Olga de Castro Vilela

Performance of solar systems with non-linear behavior calculated by the utilizability method: application to PV solar pumps

Based on the utilizability method we derived, in the first part of the paper, an analytic expression to calculate the time average of physical quantities non-linearly dependent on collected solar radiation. Results are applied to photovoltaic pumping systems (PVPS). Water flow propelled by various types of pumps, centrifugal or progressive cavity displacement, for example, can be conveniently written as a second degree polynomial of the collected solar radiation. In that case, the long-term time average of relevant physical parameters, like water flow or hydraulic power, can be calculated with a very simple expression. The procedure is validated comparing long-term averages of maximum water volume pumped by a PV system, obtained with the utilizability method, with those found by running a 10-year time series. Comparison is made for several climatic regions in Brazil. Results show very good agreement for every month of the year and all locations, with a maximum deviation of 1.7%. The method applied to calculate long-term averages, maximum water volume for example, can be useful for evaluation and design procedures of photovoltaic pumping equipment.

Exact solutions for multilayer optical structures. Application to PV modules

The analysis of multilayer optical devices is important in solar technology as they can be found in a large variety of equipment, particularly in photovoltaic modules. Absorbed and transmitted light by a set of thick layers are usually obtained by ray tracing procedures. When the optical structure is formed by more than one layer, the calculation of both the absorbed and transmitted light is rather complex due to multiple interactions between the several interfaces of the optical device. This paper describes a general analytic procedure, valid for any number of layers, to calculate the absorbed and transmitted light, e.g. solar radiation, through a set of thick optical layers. Consideration of incoming and outgoing light fluxes at each interface, and the assumption that the last interface acts as a light sink, leads to a closed system of equations that can be solved sequentially. Results are applied to analyze the optical behavior of an encapsulated solar cell and a photovoltaic module.

Reverse osmosis desalination: Modeling and experiment

An analytic model for the performance of reverse osmosis desalination systems is derived. Predictions are shown to agree well with extensive measurements conducted on a commercial multistage reverse osmosis desalination unit over a broad range of operating conditions. The model allows a transparent understanding of the dependence of system performance on key design and operating variables. Identifying the characteristic flow rate and length scale of reverse osmosis systems allows a universal description of the variation of the permeate flow rate and recovery factor with the salinity, flow rate, and pressure of the feedwater.

Exact analytic flux distributions for two-dimensional solar concentrators.

A new approach for representing and evaluating the flux density distribution on the absorbers of two-dimensional imaging solar concentrators is presented. The formalism accommodates any realistic solar radiance and concentrator optical error distribution. The solutions obviate the need for raytracing, and are physically transparent. Examples illustrating the methods versatility are presented for parabolic trough mirrors with both planar and tubular absorbers, Fresnel reflectors with tubular absorbers, and V-trough mirrors with planar absorbers.