Environmental Engineering Reference
In-Depth Information
the turbine hub height, correct for short-term climate variability, and extrapolate the
resource to turbine locations using numerical wind flow modeling.
Nevertheless, offshore environments offer unique challenges. These include a
scarcity of existing, high quality wind measurements taken at or near turbine hub
heights; the cost and delays involved in deploying measurement platforms offshore;
the need to account for the effects of currents, waves, and (in cold climates) ice in
the design of the platforms; the difficulty of reaching offshore sites for maintenance
and repair, especially in rough weather; heightened safety risks to field personnel;
equipment exposure to corrosive elements such as sea spray, salt water, and high
humidity; and extreme storm-driven winds and waves. These challenges mean that an
offshore measurement campaign usually costs much more than an onshore campaign
of similar scope.
This chapter focuses on the special considerations and requirements for offshore
resource assessment. It covers the nature of the offshore wind environment; the vari-
ety of monitoring station types and instrumentation, including remote sensing, that
can be used for resource assessment; ancillary systems such as power supplies, data
loggers, and communications; the challenges of offshore installation; and operations
and maintenance.
Aside from monitoring the wind resource, the design and permitting of offshore
wind projects requires characterizing other aspects of the ocean or lake environment,
including currents, waves, ice, and water temperature; the geophysical characteristics
of the seabed or lakebed; and fish, birds, and other wildlife. Although not a focus of
this chapter, the need to assess these parameters should be considered in concert with
the development of the wind resource assessment campaign, as they could affect the
siting, design, and operation of offshore monitoring stations. For example, platforms
might have to be larger to accommodate ocean- and wildlife-monitoring equipment,
they might need a more robust power supply as well as additional data logging and
communications equipment, and they might require a different schedule of operations
and maintenance visits. All these factors can increase capital and operations and
maintenance costs.
Finally, the decision of where to place an onshore monitoring station should take
into account the potential value of collecting data throughout the project's life cycle.
Placing the primary monitoring station within the planned array, as is usually done
for onshore projects to improve the accuracy of wind flow modeling, implies that any
wind resource data collected after the turbines become operational will be affected
by turbine wakes, making it difficult to obtain an accurate measure of the free-stream
speed. Siting the station upwind of the planned array, on the other hand, could yield
useful data for the ongoing analysis of the plant's performance, without substantially
reducing the accuracy of the preconstruction assessment because the wind resource
varies relatively little offshore. Given the costs, challenges, and time required to carry
out an offshore site assessment campaign, it is especially important to consider the full
scope of data needs for the project, both pre- and postconstruction, from the outset.
Coordinating and synthesizing the wind project's design, permitting, engineering, and
operational data needs will result in a comprehensive and high value monitoring
campaign.
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