April 27, 2024: Ocean Energy
Good evening. Last week, in discussing geothermal energy, I mentioned how ocean energy is confined to the “Other” category in the Energy Institute Statistical Review of World Energy, and how that might be a good topic for another day. Now it is another day. For today, I would like to make a quick and broad overview of the subject, and many things that I will touch on today are worthy of a deeper look. For today’s purposes, “ocean energy” is an energy source that, somehow or another, is derived from the motion of ocean water.
Even though ocean energy is a niche energy source, like geothermal, the history of ocean energy goes back farther than one might think. In The Medieval Machine, Jean Gimpel documents a kind of proto-industrialization in High Middle Ages Europe, centered in France. Among the proto-industrial technologies in use at the time were water mills and tidal mills, which used the flowing of water to power mechanical processes, especially the grinding of grains. Watermills, along with windmills, which were another medieval introduction, were among the first technologies that granted humans power sources other than muscles.
According to this, the earliest excavated tidal mill dates to Northern Ireland in the year 619. Tidal mills function by filling a storage pond when the tides come in, and when the tides go out, the water receding from the pond powers a water wheel. Medieval tidal mills were not used to generate electricity of course, but otherwise the principle of operation was not substantially different from that of a modern tidal power plant.
The first hydroelectric power plant was built in Northumberland, England in 1878, and several more followed in the United States in the 1880s, including the Niagara Falls plant in 1881. The first hydroelectric power plant for public power was built in 1882 in Wisconsin, the same year as Thomas Edison’s Pearl Street Station, which was the first public power plant of any sort.
According to Brian Potter’s excellent review of electric grids, hydroelectricity (34%) and coal (56%) were the major sources of electricity in the United States by 1930. That was down to 6.2% by 2022. The 1930s brought about monumental hydropower construction in the United States, including Hoover Dam and Grand Coulee Dam. According to Wikipedia, the world’s largest power plant by capacity is the Three Gorges Dam, which went operational in 2012 on the Yangtze River in China. All seven of the top seven power plants by capacity are hydro, and four of them are in China.
Given the successful history of hydropower in the 20th century, and given the vastly greater energy potential in the oceans compared to rivers, it is tempting to look to the ocean for an energy solution in the 21st century.
We’ll start with wave energy. Efforts to harness the kinetic energy of ocean waves go back to the first patent in 1799, the first wave-powered electrical generator in 1910, and early commercialization efforts in the 1960s. However, it was the energy crisis in the 1970s that most spurred interest. Interest fell in the 1980s with receding oil prices, but it picked up to a moderate level in the 21st century.
Estimating how much wave energy could be harvested is tricky. In the exclusive economic zone (EEZ) of the United States, one estimate of the theoretical wave energy source is 3,300 terawatt-hours (TWh) per year, which compares to 4548 TWh U.S. electricity demand in 2022. Of that, 2,000 TWh are in Alaska, and the majority of the remainder is on the West Coast of the United States and Hawaii. The theoretical resource is all the energy that contained in ocean waves. Of that, a subset is the technical resource, which is all the energy that could be captured from existing technology. And of that, a subset is the practical resource, which is all that which could be captured from existing technology, taking external constraints into account. The same paper estimates 50-200 TWh as the practical wave energy potential in the United States, which is about 1-4% of electricity demand. Note that any waves outside of a country’s EEZ are probably not practical.
This doesn’t sound like much, though maybe the numbers could improve a bit with better technology. Wave energy is more stable and more predictable than solar or wind energy, and so even a small amount could be a useful stable electricity source in a high-renewable grid. Though I would put my money on nuclear or geothermal to fill that role.
Worldwide, one estimate of the potential resource is 29,500 TWh, which is roughly equal to world electricity demand in 2022. I haven’t been able to find a good estimate of the practical world potential, but it wouldn’t surprise me if that too was about 10% or less of the theoretical potential, and it may too have the problem of not being colocated well with demand.
I won’t go into detail about the various types of wave energy converters, but there are quite a few. A recent survey of experts from the National Renewable Energy Laboratory found that at present (2020), wave energy converters have a levelized cost of electricity of around 35-85¢/kWh. That could be reduced to 7±3¢/kWh in an optimistic scenario by 2050 and 13±6¢/kWh in a pessimistic scenario. By comparison, the LCOE of natural gas in the United States was 5.6¢/kWh in 2019. In short, wave energy is not even close to being economically competitive today, and it could be by midcentury under the most optimistic scenarios.
Under normal circumstances, the motion induced by ocean waves is harsher and poses a greater engineering challenge than that of river currents for a hydroelectric generator. On top of that, the devices have to survive corrosive salt water and storms. There are also the practical issues of competition with fishing and navigation. For these reasons, there is still not any commercial wave energy beyond some demonstration projects.
Here’s a report from 2012 that, rather optimistically, argues that with less than $10 billion of R&D and federal subsidies, wave power could reach an economically competitive level in Alaska, which has expensive electricity due to its remoteness. After that, wave will ride the cost reduction curve of learning-by-doing and expand to its full potential. This argument looks like a good example of how learning curves can mislead if not used carefully. I am working on a larger project now on the use and abuse of learning curves in energy policy, and I plan to say much more about that later on.
Tidal power derives energy from the flow of water from tides. As with wave energy converters, there are many types of tidal devices. Unlike with wave, there does exist a commercial tidal energy energy market, albeit a niche market of 0.127 TWh in 2022.
As with wave, the potential for tidal energy is hard to measure as well. Market potential has been estimated at 150-800 TWh per year, with the larger value being around 3% of world electricity consumption. This limited number results from the special geographic conditions required for an effective tidal generator, typically an estuary with sufficiently fast water motion. These same conditions are also associated with especially biologically sensitive areas. Tidal power suffers from the same corrosion and biofouling issues that afflict wave power. Early commercial tidal projects are estimated to have an LCOE of 13-28¢/kWh, with a 61% reduction for a mature industry. Again, it will become an economically viable industry only under optimistic projection.
Ocean thermal energy conversion (OTEC) harnesses energy from the temperature gradient of the ocean, with warmer water near the surface and cooler water at depth. For this reason, OTEC works best at tropical latitudes and poorly at equatorial latitudes. The principle is a lot like geothermal energy, except it is on the ocean instead of land.
World OTEC technical potential is estimated at 9.3 TW, which at a 95% capacity factor is over 77,000 TWh, enough to meet all the world’s electricity needs more than twice over. This paper models potential LCOE around the world and finds that, at the best sites near the equator, the potential LCOE is 13.2¢/kWh.
It is hoped that OTEC will find a niche in equatorial island markets with expensive electricity. There are also some coproduct opportunities, such as cool seawater air conditioning (SWAC) and pumping of fresh deepwater for agricultural applications. This attempt to argue for OTEC’s potential on the basis of island markets and coproducts comes across to me as very hand-wavy.
OTEC was first trialled in 1881, and over the years there have been various attempts at demonstration projects, but to date there is no OTEC industry to speak of. In 2020, 19.8% of electricity in the United States came from renewable energy sources. That isn’t too far from the 14.4% that was projected for 2020 in the 1979 Annual Energy Outlook from the Energy Information Administration, the first such outlook from what was then the new Department of Energy. However, the EIA envisioned that OTEC would comprise almost 10% of that renewable energy, and they also thought that geothermal would produce more than three times as much energy as solar. It is a good reminder to be humble about long-term energy projections.
Ocean currents are driven by wind, temperature differentials, earthquakes, storms, and the Coriolis force from the rotation of the Earth. These currents are another potential energy source, with a potential of around 5 TW. Since ocean currents are highly predictable and stable, a 70% capacity factor is predicted, which means that ocean current should, in theory, be enough to meet the world’s electricity demand, albeit barely.
This paper gives an LCOE of 24¢/kWh, once again too high to be practical. As before, ocean current power is at the prototype phase, such as the recent 100 kW Kairyu machine off the coast of Japan. IHI, the company behind Kairyu, hopes to deploy a 2 MW machine by 2030 which maybe will be economically competitive with other electricity sources. We shall see.
Osmotic power, also called salinity gradient power, is generated when fresh river water mixes with salty ocean water at the mouth of a river. It works a bit like desalination in reverse, as desalination entails an energy input to separate salty brine from fresh water. There are a few technologies for doing so; I think pressure retarded osmosis is one that is most favored now. Here is an explanation.
The global potential for osmotic power is estimated at 1700 TWh, which is about 6% of world electricity. Like tidal power, osmotic power is limited geographically to areas that are sensitive ecologically.
As usual, osmotic power is at a prototype and demonstration phase. A few years ago, a study found that an osmotic power plant, built with today’s technology, would have an LCOE of around 20¢/kWh, and this might be reduced to 10¢/kWh with foreseeable improvements. It would be baseload power. Such a cost would be high but not outrageous. The development of new membranes appears to be the most important technological challenge currently.
I think that’s enough for now. As we have seen here, there are at least five plausible ways in which energy could be derived directly from the oceans. There are several indirect possibilities too, such as the struggling offshore wind sector and offshore drilling of oil. There are methane hydrates, a form of pressured natural gas on the seabed with potentially vast reserves. Uranium from seawater looks realistic and could provide many times the uranium that the nuclear power industry could realistically need. There is the idea of floating solar islands, which would address solar’s high land use needs. Electricity could be harvested from seabed hydrothermal sea vents. Seaweed is a potential source of biomass that might circumvent the land use and associated environmental impacts of terrestrial biomass.
However, none of the ocean energy options look too terribly promising as a large-scale energy solution. Tidal and osmotic power would have too limited a practical potential, and wave power is questionable. None of the five options look like they will be cost-feasible in the foreseeable future, if ever. I’m all for spending some resources on unorthodox ideas, but subject to realistic expectations.
Quick Hits
Over the last week, pro-Palestinian protests started at Columbia University and spread like wildfire throughout the country, having also morphed at times into civil unrest. A few months ago, Ilya Somin wrote for Reason on the far left’s support for Hamas and the mindset that would motivate such a thing, though this article doesn’t go into the Marxist roots of earlier Palestinian nationalist movements (Fatah, the Democratic Front for the Liberation of Palestine, etc.), which I think would be valuable context. Most critics of Israel’s conduct in this war who I have talked to have insisted that they are anti-Zionist but not antisemitic; such a distinction seems to have been lost in the noise of the protests. Most political movements are vulnerable to abuse by malevolent actors, but it seems to me that antiwar movements are especially vulnerable. The parallels with certain factions uncritically adopting Kremlin talking points with regard to the Russian war in Ukraine should be obvious.
I wrote a bit about the nature of Hamas in a post shortly after the outbreak of the war. It remains my view that Hamas is entirely untrustworthy, and there is no credible solution to the conflict that does not entail the elimination of Hamas’ ability to launch an attack similar to that of October 7.
Seaver Wang and coauthors at The Breakthrough Institute have a new report on the mining requirements of various forms of energy. They find that coal requires the movement of far more material than any other mainstream electricity source on a per-GWh basis, followed by natural gas. Nuclear power requires less movement than renewable sources in general. These results are not a great surprise to those who have been following these issues for a while, but this report goes into greater depth and precision than others I have seen.
It has come to light that Robert Habeck, the German Minister for Economic Affairs and Climate Action and a member of the Green Party, has promoted falsified documents to justify that country’s disastrous nuclear phase-out of the last few years. Here is an analysis by Cicero, a German magazine (in German), and here is an English version. This seems like it should be a much greater scandal than the reporting so far suggests.
There is a newly public think tank called the Abundance Institute. There is also the new Inclusive Abundance Initiative. Are these the same things? I am confused. At any rate, I would characterize these as pro-technological progress initiatives, and in particular they respond to the doom and gloom that surround artificial intelligence and especially came into vogue last year. So far they are light on specifics. I am looking forward to seeing what comes of them.