| Work Detail |
The German institute Fraunhofer ISE investigated the thermal effects and net energy gains of a 3.2 kW vehicle-integrated photovoltaic (VIPV) system installed on a freight truck with a refrigerated cargo storage area. It was found that, with battery storage, the system could potentially meet the entire energy needs of the refrigeration unit throughout the year in some cases.
The Fraunhofer Institute for Solar Energy Systems ISE (Fraunhofer ISE) in Germany has investigated the thermal effect and net energy gains of a 3.2 kW vehicle-integrated photovoltaic (VIPV) system on a refrigerated truck with cargo storage box and found that the solar energy generated easily offsets the additional energy demand caused by the PV system itself and balances the total annual demand of the vehicles refrigerator.
“Although an increase in the energy demand of the refrigeration unit is expected, it was somewhat surprising to see how easily solar energy compensates for this increase and remains extremely favorable in terms of energy balance,” corresponding author of the research, Luis Eduardo Alanis, told pv magazine .
In the study “ Thermal effect of VIPV modules in refrigerated trucks ”, published in Solar energy materials and solar cells , the research team based their analysis on the assumption that the VIPV system would increase the energy demand of the refrigeration unit and that headwinds would have a cooling effect on the PV array.
The team modelled several scenarios to make an informed assessment of the energy balance. “A one-dimensional thermal simulation model based on a Resistance-Capacitance methodology was created and experimentally validated,” the academics explain.
The model took into account several parameters that affect the cooling load of the truck refrigeration unit, such as geolocation, PV module material specification, meteorological data, basic geometry, and forced air convection caused by vehicle motions. It included bill of materials (BOM) data for two module designs, one with foam and plywood insulation layers for refrigerated applications, and one with foam layers and no plywood for non-refrigerated load applications.
The VIPV module BOM used as the basis for the study was previously developed and validated in a previous Fraunhofer ISE-led project, known as Lade-PV.
The model was used to predict the thermal behaviour of the VIPV system in three European cities: Stockholm (Sweden), Freiburg (Germany) and Seville (Spain). It predicted that for a steady-state case, the air in the refrigerated cargo area could warm up in Stockholm, Freiburg and Seville by 0.36 ºC, 0.5 ºC and 0.67 ºC, respectively, on average over a year, and up to 3.12 ºC, 2.98 ºC and 2.61 ºC as a maximum value, respectively.
The team also modelled the photovoltaic cooling effect of forced convection at a wind speed of 50 km/h. They observed that the temperature of the “solar cell dropped significantly”. In the case of Freiburg, this meant that a maximum air temperature increase of 0.6°C was predicted, compared to the 2.98°C calculated for a stationary scenario.
Noting that the convective heat loss due to the motion of a vehicle with integrated photovoltaic energy is “significant”, the team said that this is a “highly relevant” aspect that must be taken into account when analysing the thermodynamics and performance potential of this type of system. This was demonstrated in two scenarios at 2ºC and -18ºC.
The researchers concluded that although the VIPV adds heat to the system, which affects the energy demand of the cooling unit, the energy obtained from the PV installation is “significantly higher than the increase in cooling demand.” They added that “sufficient battery storage” could allow the PV to meet the energy needs of the cooling unit throughout the year.
The team also stressed that the annual results described in the study are “merely indicative” and that “numerous additional variables” could affect both the energy demand of the cooling unit and the total annual performance of the photovoltaic system.
“A simulation tool can only go so far in understanding a phenomenon with so many variables and that is so complex to model,” Alanis explained. “It would be interesting for us to find the right partners with whom we can take this further and potentially test it in the field under real-life conditions. We may also consider extending the simulation model and considering more influences in the future. For example, the loading and unloading of goods.” |
