Earth Notes: Eco Puzzler: Ocean Heat MW

Updated 2024-02-20.
For those on their way to mastering engineering... How to generate 200MW electricity from ocean thermal differences? #ecoEngineering #renewables
From a series of eco puzzles set for real MEng students by "The Prof". This one is about the nascent technology of energy from thermal differences in a marine environment which could potentially be a useful addition to a portfolio of renewable energy sources.

Text lightly edited from real project work description for MEng students.

Many thanks to "The Prof" for so generously making this material available!

Ocean Thermal Electricity Generation

By: ""


You will be aware of the moves to increase the amount of energy generated from renewable sources. You will also be aware that this is not straightforward. There is plenty of renewable energy about but its density in the environment is low and so collecting it means a widespread and, therefore, expensive infrastructure. Also, it is difficult to match availability to demand in a simple way; solar energy comes when the sun shines, wind and waves (forms of solar) when the wind blows, tidal according to the moon, and so on. Hence, in thinking about a system for renewable energy for a community, it is important to link in as many diverse sources as possible.

This puzzler is about the nascent technology of energy from thermal differences in a marine environment which could potentially be a useful addition to a portfolio of renewable energy sources. Certainly, it does not necessarily depend on short cycles of weather and rotations of the earth and moon. More likely, and unusually for a renewable source, it probably has the potential to be a steady-state, base-load power generator.

The project

The projects are to carry out the concept/feasibility designs of two variants of a Thermal Difference Power Station. Each will have a target maximum output of 100 MW as electrical energy which should be available at all times. One power station is to run on the difference in temperature between surface of the ocean and the temperature at depth; the other is to run on the temperature difference between the ocean surface and ambient air temperature.

You will have to choose the best location for your particular plant, each of which is most likely to be an enormous heat-engine of some configuration (it might just possibly be an enormous thermopile). The mass flow rates will be huge and it is most probable that the internal power consumption to run the plant will exceed the net output. Hence system efficiency will become extremely important. To help with the overall efficiency, you will be encouraged to look for economic uses of spent discharges from the plants.

Amongst other things, you will need to consider:

  1. siting, including closeness to a grid node and/or consumer community
  2. which technology to exploit
  3. the actual design of the plant
  4. any necessary features to control marine fouling
  5. secondary economic uses of spent discharges, such as food production, fresh water and “coolth” for buildings
  6. environmental impacts
  7. how to eliminate or at least, mitigate, the risks from innovation, the weather, the site conditions and so on.


The economic viability is to be expressed in terms of Energy Return on Energy Invested (EROI).

To calculate this you will need to estimate energy used in construction and decommissioning and the net energy generated over, say, a 30 year operating life. Including the secondary uses, if employed, will make this a very interesting calculation.

Skills needed

These plants will be large installations built on-shore, off-shore on fixed structures, floating off-shore or on the sea bed. They will need to collect and process huge volumes of fluids. Hence, on the face of it, the principal disciplines appear to be chemical engineering, civil engineering and mechanical engineering. However, these plants are operational prototypes based nascent technologies and so our limiting skills to these conventional three may rule out interesting solutions.

(Level: Masters; group work, learning activity.)