Watt*day is weird, but at least unit of energy. Watts a day is not. Really common mistake in general to use kWh as a kW. Watthour is unit of energy. As watt is

Watt*day is weird, but at least unit of energy. Watts a day is not. Really common mistake in general to use kWh as a kW. Watthour is unit of energy. As watt is energy by time period. So you get back to units of energy. Technically watt/day could be change in power consumption.