Chile: The world's green energy supplier by Valhalla

The idea of a water battery is really cool! however, I was wondering how the efficiency of the solar panel "system" is affected? solar panels already have a rather long period before a return is met on the initial investment. How will implementing this system increase/decrease that since it introduces two new conversions of energy (from electrical to the gravitational potential of the water tank, and then from the water to electricity again)? will the cost of the system and reduced efficiency be worth the benefits?