Thomas Stetz

Mittelhessen University of Applied Sciences | THM · Smart Grids and Energy Storage

This article is a reprint from T. Stetz, J. von Appen, F. Niedermeyer, G. Scheibner, R. Sikora and M. Braun, "Twilight of the Grids: The Impact of Distributed Solar on Germany’s Energy Transition," in IEEE Power and Energy Magazine, vol. 13, no. 2, pp. 50-61, March-April 2015, doi: 10.1109/MPE.2014.2379971. Please access the original article on IEE...

In strategic electrical power systems planning, defining new power line routes is a complex task. The preferred solution has not only to comply with voltage and current constraints under given load scenarions, but also to avoid unnecessary high investment costs due to a non-optimal routing. This paper aimes to improve automated power systems planni...

This paper presents a methodology for the evaluation of unused photovoltaic (PV) rooftop potential while taking into account the technical constraints which define a grids’ hosting capacity. It is the goal of this paper to show how much additional PV generation (in kWp and kWh/a) could be installed on specific roofs without triggering grid reinforc...

In recent years, the number of active grid components for voltage regulation in distribution grids has increased significantly. Besides voltage regulators (VRs), such as transformers with On Load Tap Changers (OLTCs), distributed generators can provide a certain voltage support by means of reactive power control (RPC). The different control entitie...

The Management Summary has been prepared by the IEA-PVPS Task 14 Subtask 2 leader Fraunhofer IWES (Germany) with valuable contributions from several IEA-PVPS Task 14 members and other international experts: Barry Mather (NREL, USA), Benoît Bletterie (AIT, Austria), Pieter Vingerhoets (KU Leuven, Belgium), Kenn Frederiksen (Kenergy, Denmark), Kazuhi...

This paper presents recommendations for an effective commissioning and operation of distributed generators (DGs), focussing on the aspect of reactive power control for static voltage support. Error-sensitive tasks in the process chain from commissioning to operation are revealed, based on first-hand field experience of major German and Austrian dis...

Changing reactive power behaviors of distribution systems (e.g., due to higher degrees of cabling and local reactive power provision through distributed generators (DGs)) together with the loss of generator-based reactive power sources at transmission system level may lead to an increased demand of reactive power flexibilities in the distribution g...

Due to high renewable energy share in the distribution networks, reverse power flows can be observed, leading to challenges for the distribution network perators (DNOs). In case of high photovoltaic (PV) penetration in low voltage (LV) level, the LV networks are susceptible to voltage violations and overloading problems, especially at peak feed-in...

The topic of providing controllable reactive power (CQ) to the next-higher voltage level based on controlling distributed energy resources (DER) has recently received increasing attention. From a theoretical perspective, the use case of deferring or avoiding Extra High Voltage (EHV) investment in compensating equipment by the ancillary service 'pro...

In this paper, the impact of voltage support by PV systems, installed at LV level, on the reactive power exchange at the HV/MV connection point is presented. The analysis was performed using a detailed system model of the smart grid re-gion Seebach (south-eastern Bavaria), encompassing LV and MV level. The simulations were performed for different v...

In dieser Veröffentlichung wird ein zentrales Regelungsverfahren vorgestellt, welches die Erfüllung von Blindleis-tungsvorgaben des Hochspannungsnetzbetreibers am 110 kV-Netzverknüpfungspunkt (NVP), mittels gesteuerter Blind-leistungsbereitstellung durch dezentrale Erzeugungsanlagen (DEA) in der Mittelspannungsebene ermöglicht. Das vor-geschlagene...

After booming from 2009 to 2012, the German photovoltaic (PV) industry suffered from drastically reduced feed-in tariffs (FITs). With around 3 GWp of newly installed nominal PV capacity in 2013 and a predicted drop to around 2 GWp of additional nominal capacity in 2014 (there had only been 1.03 GWp added by July), the growth of the German PV market...

Executing quasi-static time-series simulations is time consuming, especially when yearly simulations are required, for example, for cost-benefit analyses of grid operation strategies. Often only aggregated simulations outputs are relevant to grid planners for assessing grid operation costs. Among them are total network losses and power exchange thr...

The massive deployment of grid-connected PV in recent years has brought PV penetration in the electricity grids to levels where the conventional fit-and-forget approach to interconnecting PV reaches its limits. In many cases, constraints and limitations of existing electricity infrastructure already have evolved to one of the key barriers delaying...

As the business case for home-scaled PV storage systems emerges in Germany, the impact of different control strategies for such systems on the distribution grid has to be evaluated. This paper assesses the economic performance of two different control strategies for PV storage systems (optimization- and rule-based) regarding their ability to minimi...

During the past four years, national experts from 11 institutions around the world have worked together within Subtask 3 – High penetration solutions for central PV generation scenarios – in order to identify best practice scenarios for a technically and economically improved grid integration of PV focusing on aspects at a power system level. The s...

During the past four years, national experts from thirteen institutions around the world have worked together within the International Energy Agency (IEA) PVPS Task 14 Subtask 2 – High Penetration PV in Local Distribution Grids. The main aim of this collaboration was to identify industry’s best practices for achieving high penetration levels of PV...

First, we investigate the technical and economic potential of autonomously operating voltage control strategies in low voltage grids with high photovoltaic penetration. The investigated control strategies are based on the reactive power control capabilities of modern photovoltaic inverters and the application of distribution transformers with on-lo...

Im Verteilnetzbetrieb werden neben den Verteilnetztransformatoren zunehmend dezentrale Erzeuger, wie Photovoltaikanlagen, an der Spannungshaltung aktiv beteiligt. Zur Sicherstel-lung eines qualitativ hochwertigen Netzbetriebs sind ungewollte wechselseitige Beeinflus-sungen von PV-Anlagenregelung und Transformatorregelung auszuschließen bzw. auf ein...

In Niederspannungsnetzen mit hohem Anteil dezentraler Energieerzeugungsanlagen ist die Einhaltung des zulässigen Spannungsbands nach DIN EN 50160 eine der Hauptherausforderungen zur Sicherung einer zuverlässigen und qualitativ hochwerti-gen Energieversorgung. Auch Photovoltaikanlagen niedriger Leistungsklassen kön-nen durch Maßnahmen zur lokalen Sp...

Local PV storage systems are emerging in Germany as PV feed-in tariffs have dropped below electricity prices for households. These PV storage systems provide the opportunity to increase the local consumption of locally generated PV energy. The so called self-consumption does not imply an explicit benefit for highly PV penetrated distribution grids...

A major issue for distribution system operators is to maintain voltage quality in their networks. This holds especially for networks with high local PV penetration. In times of high solar irradiation, reverse power flows can lead to voltage rises and violations of voltage limits at critical nodes. Inverter-based autonomous voltage control strategie...

This thesis analyzes the technical and economic potential of autonomous voltage control strategies for improving distribution grid operation with high shares of photovoltaic (PV) generation. Key issues include: The simultaneity of local photovoltaic generation and local consumption as well as its influence on reverse power flows. The theoretical p...

Technically effective and economically efficient voltage control is a major issue in distribution systems with high amounts of installed capacity from dispersed generators, such as photovoltaic. In this paper, the results of an encompassing cost–benefit analysis for different voltage control strategies are presented. The investigated voltage contro...

In this study, technical and economical investigations of different autonomous voltage control strategies are conducted for biogas plants with an electrical nominal power of some 100 kWel. For the assessments, a detailed model of a common biogas CHP plant with its usual electrical characteristics is deduced. Based on root mean square simulations in...

In this study, technical as well as economic aspects of local and central coordinated voltage control strategies, which are based on reactive power provision from the distributed generators, will be analyzed in the context of high penetration of renewable energy resources in European medium voltage distribution networks. An economical evaluation of...

In diesem Beitrag wird untersucht, wie sich die lokale Spannungsregelung des Um-spannwerks-Transformators und die Blindleistungsregelung der Photovoltaikanlagen gegenseitig beeinflussen können. Es werden mögliche ungewollte Wechselwirkun-gen für den Netzbetrieb dargestellt. Für die Untersuchung wird ein spannungsebe-nen-übergreifendes Simulationsmo...

Energy supply systems are facing significant changes in many countries around the globe. A good example of such a transformation is the German power system, where renewable energy sources (RESs) are now contributing 25% of the power needed to meet electricity demand, compared with 5% only 20 years ago. In particular, photovoltaic (PV) systems have...

The installed capacity of photovoltaic systems has recently increased at a much faster rate than the development of grid codes to effectively and efficiently manage high penetrations of PV within the distribution system. In a number of countries, PV penetrations in some regions are now raising growing concerns regarding integration. Management stra...

This work discusses the technical and economical benefits of different active and reactive power control strategies for grid-connected photovoltaic systems in Germany. The aim of these control strategies is to limit the voltage rise, caused by a high local photovoltaic power feed-in and hence allow additional photovoltaic capacity to be connected t...

With the tremendous increase in installed capacity of renewable energy resources in Germany, distribution network operators are facing reverse power flows and voltage violations. Different control approaches for controllable network components and distributed energy units exist to maintain secure and reliable grid operation. This conference contrib...

This paper shows how an additional provision of reactive power influences the economically optimized sizing of inverters for photovoltaic systems in Germany. At first, the results of an encompassing survey among 934 photovoltaic system operators show the current inverter sizing experiences for a region in South-East Bavaria. In a second step an ana...

With the tremendous increase in installed capacity of renewable energy resources in Germany, distribution network operators are facing reverse power flows and voltage violations. Different control approaches for controllable network components and distributed energy units exist to maintain a secure and reliable grid operation. This conference contr...

Derzeit werden in Deutschland im Rahmen der Überarbeitung der technischen Richtlinie "Erzeugungsanlagen am Niederspannungsnetz" Möglichkeiten diskutiert, wie Photovoltaikanlagen auf der Niederspannungsebene an der Spannungshaltung, zum Beispiel durch die lokale Bereitstellung von Blindleistung, beteiligt werden können. Durch diese zusätzlichen Maßn...

As a reaction to the steadily increasing share of photovoltaic (PV) power, German utilities are working on a new standard for the connection and parallel operation of generators in low voltage networks. The new grid code could be a big step towards active participation of PV-Systems in low voltage network operation. Reactive power provision by PV s...

The German Renewable Energy Sources Act 2009 contains a first step towards domestic energy management. The Franco-German project "Sol-ion" develops and analyses a PV-battery system for this application. This conference paper focuses on investigating the influence of possible high installation rates of this system on the German low voltage distribut...

In this paper the economically optimized inverter sizing is determined for PV inverters which have to provide reactive power. A PV module model and a PV inverter model were developed in Matlab®, based on real one-year solar irradiation profiles provided by Meteonorm® and recorded at Fraunhofer IWES test sites. The single cost categories of a PV inv...

Power quality and reliability are two very important factors in electrical power supply, particularly for specific branches of industry. "Multifunctional Photovoltaic Inverters" with storage units at the direct current link of the photovoltaic inverter can substitute uninterruptible power supply systems. Installed in industrial facilities, this typ...