Home Assistant lets owners add power-only devices, solar production and home meters to Energy by offering to create the missing energy sensor during setup. It can also reuse a sensor that already calculates the total from the same reading. A newly created sensor starts counting then; it does not reconstruct earlier usage.
The same setup works for gas and water sources and individual water devices that report a flow rate. The calculation follows the rate’s time unit, so a litres-per-minute reading produces a volume in litres.
Grid and battery setups need separate power readings for each direction. A single signed reading does not get the offer, because one calculation cannot separate the two directions.