Economic analysis of residential PV self-consumption systems with Li-ion batteries under different billing scenarios Carlos Galilea, Julio Pascual, Alberto Berrueta, Alfredo Ursua, Luis Marroyo Department of Electrical, Electronic and Communication Engineering Institute of Smart Cities (ISC) Public University of Navarre (UPNA) Pamplona, Spain carlos.galilea@unavarra.es Abstract—In this paper, an economic analysis for four houses with a PV self-consumption system with and without Li-ion batteries is carried out. In particular three different ways of sizing PV and batteries are analyzed under three different billing scenarios for the compensation of surplus energy injected into the grid. All methods run under the same energy strategy, which maximizes self-consumption. The three billing scenarios are: (1) no retribution for surplus energy, (2) retribution at pool price (net billing), and (3) monthly net metering. This study shows how fixed costs make these systems just profitable for small systems. Moreover, the results show how the battery cost and lifespan affects the final profitability of the system and what future evolution in these factors is needed for making these systems profitable under different billing methods. Keywords—PV self-consumption, battery storage, net- metering, net-billing, distributed generation, prosumer, economic analysis I. INTRODUCTION There is an increasing concern worldwide to tackle global warming by different means, including the use of less fossil fuels by combining energy efficiency methods and integrating more renewable energies into the system. At the 2012 United Nations Climate Change Conference, in Doha, the Kyoto [1] protocol was extended until 2020 and later on, at the Paris Agreement [2], some specific goals were set being now put in practice by regions and countries involved. For instance, these ambitions are reflected in different governmental plans in Europe [3], [4] and Spain [5], [6], in order to have a more renewable energy system. These plans include the residential sector, changing the energy generation model to a more distributed one, by installing renewable energy sources in buildings, sometimes with energy storage and an energy management system (microgrids) [7]–[9]. These policies along with the continuous rise of electricity prices and the cost reduction of renewable energy costs, especially photovoltaic (PV) power, which has reach grid parity in many regions [10], has brought worldwide interest to final users to install such systems in their homes [11]. However, in Spain, due to Government opposition at first and later instability, there has been great uncertainty on the way self-consumption is to be regulated. This uncertainty is slowing down the adoption of self-consumption in the residential sector given that these systems constitute a long-term investment and whose optimal sizing depends critrically on the legal regulation. Several studies exist on this topic for former regulations in Spain [12], [13], and billing systems in European countries [14] including Spain [15], [16], with batteries [17] and considering net metering [18]. In this study, different sizing and regulations are compared under otherwise same conditions in order to understand the best sizing solutions for each case, stressing the importance of a stable regulation frame for the optimal design of these long-term systems. Furthermore, the key factors for the profitability of these systems are analyzed. Note that different consumption profiles are analyzed under different billing systems and sizing methods, permitting to understand their influence in profitability. In particular, in Section II, the case studies, prices, sizing methods and billing methods are described. Moreover, the base cases, i.e., the houses without self-consumption, are analyzed in terms of electricity billing. In Section III, the results for the profitability of every system under all the sizing and billing methods are shown and analyzed. Finally, in section IV, the major conclusions are presented. II. PROBLEM STATEMENT A. Case studies All four single-family homes analyzed (named A to D) are located in Pamplona (Spain). Hourly power consumption profiles from year 2017 are available for the analysis. The total consumption over the year of these homes ranges from 2980 to 5115 kWh, being around the national average in the residential sector [19]. The annual bill for these cases without the self-consumption system serves as the reference case against which the rest of the cases will be compared. Besides, the characteristics of the roofs are known which permits to calculate the PV power available during the year for every case. B. PV and battery sizing The analysis has been carried out considering three PV and battery sizing options shown in Table I. TABLE I. SIZING OPTIONS CONSIDERED FOR ANALYSIS PV power [kWp] Battery capacity [kWh] Sizing I EPV year ≡ 120% Econs year 80% Ēcons day Sizing II EPV year ≡ 90% Econs year 20% Ēcons day Sizing III EPV year ≡ 120% Econs year 0 Almacenamiento Renovable Avanzado de Litio para Autoconsumo Residencial interconectado (ARALAR) ‒ 0011-1411-2017-000021, Proyecto de I+D Gobierno de Navarra, and Hibridación de tecnologías avanzadas de almacenamiento eléctrico para sistemas basados en energías renovables DPI2016-80642-R (HIBRITAER)