Research finds: Using on-board photovoltaics can reduce electric vehicle charging time by up to 40%

Electric vehicles with photovoltaic panels installed on the body or roof are expected to achieve a mileage of more than 10,000 kilometers per year when powered by pure solar energy. The payback period for these modules may be as short as three or four years.

TNO tests vehicle-mounted photovoltaic panels (Image source: pv-magazine)

According to foreign media reports, the Netherlands Organization for Applied Scientific Research (TNO) launched a research project on vehicle-integrated photovoltaics, and the above is one of its main preliminary findings. Bonna Newman, the project manager of photovoltaic and travel module technology at the agency, said: "We developed a model to evaluate solar panels installed on electric vehicles to quantify their benefits. We want to see how much photovoltaic power can be generated under different circumstances."

The project involves exploring crystalline silicon, thin film and perovskite technologies. She further explained: “We are testing different technologies to see how they can be used effectively for onboard photovoltaics in a variety of electric vehicles, including buses and trucks.”

benefit

Currently, most electric vehicles on the market still struggle to reach a range of 10,000 kilometers due to the vehicle's energy efficiency. However, Newman said: "The performance of electric vehicles is improving rapidly."

It is estimated that the benefits of on-board photovoltaics are proportional to the level of solar radiation in the region, the demand for electric vehicles, and the price of electricity. She emphasized: "For example, in a place like the Netherlands, there is not much sunshine, but the electricity price is close to 0.2 euros per kilowatt-hour. If we use solar panels to generate electricity instead of the grid, we may directly save 150-200 euros in electricity bills each year. Compared with traditional solar energy, if the solar panels you install on your car are worth about 1,000 euros or 1 euro per watt, there may be a three to four-year payback period."

Compared to electric vehicles that rely entirely on grid electricity, it is estimated that CO2 emissions can be reduced by 250 kg per year. "From an energy transition point of view, this is obviously a big advantage. Of course, this depends on where you are and the type of local grid," she said.

These estimates also include the CO2 from photovoltaic panels based on traditional module manufacturing methods. “We found that in almost all cases, the CO2 benefits of onboard photovoltaics exceed those of pure electric vehicles,” Newman added.

Convenience

Another important factor is the "convenience factor", expressed in terms of solar mileage and the number of times the user has to plug the car into the grid. This remains difficult to quantify for the Dutch research team. "With our most detailed model, we evaluated a Tesla-like car in the Netherlands, which has an average annual mileage of about 13,000 kilometers," she said. "We found that if you install photovoltaic panels on the car, you can drive more than 3,000 kilometers per year using solar energy, reducing the number of charging times by about 25%. In the summer, you can even drive for three months without charging once."

In sunny places like Spain and Italy, charging times could be reduced by around 40 percent per year. “This is possible with current photovoltaic and electric vehicle technology,” said Newmann. “On sunny days, even if the energy source is exhausted, the panels can generate enough electricity to partially charge the vehicle and take it to the nearest charging station without external help.”

Module Integration

When it comes to whether the integrated modules should be manufactured by the automakers or outside parties, Newman said that in the long run, completing the solar module integration within the car factory can allow for better design. "The most practical and cost-effective solution is to complete the photovoltaic system integration within the automotive industry and manufacture it by the automotive OEM responsible for the roof or body parts. Currently, all vehicle-integrated photovoltaic products on the market are completed by the automakers. In addition, after-sales solutions may be a way to promote vehicle photovoltaics faster and better.

As for aftermarket solutions, the way PV is integrated into the vehicle system is slightly different on each vehicle. Therefore, the integrated system needs to be improved or adjusted for the specific vehicle to achieve optimal performance.

In order to integrate the panels into the body parts of the car, TNO scientists hope to use modules that are as similar as possible to traditional products in the solar industry. In this way, a large-scale supply chain can be used to provide improvements, efficiency and costs. Newmann emphasized: "We can bear higher costs than traditional photovoltaics, and if we maintain close contact with the photovoltaic industry in manufacturing, we can get better value in the solar mobility industry."

Crystalline Silicon

In this market segment, the mainstream photovoltaic technology is still crystalline silicon photovoltaics because it has the largest output . Newman pointed out: "At present, we need a higher energy production density than the usual solar thin-film cells (CIGS). We are committed to CIGS integration because it has obvious advantages in terms of light weight and flexibility."

However, the supply chain for crystalline silicon is much better from a cost perspective. “You can bend a crystalline silicon panel into the desired shape. Most parts of the vehicle are flat and can accommodate crystalline silicon. So we think this is the most promising technology at the moment,” she said.

Crystalline solar cells are also easier to bond on car roofs, at least with current leading technologies. Shadows can cross the vehicle in very unpredictable and different ways at different times. In contrast, crystalline silicon also responds better to dynamic shadow environments. "We hope to come up with a thin-film solution in the future that performs better in these environments and eventually add a perovskite layer or a CIGS layer," Newmann said.

Security Question

At the same time, the research team is exploring reliability and safety issues, using crash and split tests to understand what happens when an accident occurs. When an accident occurs, solar panels on the roof or other surfaces may be damaged.

“Normally, for example, one cannot touch the voltage from one corner of the roof to the other and that is not a problem,” Newmann said. “However, in the event of an accident, these parts of the roof could be closer together, potentially endangering rescue workers and a risk of electric shock cannot be ruled out.” The plan is to ensure these panels are at safe levels.

Another important factor is to consider the specific situation when a car with solar panels on the front hits a pedestrian. "For example, we have to see how the glass breaks in a collision with a person's head. We have to see what kind of damage this kind of collision causes to the pedestrian's head compared to a car without panels, and we have to make sure that the use of solar panels does not increase any risks," said Newmann.

She stressed that in this market segment, it is very important to avoid such problems at an early stage. "Even if the technology has clear advantages, we have to make sure we introduce it to the market in a safe way."

Market size

From a technical point of view, there will not be much of a hurdle in introducing 21% energy-efficient panels on electric vehicle bodies and producing tens of thousands of vehicles in the next five years. Many people may consider buying photovoltaic integrated electric vehicles because of the convenience. Newman predicts : "By 2030, electric vehicles equipped with solar panels may account for 10% of the electric vehicle market. This will be a fairly large market."

Looking to the future, Newman said it might be difficult to see electric cars powered entirely by solar panels. “It’s going to be hard to get rid of cables completely,” she concluded. “But if you live in a sunny place, you could drive your car for weeks in the summer without having to charge it.”