Modeling the energy yield enhancement from a wind turbine at a deep offshore low wind site through combined power and thermocline energy production

Abstract

This paper presents steady-state performance modeling and analysis of a novel wind powered system that concurrently exploits thermocline thermal energy through deep sea water extraction in conjunction with offshore wind energy for combined power and thermal energy production. A single offshore wind turbine rotor directly coupled to a large positive displacement pump is modeled to supply deep sea water at high pressure to a land-based plant, the latter consisting of a hydro-electric generator coupled to a heat exchanger. The steady-state power-wind speed characteristics for the system are derived from a numerical thermofluid model. The latter integrates the hydraulic characteristics of the wind turbine-pump combination and a numerical code to simulate the heat gained/ lost by deep sea water as it flows through a pipeline to shore. The model was applied to a hypothetical megawatt-scale wind turbine installed at a deep offshore low wind site in the vicinity of the Central Mediterranean island of Malta. One year of wind speed and ambient measurements were used in conjunction with marine thermocline data to esti- mate the time series electricity and thermal energy yields. The total energy yield from the system was found to be significantly higher than that from a conventional offshore wind turbine generator (OWTG) that only produces electricity. It could be shown that at sites having less energetic wind behavior and high ambient temperatures as a result of a hotter climate, the cooling energy component that can be delivered from such a system is relatively high even at periods of low wind speeds.