Estimating the Spinning Reserve Requirements in Systems With Signiﬁcant Wind Power Generation Penetration
Spinning reserve (SR) allows system operators to compensate for unpredictable imbalances between load and generation caused by sudden outages of generating units, errors in load forecasting or unexpected deviations by generating units from their production schedules. As the proportion of power produced by wind farms increases, it becomes more difﬁcult to predict accurately the total amount of power injected by all generators into the power system. This added uncertainty must be taken into account when setting the requirement for SR. This paper proposes a technique to calculate the optimal amount of SR that the system operator should provide to be able to respond not only to generation outages but also to errors in the forecasts for load and wind power production. Using a Monte Carlo simulation, the proposed technique for setting the SR requirements is then compared with the traditional deterministic criterion (i.e., the capacity of the largest online infeed), an approach to cope with wind imbalances and an approach that combines the traditional criterion with the approach to cope with wind imbalances. The results show that, contrary to what is commonly believed, an increased wind power penetration does not necessarily require larger amounts of SR.
WIND power generation is a major renewable resource used in many countries to replace conventional generation and reduce greenhouse gas emissions. However because wind generation can only be controlled by “spilling wind” and because its power output cannot be predicted with great accuracy, a substantial increase in the proportion of power produced from wind has a signiﬁcant impact on the way in which scheduling and dispatch are performed. If wind power generation is viewed as a negative load, the uncertainty on this generation increases the uncertainty on the net demand (i.e., the system wide demand minus the wind power generation) that must be met by traditional forms of generation. This increased uncertainty must be taken into account when determining the requirements for spinning reserve (SR) because this reserve is intended to protect the system against unforeseen events such as generation outages, sudden load changes or a combination of both. One might therefore expect that a large penetration of wind generation might require a signiﬁcant increase in the requirement for SR. However this is not always the case. The cost of SR is indeed far from negligible. If larger amounts of SR must be scheduled because of a higher wind-power penetration, then a larger number of conventional generating units will need to be synchronized. This would increase the system operating cost to such an extent that it might be economically desirable to curb this increase in the SR requirement. Determining the optimal amount of SR that must be provided as a function of the system conditions is thus an important and timely issue. The optimal amount of SR is such that the cost of providing an extra MW of reserve is equal to the beneﬁt that this MW provides, where this beneﬁt is measured in terms of the reduction in the expected cost of interruptions. Ideally the energy and SR amounts and repartitions should be optimized simultaneously. The main difﬁculties in solving such a problem are: the stochastic nature of the net demand due to the demand and wind forecast errors, and the fact that there are no direct means of incorporating the discrete capacity outage probability distribution in the optimization procedure. The stochastic and highly combinatorial nature of the problem led some researchers to ﬁnd alternative solutions to the problem
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