Ocean Thermal Energy Conversion (OTEC) uses large flows of warm surface seawater and cold deep seawater to generate clean electricity. The tropical ocean at a typical OTEC site has two distinct layers: a warm surface layer with low nutrient levels, and a cold deep layer that is nutrient-rich. Introducing deep nutrients into the ocean’s sun-lit upper layers could potentially increase plankton growth or cause algal blooms. Thus, seawater discharged from an OTEC plant should be returned into the ocean deep enough so that these nutrients don’t trigger biological growth.
The U.S. Department of Energy has released a report describing the simulated biological impact from operating large OTEC plants. The study was performed by Makai Ocean Engineering under a cost-shared grant and can be downloaded here.
This new software is the most sophisticated tool for modeling OTEC’s environmental effects to date. When run with an OTEC plant, the model can determine the size, depth, and flows of the OTEC plant’s seawater discharges that would minimize plankton increases. In all cases modeled in Hawaiian waters, no increase in plankton levels occurred in the upper 40 meters (130 ft) of the ocean. From 40 to 120 meters (130 – 400 ft) OTEC-induced plankton growth is low and well within the naturally occurring variability. These results suggest that suitably designed large OTEC plants will cause no significant increase in biological growth. This model will be important to developers and regulators as commercial OTEC develops. A brief video illustrates earlier modeling work done with this program.