I have read a lot of articles about exascale and found out that it may consumes approximately 20MW power envelope. Is it a daily basis or a yearly basis or every second?
Please enlighten me. Here are the papers I have used.
One of the main challenges in achieving this goal is power consumption, which a range of HPC system operators have suggested be limited to 20 MW for a full exascale-capable system to mitigate cost of ownership and new power delivery infrastructure costs 
An exascale supercomputer is envisioned to comprise of on the order of 100,000 interconnected servers or nodes in a target power envelope of ∼20MW, with sufﬁcient memory bandwidth to feed the massive compute throughput, sufﬁcient memory capacity to execute meaningful problem sizes, and with user intervention due to hardware or system faults limited to the order of a week or more on average .