Researcher tests potential of car rooftop solar

Ljubljana, 14 March - The idea of electric vehicles generating energy from embedded solar cells is gaining momentum as the automotive sector seeks to become more sustainable. Professor Marko Jankovec from the Faculty of Electrical Engineering at the University of Ljubljana has joined the effort by installing a photovoltaic panel on the roof of his car in a bid to devise a system to monitor photovoltaics in vehicles.

Jankovec has attracted quite a few curious looks with his experiment. "I get mixed comments, some people ask me to what how much additional range I get in my electric car, while those who don't know it's an experiment ask me if I've lost my mind," he told STA.

Mounting a PV module on the roof rails is pointless in terms of aerodynamics because the extra drag means the vehicle consumes more energy than the PV module would produce, but this is not the point of Jankovec's experiment, which he designed earlier this year together with colleagues from the faculty's Laboratory for Photovoltaics and Optoelectronics

He simply aims to develop a measuring system suitable for monitoring integrated photovoltaics in mobile systems such as electric cars.

Photovoltaics a key to sustainable living

Photovoltaics, where solar energy is converted into electricity, is one of the fastest growing technologies in the world. Jankovec said it is particularly important in efforts to decarbonise society and live sustainably.

The conversion of light into electricity leaves behind no carbon footprint other than the energy needed to produce and install the system. Unlike other green solutions such as water and wind turbines, PV modules are more accessible, cheaper, and easier to maintain.

"Because of its advantages, it therefore makes sense to put photvoltaics wherever possible, including in electric vehicles, to extend their range," he said.

The experiment monitors characteristics of photovoltaics in vehicles

Jankovec has attached a PV module with additional sensors to the roof rack of his electric car to see how much sunlight he can capture on all sides of the car. The electricity generated from the sun depends strongly on the type of solar cells, their installation and, above all, the operating conditions.

"The aim is to find out what conditions the installed PV module is exposed to, what electronics are needed to keep up with these conditions, and how much energy would be generated by using such systems on a daily basis," he said.

PV systems are mostly installed on the roofs of fixed structures, where conditions are fairly predictable and constant. When they are moved to vehicles, however, the operating conditions change dramatically.

"We have already shown that the amount of solar energy captured changes in a tenth of a second when we are driving or parking under trees. Any disturbance, however small, such as a change of direction, roadside poles and other objects, the shadow of a tree branch in a car park, has a profound effect on the dynamics," he pointed out.

Preliminary measurements carried out over a month have shown that in winter conditions, the module generated around a third to half of the electricity it would ideally have generated if it was installed on the roof of a house.

"At the moment, our system can generate enough energy for a range of one or two kilometres per day in winter. We will continue with the testing and we expect that in the best weather conditions, we will be able to get somewhere between 10 and 20 extra kilometres. This should be enough for a daily ride to work," he said.

Jankovec has presented the results of the experiment at the PVinMotion international conference in Switzerland. Together with the lab's partners and research institutes, the system will be upgraded and offered as a testing platform. They will also jointly apply for EU electromobility funding.

Ljubljana, Faculty of Electrical Engineering at the University of Ljubljana
A Tesla electric car with which Prof. Marko Jankovec carries out an experiment into the development of measurement system for photovoltaics in e-cars.
Photo: Jakob Pintar/STA

PV potentially part of standard trim within a few years

Europe is moving towards decarbonisation and Jankovec believes that photovoltaics will be welcome in every available patch of land. "So why not put it in vehicles too. And not just in cars but also in trucks, planes, buses, trains," he said.

In the automotive industry, there have been attempts to build electric cars with photovoltaics installed over the entire surface, but they have not made a breakthrough in the market due to their high cost. The situation is now different. Thanks to rapid development, photovoltaics has become the cheapest source of electricity.

"We pay only 10% of the price we did 10 years ago. At the same time, it is the most energy-efficient. The electricity we invest in building it pays for itself in just a year, which means that for the next 30 years, which is currently its average lifespan, we get energy without any input," he said.

Photovoltaic technology is already being fitted to some cars as an optional, upmarket feature, but Jankovec predicts that it could soon be part of every car's equipment.

"At the moment, we have systems fitted as standard in cars, for example, character recognition cameras, various safety systems, etc., which a few years ago were only available in premium trim in prestige models. I expect that, in the next 10 years, photovoltaics will appear as standard trim. It will not necessarily only extend the car's range, but it could also be a source of energy to power additional systems in the car," he added.