Energy in transients vs. steady state
Transients, by definition, are very short period.  And (in the context of the vague scenario you describe) they're the effect of either infrequent load switching, or highly periodic 'switch-mode' noise that may result from use of a DC-to-AC inverter, for example, or an actual load drawing non-DC or non-sinusoidal current.  The former can probably be ignored without a second thought, due to the comparative rarity of them. 

As for highly periodic 'switching noise', well, "it depends" on the specifics of the equipment (inverter?) &amp; load in use.  If it were me, I'd want to see at least a voltage waveform, &amp; ideally a current waveform, with the system under various loads, to "see if you have a problem" that needs to be accounted for in your measurements, or not.  But my gut feeling is that the energy in any such 'noise' is probably going to at least 2, probably more like 3- orders of magnitude less (one hundredth or one thousandth) energy than the actual steady-state (DC or sinusoidal) load - if that guess is actually the case, then you can make a call as to whether that matters to your desired measurement accuracy.  In a "regular household", I'd expect not :)