In a first stage they want to build 10MW of capacity until 2015 and are planning to build one up to 50MW facility.

You probably might not know this but assuming exponential difficulty growth is obviously a fallacy (aslong as there isn´t exponential price increase in Btc).

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.


Regardless, compared to my example, Difficulty could increase atleast 171 fold before being the same amount that can easily be saved by some energy efficient appliances in the household in the US alone.
It really is a TINY usage compared to wasteful electricity usage in the US, let alone globally.