In early 2021, Eurelectric releases a landmark study on distribution grid investment needs at the EU level by 2030, conducted by Monitor Deloitte in partnership with E.DSO, entitled ‘Connecting the dots’, see also here: https://www.eurelectric.org/connecting-the-dots/

With the increasing penetration of variable renewable energy sources based on inverter-connected technologies, the system non-synchronous penetration (SNSP) metric has been used in several power systems to describe, in simple terms, the extremities of operation and reduced reliance on traditional synchronous generators. It has provided an effective operational tool to monitor power system security, as well as provide an indicator of the long-term progression towards higher penetrations of inverter based resources (IBR). The metric can be easily calculated in both operational and planning timeframes, providing a useful tool in a variety of settings. However, it is potentially misleading to compare SNSP values derived from different power systems which may use a diverse range of solutions to manage system security issues including inertia and system strength. On this premise, this paper discusses the SNSP metric and its applications in the Australian National Electricity Market (NEM). Scenarios are considered where the metric can be used effectively and where caution is required. An alternative form of SNSP that may be more representative of the operational state of renewables-rich and technology diverse power systems is also proposed.

Purpose: Within the context of the innovative research project “Citizen Energy Transition”, subsidized by the Ministry of Science, Research and the Arts Baden-Wuerttemberg (funding code Kap. 1403 title group 75), digital business models for the economic, platform-based marketing of PV power will be developed and implemented by 2022. The fundamental problem addressed in this research project is to ensure the continued operation of renewable energy systems, which are no longer eligible for funding under the Renewable Energy Sources Act (EEG). The withdrawal of renewable energy intallations from the EEG funding since 1 January 2021 and the resulting possible shutdown are likely to lead to a breakdown of renewable energy generation capacities. This would be problematic from the perspective of the climate protection, but also with reference to the consistent implementation of the energy transition. Therefore, it is all the more important to develop sustainable business models for community energy cooperatives, operators of renewable energy systems, electricity consumers, network operators, direct marketers, billing service providers and small and medium-sized municipal utilities.

Design/Methodology/Approach: In order to implement user-experienced business models, a hypothesis-based survey of all citizens' energy cooperatives (full survey) in Baden-Wuerttemberg was carried out in this research project in spring 2021. The aim of this empirical survey was to explore the current situation and options for action of the citizens' energy cooperatives with regard to the discontinued EEG remuneration for PV systems. Within the context, empirical findings from the customer survey are presented and conclusions are derived.

Findings: By evaluating this survey, key conclusions could be drawn for the development of new, innovative platform-based marketing approaches for the energy generated from renewable energy systems. Amongst other things, it was found that the current business model of the citizens' energy cooperatives is mainly based on the pure generation of renewable electricity, which is marketed within the framework of the EEG.

Originality/Value: The research team developed a hypothesis-based questionnaire to empirically identify the needs of citizens' energy cooperatives and thus be able to create platform-based and service-oriented business models. With this in mind, the innovative business models have the aim of enabling the citizens' energy cooperatives and the energy companies to continue to exist in a mutually meaningful cooperation.

A large number of distributed energy resources (DER) using renewable energy, such as solar power generation and wind power generation, and battery storage systems (BESS), have been introduced. Those are connected to power grids via power electronic inverters. However, unlike synchronous generators, the inverters do not have inertia and synchronization power, which are necessary for maintaining power system stability during and after power system disturbances. The authors have researched grid-forming inverter control (GFM) to provide virtual inertia and virtual synchronization power to the grid-connected inverter. This paper proposes an overcurrent suppression control method for the GFM inverter and shows a Simulink simulation model of the GFM inverter. The paper also reports the results of simulations for evaluating the proposed overcurrent suppression control method.

In future power systems voltage and frequency will mainly be formed by synchronous inverter-based power plants with advantageous capabilities compared to today's synchronous machines. This paper introduces a synchronous energy storage system solution (SESS) with grid forming capabilities for voltage, angle and frequency strength improvement in distribution and transmission networks. Configurable control modes for inertia and damping provision are presented. Application examples and performance capabilities for inertia, instantaneous fault current, power oscillation response as well as power reserve provision are shown based on simulation results and practical laboratory experiments. The challenges for accelerated grid integration of SESS are outlined as well.

One of the main challenges associated with deployment of high shares of inverter-based resources (IBRs) in power grid is not only reduced system inertia but also degrading system strength that may cause severe stability impacts. A minimum level of system strength is needed for the power system to remain stable. Significant system strength reduction is expected in almost all planned areas for solar and wind generation deployment. Synchronous condensers (SC) have been considered as one main technology to address the system strength issues for the areas with high levels of IBRs. SCs can help improving reliability and resiliency of power system but they do not provide the full range of services needed by power systems for reliable and economic integration of high shares of inverter-coupled variable generation such as PV generation. NREL has been conducting research on a hybridized concept that combines SCs with grid forming (GFM) battery energy storage systems (BESS). This super flexible AC transmission system (SuperFACTS) that combines these two technologies in a single plant under the same controller offers a unique scalable set of services to the power system at all levels (transmission, sub-transmission, distribution, islands and isolated microgrids).

The following research presents an optimal control framework called Oxtimal that facilitates the efficient use and control of photovoltaic (PV) solar arrays. This framework consists of reduced order models (ROM) of photovoltaics and DC connection components connected to an electric power grid (EPG), a discretization of the resulting state equations using an orthogonal spline collocation method (OSCM), and an optimization driver to solve the resulting formulation. Once formulated, the framework is validated using realistic solar profiles and loads from actual residential applications.

In the LINDA project a control approach for island grids was developed which enables the use of renewable energy sources during emergency power supply. A black start unit sets up an island grid. To find proper parameters for the controller of the black start unit, knowledge about the static and dynamic behaviour of the distribution grid, induced by fluctuations of voltage and frequency, is essential. During the research project LINDA 2.0, supported by the German Ministry for Economic Affairs and Energy, this concept of applying an emergency power supply should be transferred to other grid areas. To get an actual database about the aggregated grid behaviour, a mobile generator will be used during grid maintenance work to determine the parameters for a frequency and voltage dependent model of the supplied sub-networks. The measurement procedure and control concept for the mobile generator is introduced in this paper.

This paper presents a different approach for shortcircuit analysis of grid-connected photovoltaic (PV) power plants, where several Voltage Source Converters (VSCs) are adopted to integrate PV modules into the grid. The VSC gridsupport control and various potential current-saturation states are considered in the short-circuit calculation. In particular, the studied system is modeled using a flexible formulation that includes the converter equations in both normal operation and fault conditions. Then, two different methodologies are proposed for short-circuit calculation with different options regarding the existence of multiple equilibrium points involving different converters current-saturation states. Case studies have been presented for the system with different numbers of PV inverters.

The large-scale integration of variable renewable energy (RE) into the electricity mix imposes to deal with the uncertainty and variability associated with such generation. As a result, the power system reserve management, which aims to ensure real-time balancing between production and load, has to evolve in order to guarantee the reliable operation of the electrical grid. This paper focuses on the evaluation of advanced reserve sizing methods identified in the literature, based on real operation data, from RE plants under operation. More precisely, the paper details a field-data oriented analysis, where fine time-resolution (few minutes time step) data is analyzed (1) to characterize RE variability and uncertainty, and (2) to evaluate the benefits from taking into account such variability and uncertainty for advanced reserve sizing.