J.C. Hernández

Lightning and Surge Protection in Photovoltaic Installations

The aim of this paper is to give scientific background and essential assumptions to be introduced into the design of lightning and surge protection in photovoltaic installations (PVIs), with particular emphasis on the aspects of standardization to be covered. For this purpose, the relevant protective measures given in the standards for conventional low-voltage power distribution systems (CLVPDSs) are adapted in part. This revision is required because the peculiar characteristics of PVIs are different from those of CLVPDSs. The resulting protection approach that determines the advisable protective measures by a risk management has been applied to an actual grid-connected PVI (GCPVI), Univer Project. The extra cost of this protection in this PVI (approximately 3.6% of the system cost) is of secondary importance because of the increase of safety and availability. Furthermore, in order to fulfill with this protection, the surge withstand capability (SWC) of PV modules has been investigated as well.

Guidelines for Protection Against Electric Shock in PV Generators

This paper assesses the protection against electric shock in a photovoltaic generator (PVG), the DC side of a PV installation. Within this context, we discuss the applicability of the protection requirements of the International Electrotechnical Commission 60364, the international standard that provides guidelines for wiring in low-voltage (LV) electrical installations. The unique operational characteristics of a PVG, which differ from those of a conventional AC LV system, made it necessary to revise and adapt these requirements. With a view to discovering the effectiveness of electric shock protection in ungrounded PVGs, we carried out both a theoretical and practical study in a real PVG in order to analyze its electrical behavior. As part of our study, the feasibility of applying an ldquoactiverdquo means of protection was experimentally tested in this same PVG.

Case studies on large PV plants: Harmonic distortion, unbalance and their effects

Some case studies on PV systems are reported with reference to harmonic distortion, unbalance and their effects on protection systems. The experiences are related to: i) laboratory experiments made on commercial LV inverters aimed to study their harmonic impact; ii) harmonics produced by an existing PV plant both at lower and higher frequencies; iii) voltage unbalances caused by high penetration of single-phase connected PV sources; and, finally, iv) untimely tripping of protection systems of overhead lines fed by large PV plants.

Photovoltaic in grid-connected buildings, sizing and economic analysis

The aim of this paper is to develop a methodology that allows to know a optimal size of a photovoltaic (PV) generator in a building (dwellings, commercial buildings, etc.). The adopted design criterion is to optimize the profitability and the amortization of PV installations. There is an optimal maximum size for each building, the profitability of the PV installation decreases strongly for sizes higher than the optimal one. This size minimizes the photovoltaic electricity fed into the grid and covers part of the building electricity consumption.

Guidelines for Protection against Overcurrent in Photovoltaic Generators

This paper gives the scientific background and basic premises that should guide the design of overcurrent protection in photovoltaic generators (PVGs). Overcurrent protection first req ...

Optimal Placement and Sizing Procedure for PV Systems on Radial Distribution Systems

This paper presents a methodology for optimal allocation and sizing of photovoltaic grid-connected systems (PVGCSs) in distribution systems. The optimization process is solved by multi-objective optimization approach with methods to evaluate technical and economical impacts. The technical impact is related with the improvement of the feeder voltage stability. This enhancement is evaluated by means of the potential rise of loadability limits. The economical impact is associated with the PV generation profitability and the potential loss reduction on the feeder. The losses and voltage profile evaluation is based on a power flow method for radial networks with the representation of dispersed PV generators. The application results of the proposed methodology are presented for an actual feeder.

Electric Vehicle Charging Stations Feeded by Renewable: PV and Train Regenerative Braking

At present, electric vehicles are charged at home at night when lower off-peak rates could apply. The purpose of this pilot project is to demonstrate the viability of providing renewable power charging services for electric vehicles at railway station parking lots for commuters during the day. The power needed to feed the charging station comes from a photovoltaic system as well as from the regenerative braking of a 25-kV AC railway traction system (RTS) and a 3-kV DC RTS. The design of the proposed DC microgrid for the charging station also involves an energy storage system (ESS) (battery of variable size and supercapacitor) and the connection to a secondary distribution network (SDR). The paper analyses the two most challenging technical issues: (1) the strategy of power management and converter control; (2) the impact of the size of the ESS. Although an increase in the size of ESS benefits the charge from renewable power, this increases the total investment inevitably. The smart strategy developed from power management, based on DC bus sensing, aims at maximizing the usage of available renewable power by mitigating the impact of charging station on the SDR.

Guidelines to requirements for protection against electric shock in PV generators

This paper is focused on the personal safety on the dc side of PV generators. It deals with the adaptation and application in PV generators of proposed protective measures of the international standard IEC 60364. Different operational properties of PV generators in comparison to conventional ac low-voltage systems require this revision.

Power quality assessment of current electrical vehicle charging processes

The penetration of electrical vehicles (EVs) has an impact not only in the presumably increasing electrical demand, but also on power quality (PQ) of low-voltage (LV) radial distribution systems (RDSs), specifically in the harmonic current emission. Thus, it is essential that EV battery charging system designers should be aware of the potential impact of their designs on harmonic emission. Since the effect of charging systems on RDSs is not merely the numerical sum of total harmonic distortion (THD), harmonic phase cancellation may take place, harmonic phase angles should be also investigated. A theoretical background description on harmonics allowed us to perform a suitable campaign of harmonics measurements. Ten sets of measurements were performed on complete charging cycles of two different types of EVs. The results included the statistical characterization of individual harmonic current distortion and phase angle in order to account for randomness during the charging process.

DC current injection into the network from transformerless and LF transformer photovoltaic inverters

The present paper is focused on the study of the DC current injection in the case of photovoltaic (PV) inverters. The source of the leakage current of the transformerless PV inverters is deeply studied among the three most relevant groups that coexist in the market. This study includes measurements of two types of inverters (transformerless and transformer PV inverters) in order to evaluate and compare the behaviour of the injection of the DC current into the grid. According to the assessment of the measurements, the results show that in both cases there is evidence of DC current in the AC grid side, overcoming the limit applied on most of the standards.