http://digiconomist.net/bitcoin-energy-consumption

Description	Value
Bitcoin's current estimated annual electricity consumption* (TWh)	14.02
Annualized global mining revenues	$1,901,053,761
Annualized estimated global mining costs	$700,823,391
Country closest to Bitcoin in terms of electricity consumption	Slovenia
Estimated electricity used over the previous day (KWh)	38,401,282
Implied Watts per GH/s	0.301
Break-even Watts per GH/s (based on 5 cents per KWh)	0.815
Electricity consumed per transaction (KWh)	147.00
Number of U.S. households that could be powered by Bitcoin	1,297,821
Number of U.S. households powered for 1 day by the electricity consumed for a single transaction	4.96
Bitcoin's electricity consumption as a percentage of the world's electricity consumption	0.07%

Quote
To put the energy consumed by the Bitcoin network into perspective we can compare it to another payment system like VISA for example. Even though the available information on VISA's energy consumption is limited, we can establish that the data centers that process VISA's transactions consume electricity equal to that of 50,000 U.S. households. We also know VISA processed 82.3 billion transactions in 2016. With the help of these numbers, it is possible to compare both networks and show that Bitcoin is extremely more energy intensive per transaction than VISA.

This does raise issues with what is termed gad price. Explains why some transactions take longer, eg more lucrative for miners to go after higher fees, leaving the smaller transactions to later.

Fascinating. Thanks

I had my rigs running for only eight months before they couldn't turn a profit due to the power they were consuming. It was a fun project though.