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equirements, manufacturers of variable-speed wind
turbines are implementing solutions to reduce the sensitivity
of variable-speed wind turbines to grid voltage drops.
The impact of wind power on reactive power generation
and voltage control originates first from the fact that not all
wind turbines are capable of varying their reactive power
out-put. However, two other things have to be considered.
First, wind power cannot be very flexibly located when
compared to conventional generation, so the voltage control
aspect can not be as easily considered as in case of
conventional generation. Second, wind turbines are
relatively weakly coupled to the system because their output
voltage is rather low and because they are often erected at
distant locations, which further reduces their contribution
towards voltage control.
Wind power hardly ever contributes to primary
frequency regulation, due to intermittent nature of the prime
mover. Further, the variability of the wind on the longer
term (15 minutes to hours) tends to complicate the load
following with the conventional units that remain in the
system, as the demand curve to be matched by these units
(which equals the system load minus the wind power
generation) is far less smooth than would be the case
without wind power. This heavily affects the dispatch of the
conventional generators. The impact of wind power on
frequency control and load following becomes more severe
the higher the wind power penetration level is.
In order to find the best control and operating strategies
that will power system stability, detailed analysis with
simulation models for every specific system should be
carried out.
III. ECONOMIC CHARACTERISTICS OF WIND ENERGY USE
Economics of wind power projects (WPP) should be
evaluated in the same way as any other investment.
Economic analyses of investment projects are based on the
progress of future cash flows during the lifetime of the
project and evaluation of project cost effectiveness using
various profitability indicators, like payback period, net
present value and/or internal rate of return.
The main parameters governing wind power project
economics include the following [6]:
Investment costs;
Operation and Maintenance (O&M) costs;
Electricity production/average wind speed;
Turbine lifetime (lifetime of the project);
Discount rate.
First two items denote the most important WPP
expenditures, while the third denotes WPP revenues.
A. Wind Power Project Expenditures
The largest share in WPP costs are attributed to the
investment or initial costs. They most usually include costs
for preparing a feasibility study (preparation works at the
micro-location like measurement of wind velocity and
direction, geological assessment, etc.), performing the
project development functions (power purchase agreement,
permits and approvals, land rights issues, etc.), completing
the necessary engineering (electrical, mechanical and civil
design, tendering documentation and contracting),
purchasing and installing the energy equipment, the balance
of plant (wind turbine(s) foundations(s) and erection, road
construction, transmission line, additional substations,
transportation costs) and costs for any other miscellaneous
items. The energy equipment and balance of plant are the
two cost categories showing the strongest dependence on
the number of wind turbines that make up the wind farm.
Hence, the larger the wind farm, the more relative weight
these two categories represent. Table I suggests typical
ranges of relative costs.
TABLE I
RELATIVE INVESTMENT (INITIAL) COSTS OF WIND POWER PLANT [7]
Cost category Large Wind Farm Small Wind Farm
(%)
(%)
Feasibility Study