João Paulo N. Torres

Aging of solar PV plants and mitigation of their consequences

Photovoltaic solar fields are planned to operate during many years, so the monitoring of the plant parameters and performances undoubtedly represents an adequate way to ensure a safe and long term operation for the overall system. Values around 10%/year of photovoltaic system degradation in 1991 fall to 12% in 25 years in PV panels using modules manufactured after 2000, mainly due the recent technology advances seen in the field of renewable. Obviously, these results require that system operation should follow an adequate maintenance. In this work, the main failures in the most critical components of conventional PV solar plants are described and ways to mitigate them are recommended, in order to achieve a reduction of unexpected overthrow occurrences. The photos presented were taken in solar PV plants located in Portugal.

Validation of a Simulation Model for Analysis of Shading Effects on Photovoltaic Panels

Numerical simulation results and modeling on the electrical features of concentrating photovoltaic-thermal (PVT) using the free circuit simulation package from linear technology corporation (LTSPIC ...

Stationary solar concentrating photovoltaic-thermal collector — Cell string layout

The aim of this work is to design the cell string layout in stationary concentrating photovoltaic (PV) or hybrid systems (PVT) in order to minimize the effects of both the longitudinal and transversal shading inherent to concentrating collectors. In this paper it is determined the best configuration of a PV string of cells, composed by several modules, by using a simple mathematical model based on the current vs. voltage of the PV cell. The model calculates the power vs. voltage curves of different possible configurations, in order to identify the optimal one according to efficiency and reliability. The company SOLARUS manufactures PVT collectors with cell strings of 38 solar cells connected in series. Solar cells in the concentrated side of the collector are shaded due to the presence of the aluminium frame of the PVT collector. The effects of shading and non-uniform illumination are minimized by including bypass diodes. Each string has 4 modules of bridged cells, each one associated to a bypass diode. In this work, different combinations of string cells in the collector receiver have been simulated using the free circuit simulation package from Linear Technology Corporation (LTSPICE). Test results are provided by SOLARUS to validate the proposed approach. A comparative analysis is presented at the end, showing that the simulation model is an important tool to define the module configurations that achieve the best energy efficiencies of the PVT panel.

Coupling Analysis in Concentric Ring Waveguides

Coupled mode theory in dielectric waveguides has been studied for parallel waveguides and for non-parallel waveguides, among bent and straight optical waveguides between two non-concentric bent waveguides or even between concentric ring waveguides. The last case is treated in this work. Results are compared to those obtained by using the finite element method (FEM). We studied the influence of the curvature radius, the separation distance between the waveguides and the refractive index of the inner waveguide in the energy transfer between waveguides. In particular, the mechanism of energy transfer between concentric waveguides was analyzed.

Effect of Reflector Geometry in the Annual Received Radiation of Low Concentration Photovoltaic Systems

Solar concentrator photovoltaic collectors are able to deliver energy at higher temperatures for the same irradiances, since they are related to smaller areas for which heat losses occur. However, to ensure the system reliability, adequate collector geometry and appropriate choice of the materials used for all their components will be crucial. The present study focuses on the re-design of the C-PV collector reflector currently produced by the Swedish company Solarus AB, together with a comparative analysis based on the annual assessment of the solar irradiance in the collector. An opensource ray tracing code (Soltrace) is used to accomplish the modelling of optical systems in concentrating solar power applications. Symmetric parabolic reflector configurations are seen to improve the PV system performance when compared to the conventional structures currently used by Solarus. The parabolic geometries, using either symmetrically or asymmetrically placed receivers inside the collector, achieve both the performance and cost-effectiveness objectives: for almost the same area or costs, the new proposals for the PV system may be in some cases 70 % more effective as far as energy output is concerned. Index Terms – C -PV solar systems, MaReCo, ray-tracing, reflector design, Soltrace.

Frequency Response Simulation Analysis of Waveguide Photodetectors

In waveguide photodetectors the bandwidth and the quantum efficiency may be specified almost independently because the absorption of light is in the longitudinal direction whereas the current flows in the transversal direction. Then, these devices may combine high bandwidth with high quantum efficiency. In this paper a detailed numerical analysis of the frequency response of waveguide photodetectors is presented. The calculations show that the capacitive effects limit the bandwidth but that by an appropriate choice of a series inductance the maximum bandwidth almost doubles.

Analysis of different C-PVT reflector geometries

One of the main advantages of solar concentrating photovoltaic-thermal collectors (C-PVT) is that these systems are all-in-one module type. For this reason, they are associated to less area and material requirements. Nevertheless, these systems require a more complex analysis in order to improve their performances, since the two types of energy conversion are related to the different demands and their cross effects. In the overall analysis, the collector geometry and the used materials for all their components will be crucial to ensure the system reliability. This study presents preliminary work about re-designing the reflector of C-PVT collectors currently produced in the Swedish SME Solarus Sunpower AB with a comparative analysis on an annual basis of the solar radiation that reaches the collector. For the work accomplished, an open-source advanced object-oriented Monte Carlo ray tracing program (Tonatiuh) is used. For low latitudes, two reflector shapes have been selected since they ensure better performances than the current Solarus reflector. These two new designs achieve both the performance and cost-effectiveness objectives: for the same aperture area and for a thinner box, the collector is 7% to 10% more effective and 18% cheaper.

Analysis of dielectric optical ring slab waveguides with interband absorption

An analytical model for the dependence of the complex dielectric constant on the frequency, electrons and holes concentration and temperature was used in order to introduce an imaginary part, the absorption coefficient, providing changes in the TE mode profile.