I love this quote: Hydro pumped storage is “astoundingly efficient…In this future world where we want renewables to get 20%, 30%, or 50% of our electricity generation, you need pumped hydro storage. It’s an incredible opportunity.” – U.S. Energy Secretary Dr. Steven Chu in 2009. Still true today.

And actually, we think that 80-85% round trip is more accurate for our projects because we'll use the latest/greatest tech (variable-speed reversible francis style pump/generator turbines). I think the 70% from these figures is citing older projects with pump/turbines that were not quite as efficient.