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Assessing the impacts of free-stream turbines for electricity generation

University of British Columbia

Due to a number of factors including energy security and climate change, there is an urgent need to transition the global energy supply to renewables. Two potential sources are tidal-stream and hydrokinetic power, utilizing free-stream water turbines as generating devices. Much of the interest in tidal-stream power comes from resource assessments that suggest that significant amounts of electricity could be produced from tidal currents flowing through straits. These assessments inventoried the kinetic energy flux and do not account for flow reduction due to turbine resistance. As such, they do not present a realistic picture of the resource. An analytical model for flow reduction in tidal straits demonstrates that only 38% of the natural fluid power is theoretically extractible. This model does not capture the behaviour of bays, lagoons, or the open ocean. Maximum power production requires flows to be reduced to 58% of natural and if the flow is kept above 95% of nominal (due to environmental regulations) less than 10% of the total power is available. A large laboratory experiment was built to test the analytical model and the results agree with the analytical model. Predicted future levelized cost of energy from tidal generation in straits is an interplay of reduced production due flow reduction competing with decreasing technology costs. This is modelled, indicating levelized costs of energy will drop initially, then rise due to flow reduction. Considering hydrokinetic power near hydropower stations, a 1D model used Seton Canal data to simulate the installation of turbines. The results show that the installation of hydrokinetic turbines would decrease the output of the existing powerhouse. Furthermore, the decrease in hydroelectric production is greater than the hydrokinetic production. Thus, installing hydrokinetic turbines would cause a net energy loss. In conclusion, there are three key recommendations: 1. Policy makers are cautioned in embracing tidal resource assessments that are based solely on kinetic energy flux. 2. Project proponents and regulators are advised to study far-field effects of any proposed free-stream turbine installation. 3. Developers, investors, and policy makers are cautioned towards assuming that the long-term cost of energy from tidal power will decrease.

Text

2015-10-24

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/54999

Civil Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/