Salinity gradient: Abundance
Terawatts on paper, pilot plants in reality
What this tab covers How much of this energy there is: the natural flow or stock, the share that could be harnessed, and how much is used today, compared with world primary energy use (592 EJ in 2024).A few terawatts in theory, but far less once river ecology and plant practicality are counted; today only pilot plants exist.
A flow: renewed continuouslyHow much there is
| Measure | Value | Compared with world energy use | Note |
|---|---|---|---|
| Global theoretical potential (oceans and seas) | 3.1 TW (IRENA table: 3,158 GW gross, about 27,700 TWh per year)1 | about 17% of world primary energy use (98 EJ vs 592 EJ) | IRENA elsewhere cites 3.4 TW. |
| Global technical potential | 647 GW (5,177 TWh per year)1 | about 3% of world primary energy use (18.6 EJ) | IRENA's 5,177 TWh/yr implies about 590 GW of average output; at the full 647 GW year-round it would be about 20 EJ (3.4%). |
| Extractable potential at river mouths (latest reassessment) | 399 GW3 | about 2% of world primary energy use (12.6 EJ) | 5.6 times the 2016 estimate, using larger discharge and satellite salinity datasets. |
| Practical potential at river mouths (2016 estimate) | 625 TWh per year2 | about 0.4% of world primary energy use (2.25 EJ) | After physical and environmental constraints; theoretical river-mouth potential 15,102 TWh/yr. |
| Output of Japan's first osmotic power plant (Fukuoka, 2025) | 880,000 kWh per year (expected)8 | negligible | Mixes concentrated seawater from a desalination plant with treated sewage water; began operating 5 August 2025. |
The spread of estimates comes down to how much river water a plant may divert. A river mouth only releases its gradient once, and a plant that took the whole flow would alter the estuary, so practical studies cap the share used. That is why the 2016 practical estimate (625 TWh/yr) is about 4% of the theoretical river-mouth figure, while a 2026 reassessment with better river and salinity data raised the extractable figure to 399 GW.
Measured against world primary energy use of 592 EJ in 2024 (Energy Institute Statistical Review 2025), even the technical potential is about 3%. Actual use is limited to demonstrations: Statkraft's 10 kW Tofte prototype in Norway (2009-2013), REDstack's 50 kW pilot on the Afsluitdijk in the Netherlands (2013), Sweetch Energy's OPUS-1 on the Rhône (testing from late 2024) and the Fukuoka plant in Japan.
Sources
- Salinity Gradient Energy: Technology Brief IRENA, 2014
- Practical global salinity gradient energy potential (Alvarez-Silva, Osorio and Winter, Renewable and Sustainable Energy Reviews 60) Elsevier, 2016
- Extended assessment of the globally extractable salinity gradient energy from river mouths (Alvarez-Silva, Roldan-Carvajal and Arevalo, Sustainable Energy Technologies and Assessments 91) Elsevier (via PNNL Tethys), 2026
- Japan's first osmotic power plant begins operations in Fukuoka Japan Science and Technology Agency (Science Japan), 2025