Distributed Energy Resources Operations in the Modern Grid

By Michael Emmanuel, Ramesh Rayudu, Ian Welch

The modern grid is expected to have the capacity to adequately host and integrate all types and sizes of electric power generation sources and storage systems in a plug-and-play fashion. Leveraging on robust deployments of distributed energy resources (DERs) such as solar photovoltaic and wind systems as modern grid solutions has become a major component of smart grid initiatives.

The imminent modernization of the power grid provides all stakeholders with both opportunities and challenges, including authorities having jurisdiction over the grid (AHJs), utilities and prosumers. The modern grid is geared towards the decarbonisation of the energy production, the electricity market deregulation, and a more reliable and secure operation of the evolving, complex and dynamic electric infrastructure. Also, certain critical performance metrics are expected to help assess the effectiveness and efficiency of the operation of the grid. These metrics include the penetration levels of distributed energy resources (DERs), power losses, emissions per kilowatt-hour (kWh) delivered, the cost of interruptions and power quality issues.

Successfully harnessing the capabilities of DERs and storage systems represents a major milestone in the modernization of the conventional electric grid. Provided the feeder hosting capacity is not violated at any point, the benefits of DER include incremental capacity additions, power delivery system relief, power loss reduction and voltage support. However, since the traditional electric power system (EPS) was not designed for bidirectional power flows, the proliferation of DER on the network poses a great threat to the reliable and safe operation of the grid. Some of the risks include excessive operation of voltage regulating devices, reverse power flow during minimal load conditions and conflicting control objectives between the network and DER. Apart from these technical challenges, the utility is also faced with the economic challenge of reduced kWh sales. Therefore, in order to leverage DERs as an emerging smart grid solution, existing regulatory policies have to be modified in order to incentivize utilities for providing the needed platform and flexibility for grid modernization (e.g., by providing cost recovery for investment). Another critical factor for rapid and successful DER technologies uptake are policies which ensure maintenance of power quality within specified limits and equity in cost allocation as a result of interconnection.

The ever increasing penetration of DERs such as solar photovoltaic and wind generations in the distribution network requires global research collaboration and practical case studies capturing the experience of utilities deploying DERs in the evolving power grid. This will help the development of adequate grid codes and standards for “best practices” and the effective management of the proliferation of DERs in the active distribution network. For instance, the IEEE 1547-2003 standard suite intended for passive and low DER penetrations is evolving rapidly. The IEEE 1547a-2014 now stipulates that, with the permission of the local EPS operator, DER shall actively participate in voltage regulation through proper control of their of active and reactive power output. There is also a complementary standard, IEEE 1547.8, which ensures more flexibility in ascertaining the design and processes used in expanding the deployment methods used for DER integration with the EPS. Therefore, a collaborative effort is needed to update existing technical documents which would ensure that the value attributes provided by DER are maximized, that there exists a full characterization of their operation with respect to the existing infrastructure, and that the operational challenges imposed on the grid are properly handled.

Further, the modern grid is expected to seamlessly host different types and sizes of DER and storage systems in a “plug-and-play” fashion with device interchangeability and interoperability support. However, the legacy power grid is a monolithic system with proprietary devices making interoperability a major issue. Therefore, as previously stated there is a critical need to improve the DER integration standards and codes to allow different power generation technologies to be seamlessly integrated with the EPS while retaining the grid reliability, performance and safety.

Another requirement for widespread adoption of DERs is a DER management system (DERMS). Prototypes are being developed by various research laboratories to control, organize and manage DER operations in the modern distribution grid. The deployment of DERMS enables the distribution management system (DMS) to receive the near real-time status, dispatch schedules, production values and optimization of aggregated DERs in the grid. Also, an integrated DERMS has the capacity to improve the operational reliability of the modern grid by enabling the DMS to have predictive control, operations and management of the complete life cycle of utility-interactive DERs. Recently, the Electric Power Research Institute, Sandia National Laboratories, National Renewable Energy Laboratory and the U.S. Department of Energy have engaged into a rigorous research program to develop international standards for communication interfaces for DERMS and inverters. With the current high penetrations of DERs in the electric grid, it is now apparent that the DERMS application is a critical component in the next-generation grid if the operational reliability and power quality within regulatory-prescribed limits are to be maintained.

However, successful deployment of DERMS application would depend on reliable, standard and widespread communication network technologies for DER dispatch, control and coordination. As an example, for DER critical control and intended islanding, a communication technology (such as Fiber-optic and Worldwide interoperability for Microwave Access) with exceptionally short latency, extreme high data rates and availability is required. In general, IEEE Std 1547.3 -2007 recommends four critical performance metrics for assessing and characterizing communication network technologies performances for DER interconnection with the EPS. These metrics are throughput, latency, reliability and security.

A well-managed, robust deployment of DER technologies is a key element in the modernization of the electric grid with far reaching benefits for all stakeholders such as the Government, utilities, AHJs and prosumers without compromising reliability, safety and protection in a cost-effective manner. As DER interconnection request continues to increase, underpinned by various incentives, improved modelling tools and methods are required to support accurate characterization of feeder operations and effective mitigation alternatives to handle adverse impacts on the reliable operations of the modern grid. Also, a thorough revision and deeper understanding of DER interconnection standards, procedures and grid codes for best and safe practices are critical for a successful adoption of DER as modern grid technologies.

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