PLANT DESIGN AND ENERGY PRODUCTION ESTIMATION - Wind Resource Assessment: A Practical Guide to Developing a Wind Project - page 240

type among small wind turbines designed mainly for residential or farm use, the power
can be estimated from the following equation:

P ρ site
ρ 0

P adj = (16.2)

where P is the turbine output for a given speed at the nominal air density. While
such adjustments are acceptable for making preliminary energy estimates, it is highly
recommended that the analyst obtain a certified power curve for a range of air densities
from the manufacturer before finalizing the project's energy production estimate.

16.5 DESIGNING AND OPTIMIZING A TURBINE LAYOUT

After choosing a turbine model, the resource analyst can begin to design the turbine
layout. This process usually involves balancing a number of competing goals.

• The first goal is the desire to make maximum use of the land under the devel-
oper's control. Up to a point, adding more turbines to a site increases the potential
production and, consequently, the revenues. When spread over the fixed capital
costs of the project (such as engineering studies, operations and maintenance
buildings, and the electrical substation and transmission line), the increased rev-
enues can result in a lower overall cost of energy, making the project more
competitive and profitable. Most developers, therefore, want to create as large a
project as possible.
• Second, there is the desire to maximize the capacity factor, or average output
as a fraction of the rated capacity. Assuming the same installation cost per unit
rated capacity, the higher the capacity factor, the greater the profit margin on the
project for a given power sales price. This goal usually works against the first,
as it implies making use of only the best wind resources in the project area and
placing the turbines far enough apart to keep wake losses small.
• The third goal is to minimize the plant installation cost. Aside from the turbines
themselves, two key elements of the installation cost are the access roads and
electrical collection system connecting the turbines together. By and large, the
shorter the required length of roads and cables, the lower the cost. In addition,
the steepness of terrain and barriers such as rivers and protected areas must
be considered. This goal usually argues for a relatively compact layout with no
“stranded” turbines (single turbines or small groups of turbines far from the rest).
• Last, the layout must satisfy the myriad regulatory requirements (such as set-
backs from property boundaries), environmental constraints (e.g., noise limits
at residences), community concerns (including visual and noise impacts), and
other issues that may constrain the placement of turbines. While some of these
constraints can be objectively met, others require subjective or qualitative judg-
ments.