Energy use can be computed from first principles given some arbitrary assumptions: average power per node and number of nodes. There are ARM nodes that require

Energy use can be computed from first principles given some arbitrary assumptions: average power per node and number of nodes. There are ARM nodes that require less than 10W. Then there are more conventional servers that require ...150W? Average here is pure guesswork, but error bounds aren't that large - let's say 100W/node. How many nodes are going to exist - I think 10k is a reasonable maximum number. The result is 24000kWh per day. At $0.15/kWh, that means $3600 in daily energy costs. There's also the hardware cost itself and internet connection cost (which can be zero if there's an already paid for connection) - but all in all, total, real expenses to run ethereum become a rounding error of current ones. Guesstimating hw depreciation and connection cost, daily total at $5k translates into $1.825M/year. The value of block rewards during the last 24h is ~$15M. In other words resources required for running ethereum for ~3 hours now are going to be enough to run it for a year after the merge.