More than 90% of the heat from global warming has been absorbed by the ocean [1] and sea-surface temperatures reached a record high in the summer of 2023 [2]. While this is a crisis, it is also a massive opportunity. This heat can be used to power a new sustainable ocean economy with an offshore fleet of energy-independent, long-endurance, autonomous platforms that can be used to create new markets for energy generation, edge computing, satellite ground stations, carbon dioxide removal, intelligence, and research.
These platforms could be placed in the warmest parts of the ocean and can generate electricity using Ocean Thermal Energy Conversion (OTEC), which is not necessarily a new technology, but one that has the potential to reach cost parity with natural gas and petroleum [3]. In the simplest terms, OTEC works by using the temperature differential of sun-soaked surface water and near-freezing deep water to evaporate and condense a working fluid to spin a turbine and generate electricity. All of this, with zero emissions and numerous beneficial climate effects, potentially making it the world’s first source of carbon-negative electricity.
How OTEC Works (Source)
Current approaches to renewable energy generation are tailored to the land-based, grid-tied customer. Even in remote locations such as the Hawaiian Islands in the US, where retail electricity prices routinely exceed 30¢ per kilowatt-hour, more than double some parts of the US, it would be impractical for interconnected OTEC to compete on cost. Previous OTEC initiatives have targeted Hawaii as a customer because the surrounding waters are ideal for OTEC and Hawaii gets the vast majority of its electricity from petroleum imported by sea [4].
In the maritime industry the cost per kilowatt-hour can be even higher [5] with larger environmental impacts due to the heavy fuel oils (HFOs) currently used [6]. Additionally, regulations have increased in this space and will continue to drive the market towards cleaner alternatives [7]. This has driven the prices of HFOs up and could create market conditions more suitable for alternative fuels, such as synthetic natural gas, ammonia, or hydrogen. These fuels could all be made using the output electricity of an OTEC plant.
Despite this apparent opportunity, most OTEC demonstrations have targeted onshore energy production that requires pumping cold water from far offshore or running long power cables back to the electric grid. There is no doubt that this will eventually be viable, but it is currently harder for OTEC to reach cost parity with terrestrial energy generation, due in part to a lack of investment. Others in academia and industry have cited a key problem blocking growth and further investment in this technology as the lack of a demonstration unit running at above 2.5 MW for more than a year [8]. It will take substantially larger OTEC operations, in the 100-400 MW range [3], to be cost competitive on the grid. However, smaller plants would be easier to build, operate, and move and could serve maritime customers who are already paying a premium for energy, to help increase investment and reduce the cost per kilowatt-hour.
This problem can be solved in a way that:
Drogue Energy plans to prototype and build offshore OTEC platforms that utilize the electricity generated for commercially viable ventures without exporting power back to shore. These platforms will be able to autonomously station-keep, move to avoid extreme weather, communicate with each other via mesh networking, harvest ocean thermal energy, and provide a platform for other companies that need sustained access to ocean resources or data.
At scale, this fleet of OTEC platforms could produce hydrogen or ammonia for shipping and agriculture, provide ground station access for growing satellite constellations, host carbon-negative edge data centers, or offshore test beds for other climate projects. There are endless viable commercial, industrial, and/or governmental partnerships for offshore platforms with unlimited baseload power. All of this can be achieved with proven technologies that are already in use today. If these industries are willing to initially pay a small premium for electricity (and real estate) at sea they could help accelerate the drive towards cost parity with other energy sources.
There are also a host of potentially beneficial climate side-effects from OTEC. The first is that certain types of OTEC naturally generate freshwater as a byproduct without the need for membranes or heating water like current desalination techniques. Residual cold seawater can also be used to cool industrial processes, servers in a data center, or air conditioning. The large volumes of cold water pumped from the deeper ocean can also benefit the marine ecosystem and sequester carbon through a process called artificial upwelling [9]. This process moves deep, nutrient-rich water to the surface, where it increases biological activity and leads to increased carbon uptake over time. All of these climate benefits would need further investigation, verification, and eventual attribution, but they seek to demonstrate the currently untapped potential of this technology.
To reduce costs and further the environmental benefits of building the first platforms, abandoned oil platforms and end-of-life commercial ships could be repurposed. Further testing could study the efficacy of mixing OTEC with other renewable energy sources, such as concentrated solar. This could result in a solution that: