Modeling and assessment of concentrated photovoltaic systems -

Abstract

This research is focused on the modelling of concentrated solar photovoltaic (CSPV) collectors. The PV cells used in the CSPV collectors are known as multi-junction (MJ) cells that can reach efficiencies of about 40percent and work under a radiation of multiple-suns obtained through concentrators. The current-voltage (I-V) characteristics of the MJ cells are very similar to those of flat PV panels and are significantly dependent on their operating temperature. However, the calculation of their operating temperature is involved and there is no accepted and simple formula for such calculation. In this work, a heat transfer problem is solved to determine the operating temperature of CSPV collectors. The MJ cells are lined up in the focal region of a parabolic concentrator and the electric power produced by the cells, the heat lost to the atmosphere by radiation and convection, and the heat transmitted to the cooling fluid are equated to the solar energy rate falling on these cells. The solution of this energy balance equation helps determine the cell temperature. Many parameters are varied to evaluate their effects on the system, temperature and energy wise. It was shown that the electrical efficiency of the MJ cells is improved when there is lower radiation, lower ambient temperature and inlet fluid temperature, higher wind speed, and higher fluid mass flow rate. The receiver has been studied as one control volume or divided into several ones. Simulations show that the temperatures of the cells, the receiver and the outlet fluid tend to increase and eventually reach saturation values when more control volumes are added. This same effect is also noticed when many collectors are placed in series. The model is used to demonstrate the operation of a power plant over a year and to compare its performance to that of a flat PV panel plant. The economics of the operation is deduced in the form of cost of energy produced in - kWh and CO2 savings. Although the CSPV plant costs more for the same land area of a PV plant, but it