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Estimates of Bitcoin's Soaring Energy Use Are Likely Overstating the Electric Power Required To Mine the Cryptocurrency (cnbc.com)
From a report: The computer process that generates each coin is said to be on pace to require more electricity than the United States consumes in a year. This bitcoin "mining" allegedly consumes more power than most countries use each year, and its electricity usage is roughly equivalent to Bulgaria's consumption. But here's another thing you might want to know: All of that analysis is based on a single estimate of bitcoin's power consumption that is highly questionable, according to some long-time energy and IT researchers. Despite their skepticism, this power-consumption estimate from the website Digiconomist has quickly been accepted as gospel by many journalists, research analysts and even billionaire investors. That model is also the basis for forecasts of bitcoin's future energy use that remind some experts of wild projections about internet data traffic in the mid-1990s that contributed back then to companies spending far too much for capacity they would eventually not need. "Doing these wild extrapolations can have real-world consequences," said Jonathan Koomey, a Stanford University lecturer who pioneered studies of electricity usage from IT equipment and helped debunk faulty forecasts in the 1990s. "I would not bet anything on the bitcoin thing driving total electricity demand. It is a tiny, tiny part of all data center electricity use."
This question seems interesting so I thought I'd do a back-of-the-envelope number myself.
blockchain.info estimates the total hashing power of the bitcoin network at 14,000,000 TH/s. An antminer s9 can do 14 TH/s. Therefore the bitcoin network computing power could be approximated by 1 million antminer s9s. An antminer s9 draws 1372 watts. So if all bitcoin hashing was done by antminer s9s, we'd need 1,372,000,000 watts, or 1.4 gigawatts.
Not everyone is using the s9; some people are still using the s7, some are using ones by other manufacturers. The s9 is very popular however. Let's assume the average efficiency in hash power per watt is 30% that of the antminer s9. That gets us up to 4.6 gigawatts.
I feel good about not using a number smaller than 30% because there is a strong disincentive not to use inefficient hardware. The while I'm sure there is old hardware still hashing, the capacity of the network skews new. Looking at blockchain.info again, we see that half the capacity of the network came online within the last 5 months, so that'll certainly be newer hardware.
The estimate that TFA says is to high is 36 gigawatts, almost 8 times higher than my estimate. So I'll tentatively endorse TFA's view, dependent on the accuracy of blockchain.info's numbers.
Make a crypto-currency with a useful POW then; needs a task with a randomizable search space, and quick verification once a correct/satisfactory solution is found.