Sort of unrelated but, "According to my calculation, a single Bitcoin transaction uses roughly enough electricity to power 1.57 American households for a day." http://motherboard.vice.com/read/bitcoin-is-unsustainable I find this interesting thinking about Bitcoin as a currency. The first cryptographic currency example that I had read, from a cryptography book, didn't involve active power. I'm really surprised that B…
Each bitcoin block takes 25 BTC (11000 USD at time of writing) worth of electricity to mine, because that is the maximum that the sum total of miners can afford to spend and still break even. Currently it's only possible to fit somewhere around 2000 transactions in each block, because there is a hard-coded limit on the size of a block (1 MiB). So each transaction costs 11000/2000=5.5 USD, which is indeed the approxim…
No, each transaction costs at most $5.50 USD. You haven't established any lower bound in your calculations. A better approach would be to calculate the average number of hashes required to mine a block and the power efficiency of the latest generation ASIC miners.
Also, for what it's worth, $5 is much cheaper than a Western Union or SWIFT wire transfer so even this upper bound doesn't mean Bitcoin is uneconomical compared to modern banking.