Optimal Policies for Simultaneous Energy Consumption and Ancillary Service Provision for Flexible Loads under Stochastic Prices and No Capacity Reservation Constraint

摘要

Flexible loads, i.e. the loads whose power trajectory is not bound to aspecific one, constitute a sizable portion of current and future electricdemand. This flexibility can be used to improve the performance of the grid,should the right incentives be in place. In this paper, we consider the optimal decision making problem faced by aflexible load, demanding a certain amount of energy over its availabilityperiod, subject to rate constraints. The load is also capable of providingAncillary Services (AS) by decreasing or increasing its consumption in responseto signals from the Independent System Operator. Under arbitrarily distributedand correlated Markovian energy and AS prices, we obtain the optimal policy forminimizing expected total cost, which includes cost of energy and benefits fromAS provision, assuming no capacity reservation requirement for AS provision. Wealso prove that the optimal policy has a multi-threshold form and can becomputed, stored and operated efficiently. We further study the effectivenessof our proposed optimal policy and its impact on the grid. We show that, while optimal simultaneous consumption and AS provision underreal-time stochastic prices is achievable with acceptable computational burden,the impact of adopting such real-time pricing schemes on the network might notbe as good as suggested by the majority of the existing literature. In fact, weshow that such price responsive loads are likely to induce peak-to-averageratios much more than what is observed in the current distribution networks andadversely affect the grid.