Page 32 - Fundamentals of Ocean Renewable Energy Generating Electricity From The Sea

Introduction Chapter | 1 23

size of a wind turbine was 224 kW, but it was not until 2001 that turbines
exceeded the 1 MW milestone [20]. This transition was based on the concept of
establishing small-scale working generators, scaling up over time, and learning
from both successes and failures en route. In general, this path is being followed
for marine renewable energy devices, but there are important differences. First,
high wind speeds can occur in almost any region. These events could be rare in
some regions, and more frequent in others, but it is highly likely that at some
time in the lifetime of a wind turbine, an extreme ‘storm’ event will occur, that
the wind turbine must be designed to withstand. By contrast, fairly accurate
upper bounds can be placed on the extreme conditions that will be experienced
by either wave, and particularly tidal, energy convertors during their lifetime.
For example, because the tides are governed by astronomical tide generating
forces, we can predict with a high level of certainty the highest tidal currents
9
that will be experienced in a tidal channel over a 25-year period. Therefore,
robust (yet not overly engineered) tidal energy devices that are suitable for
economically exploiting this resource can be designed. Second, it is noticeable
that many device developers are working, at prototype and demonstration stages,
towards building fairly large precommercial turbines (e.g. the 1.2-MW SeaGen
device and the 2-MW OpenHydro device). This is understandable, because tidal
power is proportional to velocity cubed, and so there are high rewards from
successfully exploiting very high tidal streams. However, such scales of ocean
energy conversion could be considered to be fairly far along the analogous wind
turbine development timeline (Fig. 1.15), and so relatively high risk. Therefore,
it could be prudent to develop, in parallel, a range of devices suitable for
deployment in less challenging conditions, an example of which is the 100-
kW Nova Innovation M100 turbine. Such smaller devices, in addition to being
less challenging to deploy and operate, will have lower cut-in speeds, and so
are likely to achieve higher capacity factors when matched with an appropriate
resource (Section 1.5).

1.4.3 Roadmaps and Progress

Technology readiness level (TRL) is a system used to estimate technology
maturity, and is popular with NASA and the US Department of Defense, etc.
TRL is based on a scale from 1 to 9, with 9 being the most mature technology.
The use of TRLs enables consistent, uniform discussions of technical maturity
across different types of technology. Ocean Energy Europe 10 is a network of
ocean energy professionals with the common objective of creating a strong en-
vironment for the development of ocean energy. Within Ocean Energy Europe,

9. The expected lifetime of a marine energy device.
10. See https://www.oceanenergy-europe.eu/.