I recently changed my 3 hard drives combo to just one. Purchased a WD Black 640GB as replacement. I went on two power calculting website to figure out how much power i would save in getting rid of 2 hard drives. Both sites gave me a result of 50 watts in savings. I don't really know if this is true or not. 25 watts per drive seems pretty darn high. Anyway, i'm pretty sure that i'll comsume less energy with only one hard drive.