There is currently an increasing interest in developing devices that can be used to exploit renewable energy in general and marine renewable energy in particular. Several sources of energy can be obtained from oceans, such as the energy produced by waves, tides, oceanic currents or thermal gradients, etc. It is important to stress that one of the most predictable sources of renewable energy is that derived from tidal and marine currents.
Several manufactures are developing devices with which to harness energy from ocean currents, and there is an extended trend towards the development of horizontal axis rotor turbines (HAT-TEC). There is, however, also a considerable amount of debate regarding both the use of fixed or controllable pitch rotors and the use of one or several rotors per device.
The decisions made in this respect have a great effect on the behaviour of the devices and the viability of the park as regards whether or not it will be technically and economically feasible. It is, therefore, necessary to be able to compare models and tools in order to design and choose the best and most feasible option. The tools most commonly used for metric comparison are: LCOE (Levelized Cost Of Energy), TRL (Technology Readiness Level) and TLP (Technology Performance Level).
This paper presents a formal procedure with which to compare various alternatives: On the one hand, previous results obtained by the GITERM-UPM Research Group as regards mono-rotor and multi-rotor fixed-pitch devices will be shown, together with their general characteristics. The possibilities of controlling them, which is achieved with the group’s own design of a ballast control system that is employed to carry out automatic emersion and immersion maneuvers to reduce the high economic cost of maintenance tasks and repairs, will also be explained.
On the other hand, the challenges involved in improving the design of the multi rotor will be listed, including the increase in the power of the rotor, the simplification of the structure, the improvement of the ability to control the device, etc. A new design for a multi-rotor device will also be presented, which takes advantage of the strengths of previous models and manages to substantially improve the amount of annual energy produced. This new device uses controllable pitch rotors, and its size and the amount of power produced by each generator have been improved.
Finally, an economic comparison is carried out by means of a series of cost-benefit indicators, and a formal procedure with which to compare their benefits through the use of LCOE is also proposed.