Tidal Current Energy

144 R. Alcorn and T. Lewis
9.1.1 .
Resource
This is annualized energy availability at the chosen site. It will normally be summarized
in kW� m � 1 , but ideally should be given as a spectrum so that the device
performance can be matched against it. A high value of wave resource normally
means that the design wave is also high. For example, on the west coast of Ireland,
the resource may be 60 kW�m � 1 but the 50-year design wave is up to 32 m.
9.1.2 . Device performance – efficiency and tunability
This is how the device responds to the energy resource at the given site. The
tunability of a device should allow standard devices to tune to slightly different
wave resources. The combination of resource and efficiency, along with an
understanding of when the unit sheds power along with its expected availability,
allows the calculation of annualized energy output per device in GW�h.
9.1.3 . Capital cost
This is the total capital cost for a commissioned device or farm which is capable
of producing saleable power at the point of connection. The capital costs are
detailed further in the next section.
9.1.4 . O & M costs
These are the ongoing operational costs of the device. The method and frequency
of maintaining a device and its accessibility will greatly affect these
costs. For example, a sub-sea unit may require divers and specialized vessels
but may require less frequent attention.
9.1.5 . Design life
The capital costs, O & M costs and decommissioning costs will be amortized
over the design life of a unit. Currently within the industry, design life targets
are conservative, at around 10–15 years. Most business plans also factor in at
least one major refurbishment throughout the design life. They also factor in
the decommissioning costs at the end of the useful production life. Surprisingly,
design life is not usually limited by extreme events, but instead by structural
and component fatigue life due to the continual reciprocating load cycles.
9.1.6 . Price of energy unit
This is the power purchase price or the price that a unit of electricity can be sold
for. This will vary depending on a number of factors, including incentives, tariffs,
carbon credits and whether the power output is dispatchable.
Taking these points into consideration it can be seen where the focus of development
is at the moment. The lowest hanging fruit from a project perspective
would be a high resource close to a market where the energy price is high.
Ideally, the project would be near to a port to facilitate O & M, as well as reduce
the length and hence cost of both vessel transits and cable interconnection.
Although the business model of wave energy developers contains these elements
at the very least, the income stream differs greatly between them. Some