# Distribution Integration

The goal of NREL's distribution integration research is to tackle the challenges facing the widespread integration of distributed energy resources while maintaining the safe, efficient, and cost-effective operation of the distribution system.

NREL's research on the integration of distributed energy resources began more than a decade ago and has included numerous high-impact projects. These projects have spanned the research spectrum from comprehensive projects in which we partnered with utilities to develop best practices for the integration of high levels of PV, to developing technical screening methods to “fast track” the interconnection of distributed energy resources, to evaluating the value of energy storage systems in the distribution system.

## Capabilities

- Modeling of advanced distribution systems, including quasi-static time-series models, planning-type models, distribution dynamic models, and advanced distribution system equipment models
- Modeling of microgrid systems
- Development of advanced distributed energy resources interconnection technical screens
- Modeling of aggregated distributed energy resource impact on the bulk system and verification with distribution-level phasor measurement unit data
- Evaluation of new distribution-level grid technologies
- Detailed analysis of distributed energy resource system costs, capabilities, and implemented use

## Projects

This project addresses the use of high penetrations of PV in islanded microgrids to increase overall system efficiency, decrease fuel costs, and maintain resiliency of the overall system. A real microgrid scenario with a high penetration of PV is being tested in NREL's Energy Systems Integration Facility. Multiple control cases for firming PV using storage tested.

In this project, NREL is providing research and testing support to San Diego Gas & Electric, including:

- Energy storage sizing and placement
- Integrated Test Facility development
- Real-time digital simulator modeling and simulation
- Visualization and virtual connection to NREL's Energy Systems Integration Facility
- Microgrid simulation and testing areas.

This project developed utility-relevant insights for the interconnection of high penetrations of distribution-connected PV systems. Efforts focused on:

- Developing distribution system modeling methods to determine the impact of high penetrations of distribution-connected PV on the local distribution system
- Making advances in how the variability of PV is modeled in quasi-static time-series simulations
- Performing field measurement-based validation of PV impacts on actual test circuits
- Laboratory testing of advanced PV inverter functionality
- Performing a field demonstration of advanced inverters' ability to mitigate PV-related impacts in high-penetration scenarios.

The capstone of the project was the development of an effective quick-start guide and reference for utility engineers working on distributed PV interconnection.

The Microgrid Cost Study is focused on identifying the costs of components, integration, and installation of existing U.S. microgrids and project cost improvements and technical accelerators over the next five years and beyond. This information can be used to develop research and development agendas for next-generation microgrids that provide cost-effective, reliable, and clean energy solutions. This project will provide insight, transparency, and standardization in the reporting of microgrid costs and identify market segment differences for future cost reductions across microgrid applications

Quasi-static time-series (QSTS) analysis of the distribution system is valuable when studying the anticipated impacts of interconnecting new PV systems. As the number of PV systems on distribution systems increases, the application of relatively simple, conservative assumptions or proxies for anticipated PV impacts becomes ever more unrealistic and potentially limits the amount of PV allowed to interconnect. However, the data and time required to complete QSTS analysis are formidable barriers to its everyday use in utility-relevant PV interconnection studies. This project seeks to eliminate these barriers by decreasing the time required to complete a yearlong 1-second-resolution QSTS study from 50 hours to 5 minutes and developing load and PV models that are easy to use with existing lower-resolution utility and environmental data.

## Publications

On the Path to SunShot: Emerging Issues and Challenges in Integrating Solar with the Distribution SystemPDF, NREL Technical Report (2016)

High-Penetration PV Integration Handbook for Distribution EngineersPDF, NREL Technical Report (2015)

In Divergence There is Strength: Measuring and Mitigating Solar PV Impacts in Southern
California Using Power Factors Other Than One, *IEEE Power and Energy Magazine* (2015)

Field Demonstration of Using Advanced PV Inverter Functionality To Mitigate the Impacts of High-Penetration PV Grid Integration on the Distribution System, IEEE Photovoltaic Specialist Conference (2015)