Reactive power management is key to improving grid stability – pv magazine USA

July 29, 2024 IEA-PVPS

From pv magazine Global

As the global energy landscape shifts towards renewable energy sources, effective reactive power management becomes critical to ensuring grid stability and reliability. The recent IEA PVPS Task 14 report, “Reactive Power Management with Distributed Energy Resources,” delves into state-of-the-art practices, best practices, and recommendations for reactive power management in the face of the growing integration of distributed energy resources (DERs). This paper provides a comprehensive review of the report’s findings, regulatory frameworks, and practical applications, emphasizing the critical role of reactive power management in maintaining a stable and efficient power grid.

The importance of reactive power management

Reactive power management is essential for maintaining voltage control, ensuring high power quality and increasing overall grid stability. It helps prevent issues such as harmonics, flicker, unbalanced loads and power oscillations that can negatively impact power quality and the ability to efficiently transmit power. With the increasing integration of DERs such as photovoltaic (PV) systems, these assets must assume greater responsibility for providing reactive power control. This improvement in power system stability is critical for preventing issues such as load shedding and system collapse, ultimately increasing the safety and reliability of the power system.

Goals and Purpose of the Report

The IEA PVPS Task 14 report aims to provide a summary of state-of-the-art management practices, best practices and recommendations for reactive power management. It analyses the regulatory frameworks in selected countries, highlighting different approaches to reactive power management. The report offers insight into the current status and future prospects of reactive power management in the context of increasing DER integration and examines the effectiveness of different regulatory frameworks in supporting reactive power management.

Regulatory requirements and practices

The report covers regulatory requirements in selected Task 14 countries and research and application examples from these countries. It provides an overview of reactive power regulations in different countries, detailing the grid codes and frameworks that shape the requirements for connected DERs to provide reactive power control. Task 14, for example, examines how these regulations affect the operation of energy systems with increasing integration of renewable energy sources. Germany will be mentioned as an example of regulatory requirements in this article.

Example: German Grid Codes for Reactive Power Assurance DER

In Germany, the current grid codes require that DERs provide controlled reactive power during energization. The guidelines ensure that DERs effectively contribute to grid stability by providing the necessary reactive power. This capability allows distribution system operators (DSOs) to use DERs for additional system services. The requirements vary depending on the voltage level:

• Low voltage (LV):The VDE-AR-N 4105 standard specifies that DERs with a capacity of ≤4.6 kVA must provide reactive power at a minimum power factor of 0.95, while larger DERs should provide a minimum power factor of 0.9.
• Medium voltage (MV):The VDE-AR-N 4110 standard requires that DER maintain reactive power within a specified range when the active power fed into the grid exceeds 20% of the installed capacity, ensuring stability at the point of connection (PCC).
• High Voltage (HV): VDE-AR-N 4120 offers three options for providing reactive power based on the active power of the generator and its capacity. Each version specifies different over-excited and under-excited power factors, allowing OSDs to select the most appropriate option for their specific needs. OSDs can select one of the suggested options based on the specific circumstances in the PCC of each generator. High-voltage and extra-high-voltage (EHV) generators must be able to provide reactive power in one of the fixed reactive power ranges if their active power exceeds 20% of their total installed capacity.

One common feature is that when small active powers are introduced, the reactive power requirements are minimal or non-existent. The different reactive power requirements are summarized in Figure 1.

Selected case studies

In Germany, the case study focuses on the forecasting of the reactive power flexibility potential of medium voltage (MV) photovoltaic power plants. The study evaluates different PV forecasting approaches and introduces a reliability index to assess the accuracy of reactive power flexibility forecasts. This highlights the need for high forecast reliability to prevent overestimation and investigates the use of a reactive power planning reserve to increase forecast reliability. This applies in particular to periods of low active power inflow, as mentioned in the previous section, and highlights the importance of continuous grid code updates, as indicated in the PV ancillary services report for Task 14.

Japan’s approach includes evaluating voltage control performance in different scenarios, taking into account the growing penetration of PV. A study by a consortium involving TEPCO Power Grid and Waseda University, supported by NEDO, evaluated voltage control with constant power factor control. The results led to a new grid code in 2023 stipulating that power factor settings must be adaptive based on DSO requests, emphasizing the need for flexible control strategies.

The Austrian study focused on the effectiveness of future grid-related measures in low-voltage networks. Different scenarios were assessed, including the impact of climate policies, regional technology implementations and different operational strategies related to PV, heat pumps and e-mobility. The study identified challenges such as the need for detailed analysis of Q(V) control contributions and the lack of large-scale network simulation capabilities, which hinder a comprehensive understanding of the value of reactive power management in distribution networks.

The most important conclusions from the report

The report’s lead authors highlight three key conclusions. First, there is a need for an updated regulatory framework to adapt to the changing energy landscape, ensuring the resilience and efficiency of energy systems. Second, the potential of DERs as a source of reactive power services should be further explored, including increased integration of solar PV forecasting. Third, cooperation between transmission system operators (TSOs) and DSOs is essential for effective reactive power management, which could be improved through information and communication technology (ICT).

Completion of Task 14 and Future Directions

Task 14 was completed after 14 years of successful research and development in the field of PV integration and reactive power management. Over the three phases, Task 14 made significant progress in resolving technical challenges, developing standards, and promoting best practices for high penetration of PV systems in power grids. At the end of Task 14, its legacy continues to influence grid management and renewable integration strategies.

Looking ahead, Task 19 will begin in 2025 as a continuation of Task 14, building on its achievements and continuing its mission to enhance grid stability and efficiency through increased integration of renewable energy. Task 19 will focus on managing grids with 100% renewable energy sources, integrating photovoltaics with wind and defining the role of photovoltaics in the smart grid.

More information on Task 14 of the IEA PVPS programme and all its publications can be found here.