ABSTRACT
This paper aims to highlight the use of different heat transfer fluid (HTF) configurations based on vegetable oils in Parabolic Trough Solar Concentrator (PTSC). Rapeseed and jatropha oils as innovative heat transfer materials combined with SiO2 and Al2O3 to obtain six (6) HTF configurations are used in a 1-dimensional PTSC model. The thermophysical properties of the nanofluids are determined from correlations derived from the literature, using Gauss-Seidel method from a numerical code developed in Matlab software. Model validation is obtained. Thermal sensitivity analysis shows that the use of rapeseed increases the thermal efficiency of the PTSC by around 4.21 % compared with jatropha. The use of nanofluids reduces thermal losses within the system due to thermal gradients. For a fixed irradiance and each 1 %-4 % increase in volume fraction, thermal efficiency increases by around 1.96 % when Al2O3/rapeseed is used and by 0.47 % when SiO2/rapeseed is used compared with rapeseed. Similarly, thermal efficiency increases by around 1.98 % when Al2O3/jatropha is used and decreases by around 0.20 % when SiO2/jatropha is used compared with jatropha. However, the positive effects of nanoparticles on thermal conductivity alone are not always sufficient to improve thermal efficiency, and thermal effects on heat capacity should also be considered.
ABSTRACT
To assess the production potential, economic profitability and ecobalance of the photovoltaic/thermal (PV/T) system in Cameroon, different configurations of HTF based on water, vegetable and synthetic oils, coupled with different forms of titanium dioxide (TiO2) are used. A numerical code is written in Matlab. The PV/T model connected in direct contact PV-absorber is validated and a multi-objective optimization of the system is performed. The hourly evolution of PV cell temperature for the six HTF configurations revealed a value below 36 °C with Coton/TiO2. The platelets-and spherical-shaped nanoparticles increase the convection transfer coefficient between the fluids and the tubes. TiO2 showed a higher thermal influence in vegetable and synthetic oils than in water at a volume concentration of 4 %. The cotton/TiO2 configuration showed a 12.08 % improvement in electrical efficiency over conventional PV systems with low exergy efficiency compared to water. Configurations with therminolVP-1/TiO2 are better, with the proposed energy cost reduced to 33 % of the price of electricity in Cameroon. The PV/T-Palm/TiO2 system showed an energy cost of $0.03 with a net present value of $568.45, an emission rate of 7.78 kg, a reversibility index of 1.95, an annual cost of $7.07 and a payback time of 5.97yr. This shows that PV/T systems based on vegetable oils are economical.
