Researchers from Germany and the Netherlands installed photovoltaic modules in a light commercial electric vehicle and evaluated its performance and autonomy for four months.
During this period, the EV made daily 45-minute trips from a researcher’s house in the Hannover area, Germany, to the Institute for Solar Energy Research in Hamelin (ISFH). It remained parked there for a few hours and then returned home in the afternoon before being taken to a charging station.
“This work is a continuation of a previous article that presented an analysis of the energy flow from data collected during a single day. Here we present a more detailed and statistically valid analysis over a long period of four months, from April to July 2021,” the scientists stated.
“Attention was paid to the individual components of the system, such as the photovoltaic modules, the MPPT, the low-voltage battery, the DC-DC converter, the high-voltage vehicle traction battery (HV), and the general losses that occur in the system.”
## Performance, efficiency, and autonomy of electric vehicles
The electric vehicle used was the StreetScooter Work L model. The maximum power of the wafer silicon photovoltaic modules M2 was 2,180 W, distributed on the roof (875 W), the rear (215 W), and the left and right sides (545 W).
The roof modules were individually connected to five independent MPPTs, while in the rest of the electric vehicle, every two modules were connected in series to a single MPPT tracker. All MPPTs were linked to the LV battery and the DC-DC converter, which supplied power to the vehicle’s HV battery.
“The front of the vehicle is oriented to the northwest in both places, but at ISFH, the parking is in the morning when the sun rises, and at home, when the sun sets,” the academics explained. “The rear has a similar radiation profile in both parking positions, as the vehicle’s orientation is almost identical. During the driving phase, as the vehicle’s orientation changes continuously with respect to the sun and due to obstruction from surrounding objects, the rear, left, and right sides receive relatively less irradiation.”
According to their measurements, the parking duration was approximately 106.7 and 382.22 hours for ISFH and residential parking, respectively. After the MPPT conversion phase, a combined total of 49.06 kWh was available for ISFH parking and 153.32 kWh for home parking.
Of these, 29.16 kWh (ISFH) and 98.57 kWh (home) charged the LV battery, 19.9 kWh (ISFH) and 54.75 kWh (home) were directly transferred to the DC-DC converter, and 5.96 kWh (ISFH) and 12.92 kWh (home) corresponded to system auxiliary consumption losses.
“The LV side of the DC-DC converter receives 38.73 kWh (ISFH) and 129.18 kWh (home), which are sent to the HV battery. Taking into account losses in the high-voltage battery, the usable energy for traction is 29.65 kWh (ISFH) and 99.74 kWh (home),” added the scientists.
“During the driving phase, the photovoltaic module produced 9.8 kWh of electricity with a conversion efficiency of 18.01%. After the MPPT conversion stage, 8.3 kWh of electricity is available for the following stages, of which 4.3 kWh charge the LV battery and 4 kWh are supplied directly to the DC-DC converter. The final power of the DC-DC converter is 5.5 kWh, which is transferred to the vehicle’s HV battery during the driving phase.”
## Study conclusions on solar energy in electric cars
It was found that the overall system efficiency, considering multiple energy conversion stages, battery charge/discharge losses, and auxiliary losses, was 60.44% for ISFH parking, 65.05% for home parking, and 66.26% for trips.
Based on the average consumption per kilometer of all trips and the total photovoltaic energy injected into the battery, the team estimated that solar electricity contributed to 530 km of the electric vehicle’s autonomy during the measured period, representing 30% of the total distance of 1,750 km.
The results were presented in the article “Performance analysis of an onboard photovoltaic system on a light commercial demonstration vehicle in Hannover, Germany,” published in Progress in Photovoltaics.
The study was conducted by scientists from the Institute of Energy, Materials, and Devices – Photovoltaics (IMD-3) in Germany, the Institute for Solar Energy Research in Hamelin (ISFH), and the Eindhoven University of Technology in the Netherlands.
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