A problem with managing the electric grid is the variability of wind-generated electricity, particularly when it represents a significant fraction of the total electric power. One solution for smoothing the variability in wind production is energy storage. Unlike conventional thinking of using electric energy storage, this paper discusses the opportunity to use ice-storage for air conditioning in large commercial buildings to provide the smoothing (i.e., balancing) services. When the wind generation is high so that excess electricity is available, ice is made. When wind generation ceases and the grid demand exceeds generation capacity, the air conditioning supplied by chillers is shut down and cooling is provided by the stored ice.
Exploring thermal energy storage for the wind balancing was motivated by the observation that thermal energy storage using ice is an order of magnitude less expensive than electric energy storage. This paper addresses the technical challenges and economic opportunities of operating a chiller/storage system to balance the wind production for the grid and well as meeting the building cooling needs. If ice storage is to be an effective approach for wind balancing then the system must be optimized in a way that ensures that both the commercial building owner and the electric distribution system profit.
The paper describes the features of a combined ice storage/chiller system operation and details the numerical approach to achieve an optimal strategy that minimizes operating costs. Because of the high variability of wind electricity generation, the time discretization of the optimization had to be of the order of 5 minutes which increaes the size of the optimization problem significantly. The optimization problem is non-linear when a real time pricing rate structure to the commercial building owner is considered. This paper discusses the results of exploring the optimal control strategies under various conditions.
