15 the letter "p" is hard to read. - in #15 and #14 the colored letter "o" looks like a power button, thereby confusing the nature of the "energy" we are dealing with. It says electricity more than biodiesel.
I appreciate your effort, and hope you keep playing with the design.