Page 233 - Wind Energy Handbook

REFERENCES 207

(r ¼ 0). This will pick out only the terms with k ¼ 1, for which r ¼ 1. If in addition
we divide the M uncertainty components into subsets of M A category A compo-
nents and M B category B components, Equation (4.17) simplifies to:
X X
M A
M B
2
2
2
u 2 ¼ c s 2 þ c u 2 ¼ s þ u 2 (4:19)
c,i k,i k,i k,i k,i i i
k¼1 l¼1
where s i and u i are the combined uncertainties for categories A and B respectively.
Varying the bin size from the standard value will affect the overall uncertainty
calculated. This is because s P,i depends on the number of data points in each bin,
according to Equation (4.17).
The combined uncertainty for annual energy production, u AEP , is given by:
! 2
N
N
X X X X
M A
M B
2
u 2 AEP ¼ N 2 h f 2 i c s 2 þ N 2 h f i c k,i u k,i (4:20)
k,i k,i
i¼1 k¼1 k¼1 i¼1
where f i is the annual wind-speed probability associated with bin i and N h is the
number of hours in the year. This expression differs from Equation (4.15), in that
the second term is an algebraic sum rather than a sum of squares which reflects the
fact that the category B uncertainty components are fully correlated across the
different bins.

References

Akins, R. E., (1978). ‘Performance evaluation of wind-energy conversion systems using the
method of bins - current status’. Internal Report SAND-77-1375. Sandia Laboratory,
Alberquerque, USA.
Christensen, C. J. and Dragt, J. B. (eds), (1986). ‘Accuracy of power-curve measurements’.
Riso-M-2632. Riso National Laboratory, Roskilde, Denmark.
Dragt, J. B., (1983). ‘On the systematic errors in the measurement of the aerodynamic
performance of a WECS by the method of bins’. ECN.
International Energy Agency, (1982). Recommended practices for wind-turbine testing and evalua-
tion: 1 Power performance testing. DTI, London, UK.
International Energy Agency, (1990). Recommended practices for wind-turbine testing and evalua-
tion: 1 Power performance testing, Second edition. (Currently available in third edition). DTI,
London, UK.
IEC, (1998). ‘Wind-turbine generator systems. Part 12: Wind-turbine power performance
testing’. IEC 61400-12.
ISO, (1995). ‘Guide to the expression of uncertainty in measurement’. ISO Information
Publication.
Pedersen, T. F. and Peterson, S. M., (1988). ‘Evaluation of power performance testing
procedures by means of measurements on a 90 kW wind turbine’. Proceedings of the EWEC.
H. S. Stephens, Bedford, UK.