Environmental Engineering Reference
In-Depth Information
Direct Value of Wind-Generated Energy to a Utility
The COE of a wind power station has meaning only when it is compared to the value
which the utility places on the electricity generated. Wind power can be evaluated on two
primary bases and on other secondary but possibly equally important values. Primarily wind
energy is a
fuel saver
and that it is a means of
deferring construction
of other types of power
plants or of transmission and distribution lines. When the wind is blowing, fossil-fueled or
hydroelectric plants can be turned down or off, thus saving their fuel or water.
Wind power plants can also have some
capacity value
, which will allow a utility to defer
the building of additional conventional plants. In addition, the
modularity
and
disbursed
generation
of wind turbines is a valuable asset in obtaining construction capital, because the
utility needs to install only the capacity required meeting near-term, not long-term, demand
and the wind plants can be located near load centers in areas where additional energy is
needed. The later is true if wind projects are developed by utilities rather than IPP's who
have no incentive for that site selection.
Fuel Savings
The value of wind-generated electricity based on the cost of fuel saved appears to be
relatively straight-forward, but utilities have some limitations on the amount of fuel that actu-
ally can be saved. As discussed in Chapter 4, the diesel-electric generators that power many
small utilities operate inefficiently at partial load, so there is a limit on how much their output
can be reduced without actually increasing their O&M costs more than the savings on fuel.
In a hydroelectric plant, the water “fuel” may have to be released anyway, in accordance
with agriculture, fish-maintenance and navigation requirements, even if power generation
requirements are offset by wind plants [EPRI 1993]. In all utilities, generating unit sizes and
requirements for
spinning reserve
also limit the rate and the amount by which conventional
generation can be turned down or off.
Capacity Value
A measure of capacity value used by utilities is the
load carrying capability
or LCC of
a power source. This is the power of an equivalent absolutely-reliable source (an ideal not
achieved by any real source) that would give the same contribution to the reliability of the
utility system during peak demand periods. If a utility were certain that a wind power plant
would be producing its full rated power during peak demand hours, than the LCC of this plant
would equal its power rating. At the other extreme, if a utility were certain that the wind
would never be in the operating range during peak hours, then the LCC of the wind power
plant would be zero.
In reality, the LCC of commercial wind power stations is somewhere between zero and
the station rating, depending on the specific “fit” of the wind power source to the utility's
seasonal and diurnal (daily) demand cycles. In the Pacific Gas and Electric (PG&E) service
area the greatest demand for electricity occurs during hot summer afternoons, when air con-
ditioner use and irrigation are at their highest rates. The output of the wind power stations
in the Altamont Pass is a good seasonal fit to this peak load, but their maximum daily output
occurs later than the maximum daily PG&E demand.
To obtain a rough approximation of the wind energy LCC for a specific location, the ac-
tual or projected wind power outputs during the hours of peak utility loads need to be studied
in detail. As an example, two wind power stations on sites in northern California were ex-
amined for their fit to the PG&E load cycle during a period of five years. These are an actual
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