Influence of the flow rate and the tank stratification degree on the performances of a solar flat-plate collector

Using a thermal model of finite differences, the performances of a solar flat-plate thermal collector wholly manufactured in a copolymer material is studied in low flow conditions. The influences of the flow rate and the stratification of the tank are analysed. Thermal performances, productivity and efficiency of such a solar system (collector with surface of 2 m(2) and a storage tank of 150 litres) are presented for a Mediterranean site. Such a system presents a yearly mean efficiency of about 55.5% and 53.0% and the annual mean of daily productivities are 4.98 kWh and 4.75 kWh for, respectively, high thermal stratified tank and fully mixed tank. These results show that a stratified tank has much higher performances than a fully mixed tank. With high degree of stratification saving energy is higher (5.25% over one year of use) than fully mixed tank. The use of polymer materials reduces the collector weight by 50% in comparison with a traditional metal collector, what implies an easier installation. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.