OTEC and salinity power: Impact on the biosphere
Giant intakes, cold discharges and what they mean for sea life
What this tab covers Effects on human, animal, plant, fungal and microbial life and on whole ecosystems: in the short term (construction and early years), medium term (operating life) and long term (decommissioning and legacy).The main concerns are the very large water intakes and discharges: organisms caught on screens, nutrient-rich cold water released near the surface, and chemicals used against fouling. Experience is limited to small pilots.
Discharge depth that avoids affecting the upper 40 m (DOE model) 70 m or deeper1 Water or salt consumed by salinity plants None2 Life-cycle emissions, 1 MW hybrid OTEC (prediction) 71.5 g CO2e/kWh5Effects over time
| Life affected | Short term | Medium term | Long term |
|---|---|---|---|
| Humans1 | Little evidence of effect. | Plants can supply fresh water and cooling to islands, and avoid fuel imports. | Little evidence of effect. |
| Animals1910 | Construction disturbance at pipe routes. | Fish and plankton trapped on intake screens or drawn through the plant; pumps may disturb marine mammals; salinity plant intakes pose similar risks. | Little evidence of effect. |
| Plants1 | Little evidence of effect. | Warm or nutrient-rich discharge could cause algal blooms. | Little evidence of effect. |
| Fungi and soil life1 | Little evidence of effect. | Little evidence of effect. | Little evidence of effect. |
| Ecosystems1911 | Small footprint at pilot scale. | Discharge could change local temperature, nutrients and salinity, and upwelled cold water poses unknown risks to seabed and deep-water organisms; biocides are used against fouling. | Large-scale OTEC could alter ocean thermal structure; only modelled. |
How the effects are reduced
Discharging cold water below the thermocline, intake screens and low intake velocities, fencing against fish entrapment, careful biocide dosing, and mechanical pre-treatment or fouling-resistant membranes for salinity plants.
Sources
- Ocean Thermal Energy Conversion: Technology Brief IRENA, 2014
- Salinity Gradient Energy: Technology Brief IRENA, 2014
- Prediction of emission intensity for 1 MW onshore H-OTEC in Malaysia (Phua et al., Grand Renewable Energy proceedings) J-STAGE, 2022
- Ocean Thermal Energy Conversion (OTEC) Environmental Impacts (fact sheet based on NOAA material) PNNL Tethys
- Potential local environmental impacts of salinity gradient energy: A review (Seyfried, Palko and Dubbs, Renewable and Sustainable Energy Reviews 102) Elsevier, 2019
- OES-Environmental 2024 State of the Science Report, Chapter 11: Summary and Path Forward PNNL / Ocean Energy Systems, 2024