As noted in a recent paper, 1 solar and wind energy can help to decarbonize electricity production but require other technologies, such as energy storage, to reliably meet demand. That paper estimates that energy storage capacity (capital) costs below $20 per kWh are needed to enable cost-competitive baseload power to be provided by renewable sources such as wind and solar power. Unfortunately, energy storage costs are estimated at around $400 or more per kWh for battery systems and on the order of $200 to $300 per kWh for pumped storage system.2 While battery storage costs are declining, it seems unlikely that they would decline to only 5% ($20/$400) of current costs in the foreseeable future. A possible solution lies in the use of conventional hydropower, operationally regulated to mesh with output from solar and wind facilities. This concept builds on an idea presented in the recent paper “Synergies of Hybrid Hydropower, Solar and Wind” (Donalek and Allen, HydroVision 2016) which describes how even modestly-sized hydropower reservoirs can cost-effectively act as energy storage facilities. To illustrate this approach, this paper examines use of conventional hydropower in conjunction with floating solar installations as pioneered by Ciel et Terre, the world leader in this technology. The concept we are describing works by ramping down conventional hydropower facilities (assets that are already economically supported based on their electricity generation and other benefits) when solar and/or wind output is substantial, and ramping up when this is not the case. Thus, additional costs for energy storage (in this case, in the form of water in the reservoir) are minor, and may be in the range required to support widespread adoption of solar and wind power. This paper examines several existing conventional hydropower facilities and provides estimates of additional energy that can be generated by adding a solar component, while in effect storing energy in the reservoirs for later use when the solar arrays are not producing power.