Currently SolarIn expects Wh values for PowerDatum entities to be provided as a daily-resetting offset value. This came from the face that early inverters supported by SolarNode reported their data that way. Other inverters, like SMA, report an absolute Wh value, and SolarNode currently has code to calculate that as a daily offset value. That calculation can result in errors, because of the way the "last known" value which is used to calculate the offset is stored in the node's database, which might be lost on a power outage.