Energy

The oceans are a basis, or may be in the future, for producing several types of energy: wave, ocean thermal, other marine and hydrokinetic energy, offshore wind, oil and gas, methane hydrates, and hydrothermal sea vents.

Ocean Energy

Here, we consider the production potential for ocean energy. See also our broader analysis of the topic.

Production potential for MHK technologies worldwide and in the United States. World figures are from Helfer et al. ¹ and Stenzel and Wagner ² for osmotic power, Stenzel and Wagner ² for osmotic power with ecological constraints, IRENA ³ for tidal, Lockheed Martin ⁴ for OTEC, Minerals Management Service et al. ⁵ for marine current, and Pelc and Fujita ⁶ for wave. US figures are from the Electric Power Research Institute ⁷ for river current, Georgia Tech Research Corporation ⁸ for tidal stream, Lockheed Martin ⁴ for OTEC, the US Department of Energy for wave energy in the Continental US, and the Wave Power Technologies Office ⁹ for overall wave potential. Theoretical production assumes the technology is fully developed and ignores economic constraints.

Offshore Wind

The wind tends to be stronger and more reliable offshore, and in some areas, the water might be the only location for turbines. Offshore wind is growing rapidly, but is only 5% of wind energy and 0.25% of world electricity as of 2018 ¹⁰.

Source: Global Wind Energy Council ¹¹.

Costs

Since 2015, offshore wind has outperformed expectations. As of 2017, offshore wind bids in the Netherlands and Denmark came in as low as 7-8 ¢/kWh, though prices in the UK generally remained above 15 ¢ ¹². In the early 2020s, several macroeconomic factors caused the price to rise from 8.5 ¢ in 2021 to 14 ¢ in 2023, with a projected price of 8.5 ¢ in 2030 ¹³. The cost projections of a 2023 Department of Energy report ¹⁴ that the price might reach 5.1 ¢ for fixed bottom turbines and 4.5 ¢ for floating turbines does not appear to be realistic, nor do the projections of 30 GW of offshore wind capacity by 2030 and 110 GW by 2050 ¹⁵.

Types of Offshore Wind

The challenges of engineering structures in the water add to the cost. Most offshore wind resource is found at farther and deeper sites, where the logistics are more difficult ¹⁶. Improved turbine foundations are needed to harvest the abundant deepwater resources ¹⁷.

The two types of offshore wind are fixed-bottom turbines, which are most common today, and floating turbines. The latter are necessary to harvest wind resources far from the coast. As of 2024, floating offshore wind was at an infeasibly high cost of 29 ¢/kWh, but the cost may decline in the coming decades and deployment rise ¹⁸.

Oil and Gas

Oil produced from the ocean (offshore) tends to have lower greenhouse gas emissions.

Source: ¹⁹. Only upstream emissions, or emissions from production (not combustion) of oil are assessed. Figures are global averages and vary greatly by well.

However, recent research has found that emissions of methane, a potent greenhouse gas, may be twice as high for shallow offshore oil than previously believed ²⁰, and higher than that of onshore oil.

Methane Hydrates

Methane hydrates, also known as methane clathrates or "flammable ice", are highly pressurized crystals of methane trapped in ice. They are typically found in sedimentary deposits on the ocean floor and in the permafrost. The methane hydrate resource is twice that of all other fossil fuels combined ²¹. Recoverable reserves may be as high as 20,000 trillion cubic meters, over 4000 years at current gas production rates ²².

Reserves of methane hydrates and other fossil fuels. See ²² for information about hydrates and our production potential exhibit for other fossil fuels.

So far, there is no commercial methane hydrate production, and there are major engineering challenges to be overcome. There are three main proposed production methods: thermal stimulation, depressuration, and chemical inhibition ²³, and there are major field tests under way in the United States ²² and Japan ²⁴. The Chinese government has also demonstrated methane hydrate production in 2017 and is attempting to commercialize the technology in the disputed South China Sea, but commerical production will probably not be under way before 2030. The cost may be $3.50-4.00 per million cubic feet more than conventional sources, or a bit more than double recent prices ²⁵.

It may be possible to recover methane hydrates by injecting CO₂ into the hydrate, which extracts the methane and allows the hydrates to function as a carbon sink ²⁶. However, as methane is a potent greenhouse gas, methane leakage could negate this environmental benefit. The possible leakage of large quantities of hydrate is an unlikely but serious climate change risk.

Hydrothermal Sea Vents

Usable energy might also be extracted from hydrothermal vents on the sea floor. Although hydrothermal vents are ecologically sensitive, it should be possible to harvest energy without physically touching the vent ²⁷. The Maritime Applied Physics Corporation has demonstrated energy production from a hydrothermal vent ²⁸, as has a Japanese research team ²⁹, and Marshall Hydrothermal is developing a combined system of energy production, deep sea mining, and desalination ³⁰. However, full commercialization is not close, and data on the economic potential of hydrothermal vents is limited. To help spur the development of the technology, one possible early application is charging of unmanned naval vehicles ³¹.

We estimate the expected benefit of a hydrothermal sea vent research program to be about $3.7 billion and the expected cost to be about $21 billion. The levelized cost of hydrothermal sea vents has been estimated at 7.7 or 11.1 ¢/kWh ³²; for this calculation we take the midpoint of 9.4 ¢kWh. We also assume that only 20% of the electricity market can be served by sea vents, as the site must be near the coast and also near a vent. As hydrothermal sea vents are far from commercialization, we assume that it will take 25 years, at at cost of $830 million per year, the same as a proposed wave energy program. See our analysis of research and development for more information.

Feared risks of methane hydrates are that mining hydrates could destabilize the sea floor, causing a landslide or a tsunami, or that disturbance of hydrates could cause a large release of methane, exacerbating global warming, but experts now generally discount these risks ³³. The risks of methane hydrate extraction are comparable to those of conventional natural gas ³⁴.

Artificial Islands

Artificial floating islands are proposed for several energy purposes. A $34 billion, 5 GW extendable to 12 GW, offshore energy hub is under construction off the coast of Denmark ³⁵, scheduled for completion in 2033 ³⁶.

Energy islands have been proposed for ocean thermal power ³⁷ and for solar power to manufacture methanol ³⁸. Additionally, an artificial island to host transmission infrastructure has been found to be more economical for offshore wind farms than connected each offshore turbine individually ³⁹.