Evaluation of Distribution Analysis Software for DER Applications

Abstract

The term ''Distributed energy resources'' or DER refers to a variety of compact, mostly self-contained power-generating technologies that can be combined with energy management and storage systems and used to improve the operation of the electricity distribution system, whether or not those technologies are connected to an electricity grid. Implementing DER can be as simple as installing a small electric generator to provide backup power at an electricity consumer's site. Or it can be a more complex system, highly integrated with the electricity grid and consisting of electricity generation, energy storage, and power management systems. DER devices provide opportunities for greater local control of electricity delivery and consumption. They also enable more efficient utilization of waste heat in combined cooling, heating and power (CHP) applications--boosting efficiency and lowering emissions. CHP systems can provide electricity, heat and hot water for industrial processes, space heating and cooling, refrigeration, and humidity control to improve indoor air quality. DER technologies are playing an increasingly important role in the nation's energy portfolio. They can be used to meet base load power, peaking power, backup power, remote power, power quality, as well as cooling and heating needs. DER systems, ranging in size and capacity from a few kilowatts up to 50 MW, can include a number of technologies (e.g., supply-side and demand-side) that can be located at or near the location where the energy is used. Information pertaining to DER technologies, application solutions, successful installations, etc., can be found at the U.S. Department of Energy's DER Internet site [1]. Market forces in the restructured electricity markets are making DER, both more common and more active in the distribution systems throughout the US [2]. If DER devices can be made even more competitive with central generation sources this trend will become unstoppable. In response, energy providers will be forced to both fully acknowledge the trend and plan for accommodating DER [3]. With bureaucratic barriers [4], lack of time/resources, tariffs, etc. still seen in certain regions of the country, changes still need to be made. Given continued technical advances in DER, the time is fast approaching when the industry, nation-wide, must not only accept DER freely but also provide or review in-depth technical assessments of how DER should be integrated into and managed throughout the distribution system. Characterization studies are needed to fully understand how both the utility system and DER devices themselves will respond to all reasonable events (e.g., grid disturbances, faults, rapid growth, diverse and multiple DER systems, large reactive loads). Some of this work has already begun as it relates to operation and control of DER [5] and microturbine performance characterization [6,7]. One of the most urgently needed tools that can provide these types of analyses is a distribution network analysis program in combination with models for various DER. Together, they can be used for (1) analyzing DER placement in distribution networks and (2) helping to ensure that adequate transmission reliability is maintained. Surveys of the market show products that represent a partial match to these needs; specifically, software that has been developed to plan electrical distribution systems and analyze reliability (in a near total absence of DER). The first part of this study (Sections 2 and 3 of the report) looks at a number of these software programs and provides both summary descriptions and comparisons. The second part of this study (Section 4 of the report) considers the suitability of these analysis tools for DER studies. It considers steady state modeling and assessment work performed by ORNL using one commercially available tool on feeder data provided by a southern utility. Appendix A provides a technical report on the results of this modeling effort.