energies Article Impact of Energy Losses Due to Failures on Photovoltaic Plant Energy Balance Isidoro Lillo-Bravo 1, * ID , Pablo González-Martínez 1 ID , Miguel Larrañeta 2 ID and José Guasumba-Codena 3 1 Department of Energy Engineering, Universidad de Sevilla, Camino de los Descubrimientos s/n, 41092 Seville, Spain; pabgonmar1@gmail.com 2 Andalusian Association for Research and Industrial Cooperation (AICIA), Camino de los Descubrimientos s/n, 41092 Sevilla, Spain; mlarraneta@gter.es 3 Renewable Energy Laboratory, Universidad de las Fuerzas Armadas, 171103 Sangolquí, Ecuador; sjguasumba@espe.edu.ec * Correspondence: isidorolillo@us.es; Tel.: +34-954-487-236 Received: 13 December 2017; Accepted: 29 January 2018; Published: 3 February 2018 Abstract: Photovoltaic (PV) plant failures have a significant influence on PV plant security, reliability, and energy balance. Energy losses produced by a PV plant are due to two large causes: failures and inefficiencies. Knowing the relative influence of energy losses due to failures and energy losses due to inefficiencies on the PV plant energy balance contribute to the optimization of its design, commissioning, and maintenance tasks. This paper estimates the failure rates, grouped by components, and the relative impact of the failures on the PV plant energy balance through real operation and maintenance follow-up data of 15 PV plants in Spain and Italy for 15 months. Results show that the influence of failures in energy losses of all analysed PV plants is low, reaching a maximum value of 0.96% of the net energy yield. Solar field energy losses only represent 4.26% of all failure energy losses. On the other hand, energy losses due to inefficiencies have represented between 22.34% and 27.58% of the net energy yield. Keywords: photovoltaic (PV); energy losses; failures 1. Introduction As the photovoltaic market is growing rapidly based on improvements in photovoltaic (PV) modules, manufacturing advances, economies of scale and cost reduction [1], reliability, failures, and their associated energy losses, more questions are beginning to be asked. According to the project report, Technical Risks in PV Projects [2], failures can be categorised into components (modules, inverters, mounting structure, connection and distribution boxes, cabling, potential equalization and grounding, lightning and protection system, weather station, communication and monitoring, transformer station, infrastructure and environmental influence, storage system, and miscellaneous) and phases (product testing, photovoltaic (PV) plant planning/development, installation/transportation, operation/maintenance, and decommissioning) of the value chain of a PV project. During the operation/maintenance phase, failures can be found in the PV array such as snail trail [3], hot spot, diode failure, EVA discoloration, glass breakage, delamination with breaks in the ribbons and solder bonds [4], light induced degradation [5], low irradiance losses [6], potential induced degradation [7], shading effect [8], soiling effect [9], sun tracking system misalignments [10], wiring losses [11], mismatching effect in solar array [12], and other failures such as ground faults, line-to-line faults, and arc faults; although there have not been many such failures, a recent fire suggests the need for improvements to avoid them [13]. Energies 2018, 11, 363; doi:10.3390/en11020363 www.mdpi.com/journal/energies