While I didn't take individual screenshots, I did find eighteen blocks and marked the locations on my map when I found them. One of them is a presumed location marked by a (?) because my count of marked spots on my map came up one short of what was in my inventory and that was the only other likely location (with a deactivated ruin guard). Easiest tell for finding them is there is almost always, if not certainly, metal scraps in the area. Some of these locations are tied in with the Aranara questline and may be inaccessible until you've made it to the right spot in the questline.
UPDATE:
Cross-referenced this amazingly in depth post by YURAI https://www.hoyolab.com/article/7285498 as I found an odd incongruence in our counts. With theirs seemingly missing the four in the lower left the count came up to nineteen and I found that they'd noticed one I hadn't - sitting in a pipe at Devantaka Mountain. With that pipe taken into consideration the total then comes to 19 energy blocks.
(Additional spot marked in purple below)
Absolutely check out YURAI's guide because the depth they handled finding these with is amazing and should be even more helpful with finding the initial fifteen!
UPDATE TWO:
Another cross reference has revealed another. My initial, singular speculative location (the ruin guard location I marked with a '?') was proven correct, but not in the way I expected. While going through and trying to give the damaged guards cores I found that the guard I initially marked as being an energy block location still had an energy block next to it. So where did my extra block come from? Cross referencing this article https://game8.co/games/Genshin-Impact/archives/387045 I realized my mistake - I marked a correct location but it wasn't the same guard I initially got the energy block from. The guard I initially got my energy block from was at this location here:
and this guard brings the total of energy blocks to 20.
As both reference articles linked state: There is an achievement tied to giving the guards the cores, I only found that last one because of working on this achievement. While my presentation here is incredibly chaotic I do hope that this is useful to others and I welcome others referencing the locations I've marked and putting together a more coherent guide.
