eeh power systemslaboratory

Vasileios Poulios

Optimal placement and sizing of battery storageto increase the PV hosting capacity of low

voltage grids

Master ThesisPSL1428

EEH Power Systems LaboratorySwiss Federal Institute of Technology (ETH) Zurich

Expert: Prof. Dr. Goran AnderssonSupervisors: Dr. Florian Kienzle, Dipl.-Ing. Evangelos Vrettos

Zurich, December 11, 2014

Preface

In 2008, the majority of the citizens of Zurich voted in favour of the implementationof the 2000-Watt society concept, an environmental vision introduced by ETH. The2000-Watt society concept refers both to the reduction of the overall continuous energyusage to no more than 2000 Watts per person, as well as to the reduction of the carbonfootprint to no more than 1 tone CO2 equivalent per person by 2050. As of 2015 ,ewz, the electricity distribution company of Zurich, with its product ewz.solarzuri, isoffering to its customers the opportunity to co-finance the construction of photovoltaic(PV) plants in their neighbourhood and receive their respective share of the producedelectricity during the plants lifetime.

In this context, the PV penetration in the distribution grid of the city of Zurich is ex-pected to rise with a growing pace over the next years. This can bring challenges to theexisting electricity grid infrastructure and lead to the violation of several technical con-straints such as voltage band and transformer or cable loadings. Moreover, the expectedincrease in the number of electrical vehicles can also push the existing distribution gridto its limits.

From the distribution system operators (DSO) point of view, the conventional way ofintegrating considerable amounts of distributed generation and electric vehicles wouldrequire significant investments for the network reinforcement and expansion. The instal-lation of battery storage in the low voltage level is an interesting alternative for solvingthe aforementioned technical problems and could therefore avoid or at least reduce orpostpone, the need for extensive conventional network reinforcements. The decreasingbattery prices together with the plethora of versatile services that a battery system canoffer are rendering this solution more and more attractive for the electricity utilities.Already, various projects involving battery storage as a PV integration measure are run-ning, such as the pilot project of ewz in Dora-Staudinger-Strasse, where the behaviourof a battery system in conjunction with PV plants will be studied.

This thesis will address the question What is the cost-optimum battery storage alloca-tion in order to integrate the full PV potential of a LV grid area?. Furthermore, theeffect of Active Power Curtailment (APC) as a PV integration measure in combinationwith battery storage will be examined from a DSO perspective.

i

Abstract

The purpose of this thesis is to investigate the cost-optimal placement and sizing ofbattery storage as a PV integration measure in the distribution grid level. Addition-ally, potential synergies between PV generation, battery storage, smart PV curtailmentand electric mobility are also explored within this thesis. Accordingly, a versatile opti-mization tool has been developed in order to identify potential battery location and sizecombinations that increase the PV hosting capacity of a low voltage grid at minimumcost. The optimization tool is based on the two basic Optimal Power Flow (OPF) algo-rithms: AC OPF and DC OPF. The high computation times that an AC OPF requires,as well as the many simplifications assumed in the DC OPF, necessitate the developmentof hybrid methods that render the optimization problem tractable without neglectingcrucial operational data (e.g. voltages).

In the project PV Leimbach, ewz compares potential PV integration measures on atechnical as well as economic basis. In this context, one substation area of Leimbach ischosen for the demonstration of the optimization tool in a real network. Measurementdata from a local transformer station and PV plants in the city of Zurich for 2013 areutilized as inputs for the optimization. Moreover, scenarios including electric mobilityload curves extracted by a model developed at ETH Zurich are also investigated.

The functionality and the performance of the developed methods is assessed for a bench-mark network of reduced size and a single method that provides the best trade-off be-tween computational time efficiency and accuracy of the results is chosen for implemen-tation on the real case-study network. The cost optimal battery storage placement andsizing is investigated, while the battery storage dispatch is assessed by a second opti-mization algorithm that aims at the maximization of the degree of self-sufficiency ofthe LV grid area. In the second part of the simulations, various sensitivity analyses arecarried out to investigate different scenarios and parameter combinations.

The results of this work show that a DSO would have to bear considerable costs in casethe problems caused by PV penetration are addressed exclusively by battery storageinstallation. The implementation of even low curtailment levels could result to a drasticreduction of these costs with negligible energy losses. Assuming a high PV penetration,a similar reduction of the required battery capacity results with the introduction of ahigh share of electric cars. Finally, it can be concluded that the implementation of hy-brid AC and DC OPF methods for battery placement and sizing problems can lead to

ii

iii

a significant decrease in computation time without sacrificing crucial information aboutthe network.

Key Words: optimal battery sizing and placement, optimal battery dispatch, PV pen-etration, active power curtailment (APC), electromobility, LV network, hybrid OPFmethods.

Kurzfassung

Der Zweck dieser Masterarbeit ist es, die kostenoptimale Platzierung und Dimension-ierung des Batteriespeichers als PV-Integrationsmassnahme auf Verteilnetzebene zu un-tersuchen. Uberdies werden in dieser Masterarbeit potenzielle Synergien zwischen derPV-Erzeugung, dem Batteriespeicher, der PV-Abregelung und Elektromobilitat analysiert.Entsprechend wurde ein vielseitiges Optimierungswerkzeug entwickelt, um verschiedeneMoglichkeiten in Bezug auf Batterieposition und -grosse zu uberprufen, um so die PV-Aufnahmekapazitat eines Niederspannungsnetzes mit minimalem Kostenaufwand zu ver-grossern. Das Optimierungswerkzeug basiert auf den zwei grundlegenden optimalenLastflussalgorithmen: AC OPF und DC OPF. Die hohen Berechnungszeiten, die ein ACOPF erfordert wie auch die vielen Vereinfachungen, die im DC OPF angenommen wer-den, erfordern die Entwicklung von hybriden Methoden, die das Optimierungsproblemlosbar machen ohne entscheidende betriebliche Daten (z.B. Spannungen) zu vernachlas-sigen.

Im Projekt PV Leimbach vergleicht ewz potenzielle Integrationsmassnahmen auf einertechnischen wie wirtschaftlichen Basis. In diesem Kontext wird ein Niederspannungsnet-zgebiet von Leimbach fur die Demonstration des Optimierungswerkzeugs in einem echtenNetz ausgewahlt. Messdaten einer lokalen Trafostation und von PV-Anlagen der StadtZurich von 2013 werden fur die Optimierung verwendet. Zusatzlich werden weitereSzenarien in die Untersuchungen miteinbezogen wie beispielsweise Elektromobilitats-Lastkurven aus einem an der ETH Zurich entwickelten Modell.

Die Funktionalitat und die Performance der entwickelten Methoden werden fur einBenchmarknetz von reduzierter Grosse evaluiert. Im Anschluss wird die Methode, welcheden besten Kompromiss zwischen Berechnungszeiteffizienz und Genauigkeit der Ergeb-nisse erzielt, fur die Durchfuhrung im echten Fallstudiennetz gewahlt. Die kostenopti-male Platzierung und Dimensionierung der Batteriespeicher wird untersucht, wahrendder betriebliche Batteriespeichereinsatz durch einen zweiten Optimierungsalgorithmusbewertet wird, der auf die Maximierung des Grads der Unabhangigkeit des Niederspan-nungsgebiets abzielt. Im zweiten Teil der Simulationen werden verschiedene Sensitiv-itatsanalysen ausgefuhrt, um verschiedene Szenarien und Parameterkombinationen zuuntersuchen.

Die Ergebnisse dieser Arbeit zeigen, dass ein Verteilnetzbetreiber betrachtliche Kosten

iv

v

tragen musste, wenn die durch die PV-Einspeisung verursachten Probleme ausschliesslichdurch die Installation von Batteriespeicher gelost werden mussten. Die MoglichkeitPV-Anlagen in geringem Mass abzuregeln konnte zu einer drastischen Verminderungdieser Kosten fuhren, ohne uber das ganze Jahr betrachtet wesentliche Energieverlustezu verursachen. Unter der Annahme einer hohen PV-Einspeisung, resultiert eine ahn-liche Verminderung der erforderlichen Batteriekapazitat aufgrund der Einfuhrung eineshohen Anteils von elektrischen Autos. Es kann festgehalten werden, dass die Anwen-dung von hybriden AC und DC Methoden fur Batterieplatzierung und Dimensionierungzu einer bedeutenden Abnahme in der Berechnungszeit fuhren kann, ohne entscheidendeInformationen uber das Netz zu verlieren.

Schlusselworter: optimale Platzierung und Dimensionierung des Batteriespeichers,optimaler Batteriespeichereinsatz, PV-Einspeisung, PV-Abregelung, Elektromobilitat,Niederspannungsnetz, hybride OPF-Methoden.

Acknowledgement

This master thesis was carried out in the Power Systems Laboratory (PSL) at ETHZurich in cooperation with the grid design department of ewz, the utility of the city ofZurich. Having spent the last six months working on this thesis there are a lot of peopleI wish to thank:

I would like to express my deepest gratitude to my supervisors Dr. Florian Kienzle fromewz and Evangelos Vrettos from ETH Zurich for their aspiring guidance and encourage-ment throughout this project. This work could not have been conducted without th