Here's the sauce.
https://www.robeco.com/en/insights/2019/04/spending-one-bitcoin-330000-credit-card-transactions.html
This Robeco article from 2019 compares the energy consumption of Bitcoin (at the time) to the energy consumption of Visa. In that article, it says,
"The digital currency consumes 511 kilowatt hours of electricity for one coin to change hands, according to research by digiconomist. That is equivalent to 330,000 Visa transactions, making it the most energy-intensive form of electronic trading known today."
End quote. Reversing the equation, and figuring the answer for one Visa transaction in kWh results in the answer 0.00155 kWh (the article below states 0.003, but let's give Visa the benefit of the doubt and say 0.00155)
That is very efficient, however it is not more efficient than Nano. According to this article, among many others, Nano transactions require only approximately 0.000112 kWh of electricity for a single exchange.
That means, at best, Visa is 13.84 times less efficient. At worst, 26.79 times less.