Thermal effect of VIPV modules in refrigerated trucks

Abstract

The integration of Photovoltaic (PV) modules within the outer structure of commercial transporters offers a great potential as an additional source of energy that can be utilized, for example, directly by the drive train of the vehicle, or by accessory equipment. However, to understand the benefits of such a system, the effect and relevance of some thermodynamic variables introduced by the Vehicle Integrated Photovoltaic (VIPV) system must be assessed. Particularly, the share of the solar irradiance that cannot be converted into electricity by the solar cell and is instead transformed into heat must be considered for certain applications such as the transportation of goods that require a controlled temperature. A one-dimensional thermal simulation model based on a Resistance-Capacitance methodology was created and validated experimentally. The model was used to predict the thermal behavior of the box-body of a truck for a representative year in three cities in Europe (Stockholm, Freiburg, and Seville), with a known Bill of Materials (BOM), and a set of given assumptions and constraints. It was found that, under the simulated conditions laid in this study, the additional heat generated by the PV modules that manages to go through the insulation material and reach the refrigerated cargo area, may raise the temperature of the contained air by an average of 0.36 °C, 0.5 °C, and 0.67 °C, respectively for the observed cities, and as much as 3.12 °C, 2.98 °C and 2.61 °C. When forced convection caused by the movement of the truck was applied into the model (with a constant wind speed of 50 km/h), the temperature of the solar cell dropped significantly, which, for the case of Freiburg, meant an increase in the contained air temperature of a maximum of 0.6 °C. A refrigeration system was subsequently considered for a target air temperature of 2 °C and −18 °C, and it was found that for the simulated scenarios, the harvested solar energy could easily offset the additional energetic demand caused by the PV system, and, in most cases, completely balance out the total annual demand of the chiller.