Salinity gradient: Impact on nature
No burning, but estuaries could feel the intakes
What this tab covers What taking energy from this source does to land, water, air and climate, wildlife and ecosystems, with life-cycle emissions and land use where measured.No combustion and no consumption of water or salt, but large intakes and brackish discharges can disturb estuaries; impacts are so far inferred from pilots and from desalination plants.
Effects on nature
| Area | Effect | Size | How it is reduced |
|---|---|---|---|
| Air and climate | No NOx, CO or CO2 emitted in operation.1 | Zero operational emissions | None needed |
| Water | Neither water nor salt is consumed, but diverting river flow changes estuary mixing; effluent is brackish and of high volume.1 | Only a limited share of river flow can pass through a plant | Cap withdrawals; discharge design to avoid recirculation |
| Wildlife (intakes) | Intake of both fresh and salt water can impinge and entrain organisms.5 | Not yet quantified at pilot scale | Screens and low intake velocities, as for desalination plants |
| Chemicals | Pre-treatment against biofouling may add chemicals to discharges.5 | Not quantified | Mechanical pre-treatment, fouling-resistant membranes |
| Life cycle | Membrane manufacturing dominates impacts; eutrophication, ecotoxicity and carcinogenic impacts can exceed those of other renewables under some assumptions.6 | Impacts about 50% higher with natural water than with concentrated brine | Higher power density membranes; brine-based hybrids |
| Land | Plants can be built underground or in low buildings near the shore.1 | Small, not quantified | Use existing industrial or harbour sites |
Because no comprehensive environmental assessment of a working plant yet exists, most expected impacts are inferred from desalination plants and cooling-water intakes. The main concerns are local: entrapment of fish and larvae at intakes, chemicals used to keep membranes clean, and changes to salinity patterns where large volumes of brackish water are returned to the estuary.
A 2021 life-cycle study of reverse electrodialysis found its impacts comparable to, and often lower than, wind and solar under favourable conditions, but it did not publish a single figure in g CO2e/kWh, so none is given here.
Sources
- Salinity Gradient Energy: Technology Brief IRENA, 2014
- Potential local environmental impacts of salinity gradient energy: A review (Seyfried, Palko and Dubbs, Renewable and Sustainable Energy Reviews 102) Elsevier, 2019
- Life cycle assessment of salinity gradient energy recovery using reverse electrodialysis (Mueller et al., Journal of Industrial Ecology 25) Wiley (via PNNL Tethys), 2021