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Impacts Study of OTEC Seawater Effluent Discharge

Date: November 01, 2013 at 10:36 GMT

Ocean Thermal Energy Conversion (OTEC) seems to be an inexhaustible source of renewable energy if we consider that more than half of the solar radiative energy heating the Earth is stocked in the ocean. Technological constraints, associated with low process efficiencies, combined with estimates of ocean turnover rates suggest instead that OTEC could produce as much as 10 TW (1 TW = 1012 watts). This still represents about twice mankind’s electricity consumption predicted for Year 2040. But this figure does not take into account the possible degradation of the oceanic thermal structure and the biological perturbations induced by massive sea water intakes and effluent discharge, the latter having a temperature and chemical composition different from ambient values depending on the depth of discharge. Such an important limitation, known as the “impacts of artificial upwelling”, leads to a maximal sustainable OTEC power production of 3 to 5 TW, according to simple one-dimensional models. This theoretical estimate should be evaluated more precisely in consideration of local constraints and of a number of parameters like the scale of OTEC operations (overall power generation capacity), the spatial distribution of power plants and the effluent discharge strategy. In the latter case, multiple choices are available and environmental responses will vary according to the depth at which effluents are released, mixed or not. It is therefore critical, using various modeling tools, to carefully evaluate impacts from OTEC seawater intakes and effluent discharge under various scenarios in order to simultaneously optimize OTEC power production and minimize its potential disruption of the ocean environment. A positive impact of these “artificial upwellings” on the oceanic biological productivity should also be studied by coupling biological models with ocean-atmosphere physical models. 

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