Environmental Engineering Reference
In-Depth Information
Wind Turbine System Performance
The principal measure of the performance of a wind turbine system is
annual energy out-
put
, which is the
electrical energy
delivered to the customer during a complete year [ASME
1989].
System power output
is often used as an intermediate measure of performance and is
deined by electrical power output as a function of steady wind speed (graphed as the
power-
versus-wind speed curve
or, simply, the
power curve
). Obviously, the net electrical energy
produced by a wind turbine system will depend on the energy of the wind passing through its
swept area, as well as on the eficiencies of its components.
A measure of the energy-conversion eficiency of a wind turbine system is its
coeficient
of energy
or
energy recovery factor
, deined as the ratio of its electrical energy output to its
wind energy input over the course of a year. Thus
ò
P
O
dt
C
E
=
AEO
G
E
W
=
year
(2-1)
ò
æ
ç
è
ò
p
W
dt
dA
year
A
where
C
E
= coeficient of energy or energy recovery factor
AEO
G
=
gross annual energy output (kWh/y)
E
W
= annual wind energy input (kWh/y)
P
O
= system output power (W)
t
= elapsed time (h)
A
= swept area of the turbine rotor; projection on a vertical plane (m
2
)
p
W
= wind power density (W/m
2
)
The term
gross annual energy output, AEO
G
, refers to the calculated electrical energy
delivered by a turbine to a speciied system output point in one year under the following
conditions:
--- Wind speeds and durations are equal to a speciied annual wind regime.
--- Wind speeds and durations are not affected by other turbines.
--- Turbine operates whenever wind speeds are in the speciied operating range
--- HAWT rotor axis is always aligned with the wind direction.
--- Turbine performance is not degraded by age, wear, dirt on blades,
etc.
--- Shutdowns for maintenance occur only when wind speeds are below the oper-
ating range.
Thus, gross annual energy output is a theoretical upper bound on the turbine energy
output.
It is often convenient during the design process to calculate the coeficient of energy on
the basis of a hypothetical
reference wind regime
that is representative of the wind speed
distributions in time and space expected to be present during operations. The principal fac-
tors involved in determining reference values of annual energy production and annual wind
energy will be introduced here and discussed in more detail in later chapters.
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