The numbers I have seen usually comes from something like this

https://docsend.com/view/adwmdeeyfvqwecj2

However, it's a terribly bad faith argument.

Essentially, they wrap up everything that isn't involved with ledger maintenance (ATM power, data center power for running the website, Air conditioning at branches power usage) and compare that to Bitcoin, which is only doing ledger maintenance. They do that, because if you had a true apples to apples comparison, you'd end up with kwh of power usage. That's because a ledger is computationally cheap to maintain over a trust network. We were able to do that in the 70s with servers that had no more power than today's raspberry pis.

And how do we know it's garbage? Because if banks stopped doing their own ledgers and instead did everything through bitcoin, would their power usage drop? Absolutely not. They'd still have branches, ATMs, and data centers running their websites. In fact, some banks do manage BTC. Do those banks have lower power footprints compared to like banks without BTC? Absolutely not.