0093-9994 (c) 2018 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TIA.2018.2878155, IEEE Transactions on Industry Applications Replacing diesel generators with hybrid renewable power plants: Giglio Smart Island project F. Palone, P. Portoghese, L. Buono, A. Necci Engineering dept. Terna S.p.A. Roma, Italy francesco.palone@terna.it F.M. Gatta, A. Geri, S.Lauria, M. Maccioni DIAEE Sapienza University Roma, Italy marco.maccioni@uniroma1.it Abstract—The use of diesel generators to supply electricity to small remote islands is both costly and environmentally troublesome. On the other hand, small island networks pose peculiar stability and reliability problems when renewable energy sources are added. The paper regards the installation of an hybrid power plant (phortovoltaic, PV, plus lithium battery and synchronous condenser) in Giglio island, to replace existing diesel units. The paper discusses the general overview of the project and presents steady-state and dynamic simulations of the proposed energy system. Results evidence the advantages of the proposed Giglio hybrid power plant over existing diesel generators in terms of reduction of both pollution and energy costs, also allowing to fulfill the N-1 network security criterion. At the same time, results underline the need to install a properly sized flywheel in order to assure the stability of supply. Keywords—Remote islands; Smart Island; PV plant; Battery energy storage system; Synchronous condenser. I. INTRODUCTION The small Giglio island (21.2 km 2 ) lies in the Tyrrhenian Sea (NW Mediterranean), about 28 km off the Italian coast. Despite a resident population not exceeding 1,500, tourist influx in summer raised electric consumption to a 3.4 MW peak demand, also including the operation of a 500 kW desalination plant. For comparison, the total energy consumption is about 10 GWh on a yearly base (2013 data). As the whole load is supplied by diesel generators, with inherently high fuel cost (mostly transportation cost) and relatively low efficiency, energy costs are high in Giglio, up to 430 €/MWh [1]. Although renewable energy production is significantly growing in Italian mainland thanks to the incentives for photovoltaic (PV) and wind power plants, it is necessary to adopt a different paradigm for enabling renewable penetration in small isolated networks, due to their peculiar characteristics. TERNA (the Italian Transmission System Operator) launched its “Smart Islands” project, with the aim of replacing local diesel generators with renewable energy sources (RESs) on the islands of Giglio [2], Pantelleria and Giannutri [3]. The aim was to fulfill the target values fixed by the Italian ministerial decree DM 14/02/2017 regarding the development of renewable energy sources in small islands (for Giglio Island, the target for year 2020 is to replace at least 20% of diesel generation with RESs). Similar initiatives have been developed in other countries, for instance in Greenland as described in [4]. The first implementation of the TERNA “Smart Island” project regards Giannutri Island, as described in [3], and has been commissioned in 2018. The Giglio Smart Island project includes two stages: 1. Installation of a 500 kWp photovoltaic power plant in Allume locality (plus several small distributed PV plants accounting for about 200 kWp) and a 1000 kW / 500 kWh lithium-ion battery energy storage system (BESS). First stage target is a 7% reduction in diesel fuel consumption. 2. Installation of distributed PV plants and of an additional BESS in order to achieve an overall 30% fuel consumption reduction. The paper describes the Giglio Smart Island project, dealing with technical issues and criticalities related to the integration of RESs in such a small electric power system. In conjunction with the Giannutri Smart Island project described in [3], it can be also intended as a general outline of the TERNA “Smart Islands” Project. PV and BESS sizing are discussed in Section II; relevant operation and control strategies are described in Section III. The hybrid power plant layout and nameplate data of main equipment (BESS, power conditioning system (PCS) [5], transformers, synchronous condenser) are reported in Section IV. Steady state simulation results are summarized in Section V, whereas Section VI deals with the dynamic behavior of the system. Conclusions are finally reported in Section VII. II. PV AND ENERGY STORAGE SIZING The size of both PV plant and BESS was chosen based on the Giglio island yearly load profile and the output pattern of a PV plant located not far on the mainland, in Tuscany. Both time series were sampled on a 15 minutes basis. A. Load requirement As anticipated, the Giglio island power demand has a wide seasonal variation, ranging from a 230 kW minimum in December to a 3.4 MW peak in August (the yearly average is