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Optimization Chapter | 9 245

C t
minimize (9.6)
E p
subject to constraints
where C t can be chosen as the total cost of the project, and E p is the total energy
production during the lifetime of the project. Alternatively, the investment cost
divided by AEP can be minimized, which does not take into account the interest
rate, operation and maintenance cost, and the time value of money.

Constraints
Micro-siting is subject to several constraints. The most common constraint is
the available area/plot for the farm (i.e. all turbines should be located inside the
array). The minimum distance between turbines can also be a constraint due
to technical issues or standards/regulations. Another constraint is the maximum
available investment. Although a large project can produce reasonable and lower
LCOE, the resources for financing a project are usually limited. The layout of a
wind farm may be subjected to some constraints to reduce the visual impact or
improve aesthetic design (e.g. Fig. 9.3B). Finally, forbidden areas in a farm can
limit the search space. These areas may be excluded due to foundation issues,
dedicated to electrical cable routes, etc.

Solution Techniques
Due to the complexity of the objective function and constraints of the wind
farm optimization problem, classical optimization techniques that are often
more suited to convex and continuous problems are less popular. Therefore,
metaheuristic methods are more effective and common in this area. Metaheuris-
tic approaches provide satisfactory solutions, but they do not necessarily find
the theoretical optimum. Genetic algorithm, particle swarm optimization, the
greedy algorithm, evolutionary algorithm, and ant colony are metaheuristic
approaches applied in this area [5,9].

9.2.2 TEC Array Optimization
Interdevice Spacing
The 2009 EMEC guide the assessment of tidal energy resources [10] recom-
mends that the lateral spacing between devices (the distance between axes)
should be two-and-a-half times the rotor diameter (2.5D), and the downstream
spacing should be 10D—both based on the assumption of horizontal axis
turbines. Further, the EMEC guide states that devices should be positioned in
an alternating downstream (i.e. staggered) arrangement (Fig. 9.5). Although
the exact details of device spacings is device-specific and can be debated (and
indeed no justification is given for the values 2.5D and 10D, although we can
assume that such guidance has propagated through from the wind industry),