(240e) The Effect of Centralized Energy Storage on an Integrated Distributed Photovoltaics/CHP System for District Power, Heating and Cooling

The rise in availability of Distributed Energy Resources (DERs) has spurred utility companies and grid operators to search for methods to incorporate these resources (i.e., photovoltaics and energy storage) in the energy infrastructure in a manner that keeps the customers connected to the grid without jeopardizing grid stability and reliability. In the past decade, the explosive spread of photovoltaic generation (both rooftop and centralized) has lowered energy demand from conventional generation methods (i.e., power plants) during the afternoon. The result is the famous â??duck curveâ? for conventional electricity demand, with medium demand in the early morning, low demand in the afternoon (when the sun is shining), and a sharp increase to high demand in the evening when the sun sets ^[1]. While the growth trend for solar photovoltaic generation has important environmental benefits, it can â??if not properly managed â?? lead to an over-generation situation. In this case, demand during the day can be satisfied largely using solar power; however, the increased evening demand, corroborated with a natural drop in solar photovoltaic generation, may require very high power plant ramp rates. Most current power plants are unlikely to be able to withstand such rapid changes in generation rate. Motivated by this, significant research efforts have been expended towards defining strategies for controlling photovoltaic generation and grid-level storage systems. However, there are very few published works exploring the influence of photovoltaics and energy storage on the design of future power generation plants.

In our previous work ^[2], we provided a framework for simultaneous optimization of design and operation strategy for a CHP plant, providing the ability to select equipment sizes as well as plant operation modes to meet the projected electricity, heating, and cooling demand of a residential neighborhood. Based on realistic data collected from Pecan Street Research Inc., our results revealed that in the seasons with low electricity and cooling demand (winter and spring, considering a predominantly cooling climate), rooftop photovoltaic generation may exceed the neighborhood demand, while in the warmer seasons, the cooling capacity can often exceed the systemâ??s needs.

Motivated by the above, in this paper, we study the same system operating in an islanded (i.e., grid-disconnected) mode, and consider the impact of a centralized energy storage facility on system design and operations. We discuss an extension of our formulation for simultaneously optimizing the design and operation of the CHP plant and the centralized energy storage to minimize the capital and marginal costs of the CHP plant including transition penalties accrued by the equipment turning on and off. Using the aforementioned data collected from a neighborhood located in Austin, TX, we investigate the benefits of energy storage relative to the level of photovoltaic integration from the neighborhood, as well as identify economic benefits from photovoltaic integration and energy storage in terms of plant savings.

References:

^[1] CAISO (2016). What the duck curve tells us about managing a green grid. https://www.caiso.com/Documents/FlexibleResourcesHelpRenewables_FastFacts.pdf

^[2] Ondeck, A.D., Baldea, M., Edgar, T.F. Simultaneous Optimization of Design and Operation Strategies for CHP Systems. Computers & Chemical Engineering. Manuscript in preparation.