Energy Sources: Geothermal and Marine
These two forms of energy symbolically represent two of the basic elements of nature: fire and water.
Geothermal energy is the surface manifestation of Earth’s internal heat. It is harnessed through the direct use of hot water or the production of electricity via steam turbines. Just under 90 countries across the world use their geothermal resource: almost all use it directly (global installed capacity for direct use amounted to about 108 GW), while only a third use it for electricity generation (equivalent to about 16 GW of installed capacity worldwide).
The energy of the waves, currents and tides is generated respectively by wind on the sea’s surface, by the temperature and saline gradients of the seas and by the gravitational action of the Earth-Sun-Moon. The systems to recover energy are ingenious and harness all movements of the water masses: some of them are also combined with offshore wind and/or floating solar PV. Marine energy technologies are mostly still in developmental stages and have not reached full commercialisation, with a global cumulative installed capacity of just over 520 MW.
- EIA (US Energy Information Administration), International Energy Statistics [Last accessed 25 January 2023];
- IEA (International Energy Agency), World Energy Outlook 2022;
- IEA-OES (International Energy Agency - Ocean Energy Systems), Annual Report: An Overview of Ocean Energy Activities in 2021;
- IRENA (International Renewable Energy Agency), Ocean Energy Technology Brief • Renewable Energy Statistics 2022 [Last accessed 25 January 2023];
- Lund and Toth, Direct Utilization of Geothremal Energy 2020 Worldwide Review, Geothermics 90, Elsevier (2021);
- REN21, Renewables 2022 - Global Status Report