In the global quest for clean energy, the ocean continues to be recognized as a vast “blue treasure trove” of potential. Where warm surface waters meet deep cold currents, a quiet transformation of energy across a temperature difference of 20°C is possible—this is the principle behind Ocean Thermal Energy Conversion (OTEC). Recently, China’s independently developed 20-kilowatt floating OTEC device completed its first sea trial in the South China Sea, successfully igniting a crucial step in transitioning this technology from the laboratory to practical engineering application.
OTEC: The ‘Solar Battery’ Hidden in Seawater
At its core, OTEC utilizes the temperature difference between warm surface seawater (approximately 25-30°C) and cold deep seawater (approximately 4-7°C) to drive a thermodynamic cycle. The principle is similar to traditional thermal power plants: heat from the warm seawater is transferred via a heat exchanger to a low-boiling-point working fluid (such as ammonia or a refrigerant), causing it to evaporate into high-pressure vapor that drives a turbine generator. Subsequently, cold seawater condenses the vapor back into liquid, completing the cycle. This process requires no fossil fuel combustion, produces zero carbon emissions, and the equipment can operate stably 24/7, unaffected by waves, wind, or other variable natural conditions.
Scientists note that OTEC potential is most abundant in tropical ocean regions. Taking the South China Sea as an example, surface water temperatures remain above 28°C year-round, while at 1000 meters depth, the temperature is only 4-6°C, creating a vertical temperature difference exceeding 20°C. Global estimates suggest the annual energy potential of OTEC ranges from 30,000 to 90,000 TWh, potentially several times the world’s current annual electricity generation. The theoretical OTEC capacity in the South China Sea alone exceeds 3,000 MW, enough to power a city of one million people.
From Lab to Deep Sea: Breakthroughs in Chinese Technology
Although the concept of OTEC was first proposed as early as 1881, its practical implementation has faced three major challenges: efficiently drawing cold deep water, reducing equipment costs, and improving energy conversion efficiency. After a decade of dedicated research, a Chinese scientific team achieved a breakthrough in August 2023. A 20-kilowatt floating power generation device, deployed from the research vessel “Marine Geology No. 2,” successfully completed its inaugural sea trial in waters 1900 meters deep in the South China Sea.
According to the latest news, the heart of this device is an independently developed, small-temperature-difference, wide-load turbo-generator that can stably output electricity with just a 20°C gradient. Its “veins” are deep-sea insulated cold water pipes, which use special materials to bring cold water to the surface with minimal heat loss. The “brain” is an intelligent control system that monitors parameters like warm water flow and working fluid pressure in real-time to ensure efficient operation. Trial data showed the device achieved a maximum power output of 16.4 kW and a net conversion efficiency of 17.7%, marking China’s entry into the small group of countries mastering core OTEC technology.
The Future Landscape of Blue Energy
The potential of OTEC extends far beyond electricity generation. Nutrient-rich deep seawater, brought to the surface, can promote the growth of marine plankton, providing natural feed for aquaculture. The cold water can also be used for air conditioning cooling, seawater desalination, and even the production of high-value-added products (such as deep-sea mineral health supplements). For instance, a hypothetical 100 MW OTEC plant could desalinate approximately 378 cubic meters of seawater daily while producing significant amounts of nutrient-rich water, creating a circular economic model integrating “power generation-aquaculture-desalination.”
Currently, several experimental OTEC plants exist worldwide, but commercial application still faces cost hurdles. Chinese research teams are working to reduce costs by optimizing materials, simplifying structures, and enhancing efficiency. Examples include using domestically produced high-performance titanium alloy heat exchangers to extend equipment lifespan beyond 30 years and developing modular designs for easier offshore assembly and maintenance. With ongoing technological iterations, the future cost of OTEC-generated electricity is projected to potentially fall below $0.04 per kWh, complementing other renewable sources like offshore wind and solar power.
At the crossroads of the global energy transition, Ocean Thermal Energy Conversion opens a window to a more sustainable future. As the waves of the South China Sea lap against this pioneering device, this green revolution, driven by temperature differences, is subtly reshaping the relationship between humanity and the ocean—transforming us from mere extractors into guardians, from energy consumers into clean energy producers. Perhaps in the near future, the lights of our cities, the machinery of our industries, and our offshore platforms will all be powered by the blue energy rising from the deep sea.
