There are well over 100 conceptual designs for converting the energy of waves, river and tidal currents, and ocean temperature differences into electricity. Most of these ocean energy and hydrokinetic renewable energy technologies remain at the conceptual stage and have not yet been developed as full-scale prototypes or tested in the field. Consequently, there have been few studies of their environmental effects. Most considerations of the environmental effects have been in the form of predictive studies and environmental assessments that have not yet been verified. While these assessments cannot predict what if any impact a given technology may have at a given site, they have been instructive in identifying several common elements among the technologies that may pose a risk of adverse environmental effects:
- Alteration of current and wave strengths and directions
- Alteration of substrates and sediment transport and deposition
- Alteration of habitats for benthic organisms
- Noise during construction and operation
- Generation of electromagnetic fields (EMF)
- Toxicity of paints, lubricants, and antifouling coatings
- Interference with animal movements and migrations, including entanglement
- Strike by rotor blades or other moving parts
In the case of ocean thermal energy conversion technologies, additional potential effects stem from the intake and discharge of large volumes of sea water; changes in temperatures, nutrients, dissolved gases, and other water quality parameters; and entrainment of aquatic organisms into the intake and the discharge plume.
Although there have been few environmental studies of these new energy conversion concepts, a preliminary indication of the importance of each of the environmental issues was gained from published literature related to other technologies (e.g., noises generated by similar marine construction activities, EMF emissions from existing submarine cables, environmental monitoring of active offshore wind farms, and turbine passage injury mechanisms examined for conventional hydropower turbines). Experience with other similar activities in freshwater and marine systems has also provided information about impact minimization and mitigation options applicable to these new renewable energy technologies.