This AOPA article https://www.aopa.org/news-and-media/...rical-aircraft links to this clarification from the FAA Office of the Chief Counsel https://www.faa.gov/about/office_org...rpretation.pdf which notes that based on the NPRM and Final Rule, there was no intention for the omission of "engine-driven" to be significant. So we should treat the regulation as if it says "engine-driven electrical system". Wonder why they didn't just write the FAR that way then?
Also-- "The legal interpretation states that the FAA may make a technical amendment in the future to eliminate the discrepancy between 14CFR 91.215 and 91.225".
That would be nice. It would also be nice if they would make a technical amendment to address this problem I've pointed out in trying to figure out exactly where FAR 91.225(e)(2) is supposed to apply. It's becoming pretty clear to me that it's only supposed to apply within the lateral boundaries of Class B or C, just as is explicitly stated with FAR 91.255(d)(3).
Btw that's a little disturbing that your local FSDO wouldn't have been able to clarify that for you, re what is an electrical system. It's becoming more and more clear to me that the local FSDO is not the place to go for answers to questions unless the situation is very cut-and-dried, and maybe not even then.