A baseline value for network power consumption can be found by multiplying the total network hashrate with a "best case" value for the power/hashrate ratio that a miner can achieve.
As a side note, people often confuse power (W) and energy (power x time, eg. Wh). For instance, assuming an average daily P<sub>Nd</sub> of 821 MW we can calculate that days Energy consumption by multiplying by the number of hours in a day.