So they aren't living long enough to make up for their own cost to the environment. They are a child's toy, a pipe dream for free energy.:

"And, of course, tall, string towers require a lot of construction materials that have (ahem) a considerable carbon footprint to create.  Compared to the amount of "carbon free" electricity generated, the carbon emitted in manufacturing and construction of the towers may take many years to counterbalance.  Consider that the relatively low electricity production of each tower (compared to a coal or nuclear fired plant) means that far more power transmission lines must be constructed, and there is a carbon footprint involved, not to mention the excess demand created for copper, which has its own environmental issues in mining and refining, and the problems with meeting demand when creating new copper mines hits a high wall of resistance from the very same environmentalists who think windmills are a solution to the problems they imagine CO2 creates."