You can sort of ballpark the bitcoin energy usage by assuming all mined coins are sold at the current exchange rate, and used to buy electricity at a reasonable

You can sort of ballpark the bitcoin energy usage by assuming all mined coins are sold at the current exchange rate, and used to buy electricity at a reasonable average for the world... 12.5 BTC every 10 mins => 12.5 / 600 per second => 0.02083. 0.02083. * $600 = $12.5 / sec Assuming electricity cost of $0.10 per kWH... %12.50 / 0.10 = 125 kWh / sec. 125kWH * 3.6e6 joules, per second => 450 MW For comparison, the UK power grid runs at about 30-40GW.