Design of a twin capacitive load and its application to the outdoor rating of photovoltaic modules

This paper describes the design of an original twin capacitive load that is able of tracing simultaneously the I–V characteristics of two photovoltaic modules. Besides, an example of the application of this dual system to the outdoor rating of photovoltaic modules is presented, whose results have shown a good degree of repeatability. Copyright © 2013 John Wiley & Sons, Ltd.     

Explanation for the dark I–V curve of III–V concentrator solar cells

The measurement of the dark I–V curve is one of the most straightforward methods for characterizing solar cells. Consequently, an accurate knowledge of its meaning is of high relevance for the comprehension and technological feedback of these devices. In this paper, an explanation of the dark I–V curve for concentrator III–V solar cells is presented using a 3D (three‐dimensional) model in order to provide a proper data fit that provides meaningful physical parameters that are also compatible and coherent with a data fit from illumination curves. The influence on the dark I–V curve of the most significant series resistance components of concentrator solar cells is also analysed concluding that only the vertical component as well as the front contact‐specific resistance can be assessable by means of this characterization method while both emitter and metal sheet resistances cannot be detected. For comparison purposes, the same experimental data have been fitted by means of a traditional two‐diode model showing that, although an accurate dark I–V curve fitting can be achieved, the extracted parameters are unable to reproduce illumination data since lumped models assume the same ohmic losses distribution for both dark and illumination conditions. Copyright © 2007 John Wiley & Sons, Ltd.     

Dark I–V curve measurement of single cells in a photovoltaic module

A simple method of obtaining single cell dark I–V curves in a photovoltaic module was developed. The method does not require disassembling the module and was verified experimentally. From the dark I–V curves, the cell characteristic parameters were obtained. By following the time evolution of the characteristic parameters it is possible to determine the main degradation mechanisms and predict the mean life time of the module before failure. Copyright © 2005 John Wiley & Sons, Ltd.     

A 500‐kW PV generator I–V curve

This paper presents the measurement of the I–V curve of a 500‐kW PV generator by means of an own‐made capacitive load. It is shown that I–V curve analysis can also be applied to big PV generators and that when measuring the operation conditions with reference modules and taking some precautions (especially regarding the operation cell temperature), it is still a useful tool for characterizing them and therefore can be incorporated into maintenance procedures. As far as we know, this is the largest I–V curve measured so far. Copyright © 2013 John Wiley & Sons, Ltd.     

Characterization of the spatial distribution of irradiance and spectrum in concentrating photovoltaic systems and their effect on multi‐junction solar cells

The irradiance and spectral distribution cast on the cell by a concentrating photovoltaic system, typically made up of a primary Fresnel lens and a secondary stage optical element, is dependent on many factors, and these distributions in turn influence the electrical performance of the cell. In this paper, the effect of spatial and spectral non‐uniform irradiance distribution on multi‐junction solar cell performance was analyzed using an integrated approach. Irradiance and spectral distributions were obtained by means of ray‐tracing simulation and by direct imaging at a range of cell‐to‐lens distances. At the same positions, I–V curves were measured and compared in order to evaluate non‐uniformity effects on cell performance. The procedure was applied to three different optical systems comprised a Fresnel lens with a secondary optical element consisting of either a pyramid, a dome, or a bare cell. Copyright © 2011 John Wiley & Sons, Ltd.     

Quantitative evaluation of shunts in solar cells by lock‐in thermography

Infrared lock‐in thermography allows to image shunts very sensitively in all kinds of solar cells and also to measure dark currents flowing in certain regions of the cell quantitatively. After a summary of the physical basis of lock‐in thermography and its practical realization, four types of quantitative measurements are described: local I–V characteristics measured thermally up to a constant factor (LIVT); the quantitative measurement of the current through a local shunt; the evaluation of the influence of shunts on the efficiency of a cell as a function of the illumination intensity; and the mapping of the ideality factor n and the saturation current density J₀ over the whole cell. The investigation of a typical multicrystalline solar cell shows that the shunts are predominantly responsible for deterioration of the low‐light‐level performance of the cell, and that variations of the injection current density related to crystal defects are predominantly determined by variation of J₀ rather than of n. Copyright © 2003 John Wiley & Sons, Ltd.