Now add in all the oil needed to mine the sand, rock, portland cement and the energy needed to cook the cement plus the transport costs for ALL the mined and refined materials and the whole concept fails.
Worst part is how all the big energy corps bailed in the first few years of operation selling to smaller energy corps who then went bankrupt to be bought up for pennies on the dollar by the big energy corps.
The circle jerk of modern 'economics'.