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Lets be generous and say bitcoin only uses $50 per transaction.
How much do you think it costs the bank when I buy a coffee with my debit card.
If the stats that mining uses 9% of electric in India are even closely true that's frankly shocking.
$1000, $500, $100, $50.... Those are just numbers TBH.... Let's see HOW you find these numbers instead of being generous while still guessing lower numbers.
I'm not saying the number in the article was wrong, i'm not saying $50 is wrong... I'm saying that, without any sources, $50 is just a number, it has no meaning whatsoever. As long as you're guessing, why not guess a transaction costs $0.005... Why is that guess worse than $50? I haven't seen any real calculations, my quick glance at the article made it look like the writer is just pulling numbers out of thin air, then proceeds to use them for a lot of calculations (full disclaimer: i just quickly scanned the article)...
Start with the current difficulty. Using this difficulty, you can get a rather good estimation of the current hashrate.
Then estimate the mix of ASIC's that would be needed to reach this hashrate. You'll have to get the biggest ASIC producer's numbers: how much of which model have been sold over the last 2-3 years?
Then, you'll have to find out where the biggest mining farms are located: are they using "leftover" energy produced by hydropower (energy that would otherwise go to waste) or are they using energy produced by burning coal, or maybe something in between?
What happens with the leftover energy? Is it recuperated? How about old ASIC's, are they being recycled?
Then, you'll have to study FIAT: how much trees are cut down, how much cotton, how much energy is used in the process of transporting raw materials, making paper, printing paper, distributing, running bank offices, making vaults, filling ATM's.
Then, look into the server parks that are needed by big banks...
Then, you'll have to find a way to compare FIAT energy costs with BTC transaction costs... The amount of FIAT being exchanged for goods and services on a daily basis VS the amount of BTC being exchanged on a daily basis, and their respective energy costs.
Finding an exact answer to this question is probably complex enough to fill a 4 year phd program, so i'm not even going to try a back-of-a-napkin estimation