Let's double that 100 watts to account for cooling, and calculate at fairly cheap electric rates of 5 cents per kwh (which is what a lot of industrial scale customers pay in much of the US) That adds up to 1 cent per hour. At 8760 hours a year, let's round up to $100/yr more to run the 8 TB drives. If we use very expensive 20 cent/kwh electricity (maybe it is that high in some EU countries?) and assume a five year life, that's $2000 more that the power and cooling costs for the 8 TB option. I imagine the 100 TB QLC drive will cost a lot more than $2000 more than 13 8 TB drives plus a shelf.
If your datacenter floor space is very limited, I suppose a 12.5x reduction in the amount needed for nearline storage could be worth something as well, but still not enough to make up the cost difference.