Introduction

The concept we are proposing in this project arises as an innovation in the field of offshore renewable energy. We are combining two forms of energy generation into one device, with the aim of creating a feasible technology. The use of a hybrid device has advantages and drawbacks that will be explained in the different sections of this website.

It could be said that our proposal follows the rule 'the simpler, the better': we have taken an offshore wind turbine, supported by a monopile, and we have added two tidal turbines to the submerged part of the structure. The addition of this two turbines is done by wielding the tidal supporting structure to the transition piece, which is the piece that joins the monopile and the wind turbine tower. The tidal turbines and the wind tower will be added to this piece later, as explained in the operation and maintenance part.

The addition of the tidal turbines implies extra loads to the supporting pile. The effect of these extra loads has been studied in the structural analysis.

Transition piece
Figure 1: Transition piece modified for the hybrid device

Tidal and wind turbines

The device
Figure 2: HOWaT system

Two different turbine models have been chosen for wind and tidal generation. The wind turbine is NREL 5 MW, whilst the tidal turbine is Atlantis' SeaGen-S 2 MW. The following table shows some details about the general characteristics of the hybrid device:

Characteristic of the hybrid device
Wind rated power 5 MW
Tidal rated power 2 MW
Wind rotor diameter 120 m
Tidal rotor diameter 20 m
Wind turbine height 87 m
Tidal turbine depth 14 m

There is more information about the characteristics of the HOWaT system in the pages concerning the wind and the tidal concepts.

Advantages and disadvantages of HOWaT

The system we are proposing has some advantages and drawbacks with respect to a wind offshore or a tidal generator. Before doing any deeper research, these are some of them:

Advantages

✔ Tidal resource is predictable
✔ Energy density is increased
✔ Costs are reduced through shared transmission and supporting structures
✔ Maintenance costs are shared

Drawbacks

✘ Tidal energy is still an immature technology
✘ Structural loads are increased
✘ Increased vibration on the structure
✘ It is difficult to find appropriate locations

In this project we have tried to check if such a device can be actually used, and if it is financially viable. We have discovered some interesting conclusions, which will be explained in their corresponding pages.