Siting Optimization of In-stream Hydrokinetic Turbines within Hydropower Tailrace Channels*

Hydrokinetic energy is a renewable energy source currently attracting attention from funding agencies and developers across the United States. Recently, interest has been given to deploying hydrokinetic energy devices, also known as current energy converters (CECs), within tailrace channels downstream of conventional hydropower plants, where favorable siting and operational conditions exist. However, beyond the economic, environmental, and technical challenges, in-stream turbine deployment may reduce the hydraulic head available for upstream hydropower production, causing a reduction in hydropower generation. Under simplified assumptions, we present a one-dimensional momentum balance approach to analyze the backwater rise as a function of the hydraulic parameters and device characteristics. Model results were validated against three previous laboratory and field measurements at different scales. Based on the analysis, deploying a CEC device too close to the upstream dam would likely induce hydropower losses that outweigh the hydrokinetic gain, resulting in a negative net system power production. However, this can be avoided by deploying the turbine sufficiently downstream to let the backwater effect recovers to the upstream undisturbed water level. Combining the traditional backwater equation for open channel flows, an optimized siting distance can be computed to maximize the net power production while remaining within the tailrace boundaries to capitalize on its engineered channel, predictable outflows, and proximity to grid interconnection. This study presents the preliminary proof of concept for future designs of the hydrokinetic system in tailrace channels.