# OTEC and salinity power: Impact on the biosphere

Giant intakes, cold discharges and what they mean for sea life

Source page: https://www.materialinsights.org/energy/e_otec/biosphere/

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 deeper^[1](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2014/Ocean_Thermal_Energy_V4_web.pdf) Water or salt consumed by salinity plants None^[2](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2014/Salinity_Energy_v4_WEB.pdf) Life-cycle emissions, 1 MW hybrid OTEC (prediction) 71.5 g CO2e/kWh^[5](https://www.jstage.jst.go.jp/article/gre/2/0/2_43/_article/-char/en)

#### Effects over time

| Life affected | Short term | Medium term | Long term |
|---|---|---|---|
| **Humans**^[1](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2014/Ocean_Thermal_Energy_V4_web.pdf) | Little evidence of effect. | Plants can supply fresh water and cooling to islands, and avoid fuel imports. | Little evidence of effect. |
| **Animals**^[1](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2014/Ocean_Thermal_Energy_V4_web.pdf)^[9](https://tethys.pnnl.gov/sites/default/files/publications/environmentalfactsheet.pdf)^[10](https://ideas.repec.org/a/eee/rensus/v102y2019icp111-120.html) | 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. |
| **Plants**^[1](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2014/Ocean_Thermal_Energy_V4_web.pdf) | Little evidence of effect. | Warm or nutrient-rich discharge could cause algal blooms. | Little evidence of effect. |
| **Fungi and soil life**^[1](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2014/Ocean_Thermal_Energy_V4_web.pdf) | Little evidence of effect. | Little evidence of effect. | Little evidence of effect. |
| **Ecosystems**^[1](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2014/Ocean_Thermal_Energy_V4_web.pdf)^[9](https://tethys.pnnl.gov/sites/default/files/publications/environmentalfactsheet.pdf)^[11](https://tethys.pnnl.gov/sites/default/files/publications/SOS_9.16.2024_Chapter11.pdf) | 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

1. [Ocean Thermal Energy Conversion: Technology Brief](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2014/Ocean_Thermal_Energy_V4_web.pdf) IRENA, 2014
2. [Salinity Gradient Energy: Technology Brief](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2014/Salinity_Energy_v4_WEB.pdf) IRENA, 2014
3. [Prediction of emission intensity for 1 MW onshore H-OTEC in Malaysia (Phua et al., Grand Renewable Energy proceedings)](https://www.jstage.jst.go.jp/article/gre/2/0/2_43/_article/-char/en) J-STAGE, 2022
4. [Ocean Thermal Energy Conversion (OTEC) Environmental Impacts (fact sheet based on NOAA material)](https://tethys.pnnl.gov/sites/default/files/publications/environmentalfactsheet.pdf) PNNL Tethys
5. [Potential local environmental impacts of salinity gradient energy: A review (Seyfried, Palko and Dubbs, Renewable and Sustainable Energy Reviews 102)](https://ideas.repec.org/a/eee/rensus/v102y2019icp111-120.html) Elsevier, 2019
6. [OES-Environmental 2024 State of the Science Report, Chapter 11: Summary and Path Forward](https://tethys.pnnl.gov/sites/default/files/publications/SOS_9.16.2024_Chapter11.pdf) PNNL / Ocean Energy Systems, 2024

## Other sections

- [Summary](https://www.materialinsights.org/energy/e_otec/index.md)
- [Overview](https://www.materialinsights.org/energy/e_otec/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_otec/correlation/index.md)
- [Efficiency](https://www.materialinsights.org/energy/e_otec/efficiency/index.md)
- [Techniques](https://www.materialinsights.org/energy/e_otec/techniques/index.md)
- [Resources and labour](https://www.materialinsights.org/energy/e_otec/resources/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_otec/links/index.md)