Thermal Energy Storage, Solar Energy, Wind Energy, Peak Load Reduction, Commercial Buildings
Recent international agreements on climate change aim to increase the production of electricity derived from renewable energy resources.Â Renewable energy generation can be pursued on both an individual building and utility scale. Due to the intermittent nature of renewables, some form of energy storage is essential to bridge diurnal mismatches between generation and demand.Â Air-conditioning loads associated with commercial buildings dominate peak electricity demand on the utility grid in some areas and climates.Â Therefore, Cool Thermal Energy Storage (CTES) is a relatively technically mature and inexpensive means of providing this â€œstorageâ€ and balancing supply/demand mismatches, thereby enabling the success of increased renewable energy penetration.Â Electrical energy generated by renewables during periods of higher availability can be used to run chillers that charge CTES systems.Â The stored thermal energy can subsequently be used to meet air-conditioning demand during periods of low renewable energy resource availability. Â In this work, the U.S. Department of Energy Commercial Reference Building Model for a secondary school is used to obtain simulated cooling loads that are met by a combination of two chillers and a stratified chilled water thermal storage system. Control strategies are designed to charge the thermal storage system when renewable resources are available and discharge storage to meet building cooling loads during periods with low or no renewable energy resource. One optimization target is the fraction of the chiller energy consumption met by renewable power. This metric is one that may be of interest to electric utilities trying to manage a grid with increasing renewable penetration.Â An alternative optimization target is the net economic benefit to the building owner assuming on-site, small scale renewable generation and thermal storage.Â This metric is based on equipment costs, net electric demand after wind and/or solar generation offsets the chiller electric demand, and time-of-use electricity rate structures. Â The results show that there is a trade-off between maximizing the use of renewable power and life-cycle cost, but a storage system designed to optimize either variable will be more cost effective and utilize the renewable resource better than a system without storage. The analysis is carried out for locations in Texas and California.Â These results suggest that CTES may be a technology enabling utilities to reach higher penetration of renewables while avoiding the so-called â€œduck curveâ€ generation ramp caused by the time mismatch between the renewable generation and demand peaks.