Integrating heterogeneous distributed energy resources to manage intermittent power at low cost

Abstract

A power distribution feeder where a heterogeneous set of distributed energy resources is deployed is examined by simulation. The resources include PV, battery storage, natural gas genset and fuel cells, and active thermal storage for commercial buildings. The resource scenario considered is one that may exist in a not too distant future, and is based on an existing demonstration system in Albuquerque, NM (USA). The operation of individual DERs, and its effects on the global power flow on the feeder, are considered. Two cases of interaction between different resources are examined. One interaction involves a genset used to partially offset the duty cycle of a smoothing battery connected to a large PV system. The other example involves the coordination of twenty thermal storage devices, each associated with a commercial building. The storage devices are intended to provide maximum benefit to the building, but it is shown that this can have a deleterious effect on the overall system, unless the action of the individual storage devices is coordinated -in which case there is overall benefit to the system. The main finding is that it is possible to achieve synergy between DERs on a system, however this required a unified strategy to coordinate the action of all devices in a decentralized way. I. BACKGROUNDRecent trends in small-scale distributed generation, particularly drastic price reductions of photovoltaic (PV) systems, will soon result in high penetration levels of variable generation, some of which is not directly controlled by a utility. Moreover, much of this generation is highly intermittent. As a result, concerns are growing on the ability of the utility to maintain uniform power quality over the length of a distribution feeder. Recent work has demonstrated that a battery energy storage system (BESS) can effectively perform two important tasks: shifting renewable power delivery to times of peak demand, and smoothing intermittent PV generation before it is injected into the feeder [1]. While this approach demonstrably works, batteries are still very expensive, and their lifetime is limited. In the present work, two examples are provided to show how distributed energy resources (DERs) other than batteries can be used to achieve similar or compleFig. 1. The Studio 14 distribution feeder in Albuquerque, NM, hosting a number of DER demonstration projects that could interact to maximize economic value and system performance.mentary goals at lower cost. One type of DER that is gaining increasing interest is the microgrid, in light of increased needs for both energy efficiency and high reliability. A microgrid is a collection of DERs that, from the viewpoint of the utility, is controllable, acts as a single load, and is able to function in both grid-tied and islanded mode [2]. An islanded micro-grid must have enough storage to compensate for any mismatch between load and generation while islanded. A second type of DER that is receiving renewed attention is thermal storage [3]. In the commercial and residential buildi...

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