Bitcoin Network Power Consumption Estimate

First, note that Bitcoin mining efficiency does not matter when estimating the trend of the power consumption of the entire Bitcoin network.

The power consumption of the entire network depends on five things:
 
x = the exchange rate [USD/BTC]
e = the era [0..32]
f = the average fees per hour [BTC/hour]
c = the average cost of energy [USD/kWh]
r = the average percentage of income miners spend on energy [unit less ratio]

From the era we can calculate the average hourly BTC subsidy rate:
s = 6(50/2e) [BTC/hour]

And the average amount of BTC all the miners in the world make per hour:
b = s + f [BTC/hour]

From this we can calculate the amount of USD per hour all the miners in the world make:
u = bx [USD/hour]

Given the worldwide average percentage of income miners spend on energy the amount spent worldwide on energy is:
ur [USD/hour]

And finally, the worldwide power consumption is given by:
P = ur/c [kW]
   = bxr/c [kW]
   = (s + f)xr/c [kW]
   = (6(50/2e) + f)xr/c [kW]

Notice that mining efficiency does not enter into this equation and does not matter.

You do not need to know or estimate the average overall efficiency of the mining network unless you want to calculate the difficulty and/or hash rate.

Let’s put in some numbers:

x = $50,000; the exchange rate [USD/BTC]
e = 3; the era [0..32]
f = 5; the average fees per hour [BTC/hour]
c = $0.03; the average cost of energy [USD/kWh]
r = 0.8; the average percentage of income miners spend on energy [unit less ratio]

P = (6(50/2e) + f)xr/c [kW]
   = (6(50/23) + 5) 50000 ( 0.8 ) / 0.03 = 56,666,666 [kW] = 57 Gigawatts

World power production/consumption is about 15,000 Gigawatts.

Bitcoin mining will trend toward 57/15,000 = 0.38 % of world power production given these values.

This scales by BTC price so:

BTC at $500,000 means power consumption would trend to 3.8% of worldwide power.

BTC at $5,000,000 means power consumption would trend to 38% of worldwide power.