Hm, a 1TB hdd has an energy consumption of 5W. This would cost me around $1 per month to operate without any server infrastructure. Dont think that it is that easy to achieve ROI...
Well, don't use 5W HDDs then
There are plenty of 1-2W HDDs out there (5400rpm), and of course is more efficient to use HDDs of a capacity higher than 1Tb. And cheaper. Actually, best price per TB is achieved in 3Tb and 4Tb HDDs, and they consume the same energy as one of 1Tb