Soiling and other optical losses in solar-tracking PV plants in Navarra

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 calculate 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

A coupled optical-thermal-electrical model to predict the performance of hybrid PV/T-CCPC roof-top systems

A crossed compound parabolic concentrator (CCPC) is applied into a photovoltaic/thermal (PV/T) hybrid solar collector, i.e. concentrating PV/T (CPV/T) collector, to develop new hybrid roof-top CPV/T systems. However, to optimise the system configuration and operational parameters as well as to predict their performances, a coupled optical, thermal and electrical model is essential. We establish this model by integrating a number of submodels sourced from literature as well as from our recent work on incidence-dependent optical efficiency, six-parameter electrical model and scaling law for outdoor conditions. With the model, electrical performance and cell temperature are predicted on specific days for the roof-top systems installed in Glasgow, Penryn and Jaen. Results obtained by the proposed model reasonably agree with monitored data and it is also clarified that the systems operate under off-optimal operating condition. Long-term electric performance of the CPV/T systems is estimated as well. In addition, effects of transient terms in heat transfer and diffuse solar irradiance on electric energy are identified and discussed

Step-step interactions on the vicinal Ge(001) surface

Ge(001) surfaces misoriented towards the [011] direction have been investigated with a UHV STM. The vicinal Ge(001) surface consists of alternating straight SA steps and rough SB steps. The anisotropie surface stress tensor leads to interactions between the steps, which can be characterised by assigning a force monopole and a force dipole to each step. The monopole-monopole interaction describes the repulsion, the monopole-dipole interaction the attraction between adjacent steps. From STM images the distribution of the step-step separation was extracted. Using this distribution the value of the force monopole and the force dipole has been calculated. It was found that the short range monopole-dipole interaction attracts the SB step towards the lower lying SA step, which results in the formation of DB steps at a miscut angle of 5°

Investigation of the vicinal Ge(001) surface with STM

The morphology of Ge(001) has been investigated with a UHV - Scanning tunneling Microscope. The ge(001) surface was misoriented towards the [011] direction with a miscut angle varying from 0.4 to 5. The surface stress was found to have considerable influence on the step edge configuration as well as the position of the steps with respect to each other

Optical model for multilayer glazing systems: Experimental validation through the analytical prediction of encapsulation-induced variation of PV modules efficiency

A simple analytical calculation based on a transfer matrix method for incoherent optics, allowing the prediction of photovoltaic module efficiencies in different encapsulation conditions is presented. This approach is used for the experimental validation of the main features of the optical model for multilayer glazing systems considered, through the relation between the external quantum efficiency of the module and its optical modeling. The theoretical procedure avoids the need to manufacture and characterize by solar simulator or external quantum efficiency measurements all the variety of photovoltaic module configurations, which is of interest at research and manufacturing levels, especially for building-integrated photovoltaics. The absorptivity of encapsulated solar cells is not directly accessible from direct air-bare cell or airencapsulated cell optical measurements, and therefore analytical or numerical methods are generally needed. The calculations presented in this work provide closed analytical expressions for the layer-bylayer absorption of the different components of a photovoltaic module. From a small set of experimental measurements of a particular encapsulation configuration, and the theoretical expressions for spectral absorptivities, the short-circuit current of a module can be predicted for any other encapsulation scheme. It will be proved that the method accurately matches short-circuit current density of the modules as obtained from experimental measurements. Results will be presented for crystalline silicon and CIGS thin film cell technologies with several glass and encapsulation material combinations.European Commission´s FP