Comment by thescriptkiddie

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 approximate value of 1.57 days worth of average per household energy consumption in the US. This is a big reason why it is important that the 1 MiB limit is lifted soon, the artificial restriction on transaction volume pushes the cost per transaction far too high. As a side note, when the block reward halves to 12.5 BTC in a few months, we will either see the value of bitcoin double or the hashrate (and energy consumption) halve - probably a little of both.