Quote from: Collider on July 01, 2014, 06:44:57 AM

There is a very real limit to difficulty, and it is Btc price, power efficiency, power price, available hosting facilities, hardware price and some other factors.

The upper limit is calculated in this thread:

https://bitcointalk.org/index.php?topic=281279.0

Based on $100 per BTC and $0.10 per kWh the electrical cost break even point is about 179.7 PH/s.

Adjusting for $600 per BTC (x6) and $0.02 per kWh (x5) would give us 179.7 * 6 * 5 = 5,391 PH/s.

The same thread assumes 0.8 J/GH so:

   5,391 PH/s = 5.391 * 10¹⁸ H/s
   0.8 J/GH = 0.8 * 10^-9 J/H

   (5.391 * 10¹⁸ H/s) * (0.8 * 10^-9 J/H)

   = ( 5.391 * 0.8 ) * ( 10¹⁸ * 10^-9 ) ( H/s * J/H )

   = 4.3128 * 10^(18-9) (J/s)

   = 4.3128 GW

World power production from:

http://en.wikipedia.org/wiki/Electricity_generation

is about 2311.4 GW.

So Bitcoin would use about 0.1866 % of world electrical output in this maximum build out scenario.

BTW in the above scenario the difficulty would be 753,000,000,000