Energy Output


Innovation Norway has funded a theoretical analysis of the Subwave turbin. The analysis was conducted by Dr. Karl Christian Strømsem, Global Maritime AS, and presented in a report in September 2014. The analysis was based on the expected capacity of the turbine to convert wave energy from a coastal wave climate outside Karmøy on the west coast of southern Norway.

In the summary, Strømsem writes:

Analysis of the proposed system show that it will be necessary to increase the blade lengths substantially in order to achieve a reasonable energy capture with the device. An example show that increasing the blade length from 1 meter to 7.5 meter increases the energy capture from 2.5 % to 21.7 % of the incoming energy. Analysis using a typical near shore wave climate (Karmoy scatter diagram) gives a yearly production in the range of 150 MWh for a turbine with 5 meter long blades. The torpedo with the two turbine blade rings, counter acting generator kept away from the active wave zone is an interesting solution and addresses issues related to extreme loads and wave energy conversion without direct contact with the waves in an elegant way. A nice feature of the system is that it is easy to retrieve and maintain by simply disconnect and bring to shore.

This table summarizes the energy yield in relation to the wing length and buoy size.

In addition, Strømsem has assessed the value of the energy in the Norwegian and British pricing regime (2014).

In closing comments Strømsem writes:

  • We have concluded that it is necessary to increase the diameter the turbine blades span. The energy production is a function of swept area and hence a power of 2 of the length of the blades. The longer the blades the more energy is produced (up to a limit).
  • We believe that the energy production numbers derived from this analysis are relatively realistic.
  • Using the 30 % generator/conversion efficiency we see that the system should be able to capture around 22% of the incoming wave energy. This is in line with what can be considered industry practice.

Link to the report here (653 kB, pdf).