Vastly more costly than pumped water, high upkeep costs.<p>Does have relatively high efficiency though.<p>PS: &quot;Cost comparisons with pumped hydro are difficult, he said, because there are so few projects and not many data points.&quot; Is pure BS, here is someones coursework on the subject:  <a href="http:&#x2F;&#x2F;large.stanford.edu&#x2F;courses&#x2F;2014&#x2F;ph240&#x2F;galvan-lopez2&#x2F;" rel="nofollow">http:&#x2F;&#x2F;large.stanford.edu&#x2F;courses&#x2F;2014&#x2F;ph240&#x2F;galvan-lopez2&#x2F;</a>