* That's the threshold where you go from 128 to 256, not where you go from 64 to 128.

* If you're not going for the physically maximum overclock, the energy per bit is a lot less.

* That's for storing 512 byte blocks, so you'll run out of RAM bits 512 times sooner.

* Humans use about 10^20 joules of electricity per year.

* 10^20 joules at the cost in the link would be about 2^110 bytes, which is not all that far off.