Another way to throw a different & larger lasso around the entire problem of energy monitoring is to go with a whole-house approach based on a multi-circuit-capable special-purpose hardware such as the Brultech GEM. I bought one of these units a few months ago & can now see per-circuit usage for the entire house. At around $500-$600 or so, not cheap, but perhaps a fair cost when compared to the time & coding investment required to try to piece together comprehehsive usage based on measurements of individual devices.
Hardware-level physical current monitoring also accounts for normal line-voltage variations in real time. (As much as +/- 7% from nominal 120V AC on heavily-loaded circuits.) A well-designed hardware solution also automatically measures & accounts for AC power factor, a very significant issue when dealing w/ inductive loads & switching power supplies.
IMO the GEM is a good piece of hardware, built-in web GUI is rudimentary but functional. Documentation is adequate but not super well-organized.
At some point I will work on getting the GEM hardware integrated w/ OpenHAB.