Field data of soiling energy losses on PV plants are scarce. Furthermore, since dirt type and accumulation vary with the location characteristics (climate, surroundings, etc.), the available data on optical losses are, necessarily, site dependent. This paper presents field measurements of dirt energy losses (dust) and irradiance incidence angle losses along 2005 on a solar-tracking PV plant located south of Navarre (Spain). The paper proposes a method to calcúlate these losses based on the difference between irradiance measured by calibrated cells on several trackers of the PV plant and irradiance calculated from measurements by two pyranometers (one of them incorporating a shadow ring) regularly cleaned. The equivalent optical energy losses of an installation incorporating fixed horizontal modules at the same location have been calculated as well. The effect of dirt on both types of installations will accordingly be compared.

Solar tracking is used in large grid-connected photovoltaic plants to maximise solar radiation collection and, hence, to reduce the cost of delivered electricity. In particular, single vertical axis tracking, also called azimuth tracking, allows for energy gains up to 40%, compared with optimally tilted fully static arrays. This paper examines the theoretical aspects associated with the design of azimuth tracking, taking into account shadowing between different trackers and back-tracking features. Then, the practical design of the trackers installed at the 1Á4 MW Tudela PV plant is presented and discussed. Finally, this tracking alternative is compared with the more conventional fully stationary approach.

When analysing the influence of shade on photovoltaic (PV) systems, the intuitive assumption is that conversion architectures with more inverters, such as string-and module-inverters, will have lower energy losses associated with partial shading of the generators. However, other phenomena which can affect a system's response to shade, for example, the way in which the inverter performs the maximum power point tracking (MPPT), mean that modular configurations are not always the least susceptible to shade effects. We present a case in which the general tendency of many of the currently available commercial inverters to remain in local power maxima results in a string-inverter configuration behaving worse in response to shade than a central-inverter configuration. Experimental data were collected throughout 2005 and 2006 from PV plants in Arguedas and Sesma (Spain). We interpret our observations with theoretical analysis based on the results of simulation experiments.

A number of findings have shown that the test procedures currently available to determine the reliability and durability of photovoltaic (PV) modules are insufficient to detect certain problems. To improve these procedures, ongoing research into the actual performance of the modules in the field is required. However, scientific literature contains but few references to field studies of defective modules. This article studies two different localized heating phenomena affecting the PV modules of two large-scale PV plants in Spain. The first problem relates to weak solder joints whilst the second is due to microcracks on the module cells. For both cases, the cause is identified, and consideration is given with regard to the effect on performance, the potential deterioration over time, and a way to detect the problems identified. The findings contained in this paper will prove to be of considerable interest to maintenance personnel at large-scale PV plants and also to those responsible for setting module quality standards and specifications, and even the PV module manufacturers themselves.

Currently, the know-how and experience concerning the behavior and reliability of large tracking photovoltaic (PV) plants is scarce. Information such as the availability rate is rarely known. Acciona Solar PV plants installed in Navarra (Spain) in the frame of the Spanish utility grid constitute a representative source of information. The scope of this study is to analyze in detail the behavior along 2006 of six of these plants, located in Arguedas (two plants of a rated nominal power of 940 kWp and 2Á1 MWp, respectively), Sesma (1Á12 MWp), Cintruénigo (1Á44 MWp), Rada (1Á78 MWp), and Castejón (2Á64 MWp). In our analysis, the influence of each type of energy loss affecting the plants has been quantified; and the advantages of dedicating human resources to the surveillance and maintenance of a limited number of generators have been stated. Thanks to the work of the operators, the plants registered mean availability rates above 99Á7%.