YES, now it works !
at least it no longer crashes, but you'll have quite some work to do to make it really nice and useful ... as you wrote yourself "This is the very first release! There will be problems and the mod is far from complete."
most of all, the GUI only shows the names and a green bar, but no details on what the bar represents (J, kJ, MJ, ...). without any numbers, i can only see how much filled some setup is, but if i have several groups i can't compare them to each other. and most of all, the GUI takes away lots of space, always increasing in size when new groups are added but never decreasing when items and groups are deleted. at least bars are reused when i use the same name a second time, and also the GUI is removed when i have removed the mod (until the mod provides more functionality)
from the description on the info "monitor energy production/storage in your solar panels and accumulators." i had hoped to see more details like number of panels and accus, a computation of the current ratio and advise on how many to add for optimal ratio, etc. but currently it provides barely the same info (if at all) that i already can see on the third line "Accumulator charge" on the vanilla power tab by clicking any powerpole in my network. your mod will be really useful if i have several power subnetworks which can be shown at the same time and/or if i get help on ratios or similar.
fun fact: sometimes mods create new items based on items from other mods. and sometimes mods create new items based on new items based on items from other mods, etc :-) when i removed this mod, i had expected to see in the migration list that the recipe for pmon-power-monitor was removed, but i found a second recipe that was removed: item-logicarts-item-pmon-power-monitor-incineration LOL, what a beast of a name :-) and probably a nightmare to debug if yet some other mod messes up any parameter like icon size of such an indirect item
