Background car news

The limited energy yield of solar panels

Solar panels on building roofs provide significant amounts of energy, but with cars it is different. The surface area of a car roof is relatively small and the sun does not always shine at the ideal angle. Even under optimal conditions, a solar panel on a car roof can generate only a few hundred watts of power. By comparison, an average electric car has a battery capacity of 50 to 100 kWh and consumes about 15 to 20 kWh per 100 kilometers. This means that a solar panel on a car roof per day provides only a few extra miles of driving range, which is often not enough to have a significant impact.

The efficiency of solar panels on cars

Solar panels are becoming increasingly efficient, but current technology typically achieves efficiencies of 15% to 22%. This means that only a small portion of the solar energy is actually converted into electricity. In addition, solar panels function optimally at a specific angle to the sun. Cars are not always parked in the right direction and often drive in the shade of buildings or trees, further reducing yields.

Cost and weight of solar panels

Another important aspect is cost. High-performance solar panels are expensive and add extra cost to a car. In addition, the car’s electrical system must be modified to utilize solar energy efficiently, further increasing complexity and cost. In addition, solar panels add extra weight, which can detract from the car’s efficiency. Since electric cars are already relatively heavy due to the battery, any additional weight is carefully considered.

Durability and wear

Solar panels on cars would be constantly exposed to vibration, shock and temperature changes. This can shorten the life of the panels, meaning they may need to be replaced more often than those installed on roofs of homes. In addition, dirt, dust and bird droppings can reduce the performance of solar panels, requiring regular cleaning to remain effective.

Car manufacturers experiment with solar power

Despite these challenges, some car manufacturers are experimenting with solar panels on electric cars. The Lightyear One, developed by the Dutch company Lightyear, has a large roof area with integrated solar panels. This concept is designed to provide additional range by harnessing solar energy. It never came to actual mass production. The Toyota Prius Plug-in Hybrid also has an optional solar panel on the roof that can partially recharge the battery when stationary. Hyundai offers a similar option with the Sonata Hybrid – not available in Europe. These examples show that while the technology is developing, it is not yet widely adopted.

Are solar panels on cars the future?

Technological developments are not standing still. More efficient and flexible solar cells that perform better in less ideal conditions are being developed. There are also innovations such as thin-film solar panels and integrated solar cells in body parts. While these developments are promising, the question remains whether they will become cost-effective enough to be widely used in mass-production cars.

For now, rooftop solar panels and charging stations remain much more effective for generating renewable energy for electric cars. Most car owners will benefit more quickly by installing solar panels on their home or garage that allow them to charge their car with solar energy without the limitations of a small car roof.

Solar panels on an EV: a good idea?

Although solar panels on electric cars seem like an attractive idea, the technology is not currently efficient enough to make a major impact on driving range. Limited area, high cost, extra weight and technical challenges make it difficult to effectively harness solar energy on vehicles. Still, manufacturers and researchers continue to work on innovations that may be breakthroughs in the future. Until then, grid charging or rooftop solar panels remain the most practical solution for solar electric driving.

Practical examples

There are some cars on the market that do have solar panels on the roof or have experimented with them. Here are some notable models:

Toyota Prius Plug-in Hybrid (Solar Roof)

Toyota offers an optional solar panel on the roof with the Prius Plug-in Hybrid. This panel can recharge the battery at idle and provides energy for accessories such as the ventilation while driving. Under ideal conditions, the panel can provide several extra miles of driving range daily.

Hyundai Sonata Hybrid (Solar Roof)

The Hyundai Sonata Hybrid, a sedan available in some markets, has an optional solar panel on the roof. Hyundai claims this system can provide about 1,300 km of additional driving range annually in sunny conditions.

Lightyear 0 (and earlier Lightyear One)

The Lightyear 0 was a revolutionary Dutch-made solar car with integrated solar panels covering almost the entire roof and hood. This could provide up to 70 km of additional driving range daily under optimal conditions. Unfortunately, Lightyear went bankrupt, causing production to cease.

Sono Sion (canceled project)

The Sono Sion was an electric car with solar cells in the roof, hood and even the sides. This model aimed to provide up to 34 km of additional daily range using solar energy. However, the project was discontinued in 2023 due to financial problems.

Aptera (not yet in production)

The Aptera is a three-wheeled solar car that is still under development. This vehicle is extremely aerodynamic and light, allowing solar panels to cover a significant portion of its energy needs. The manufacturer claims the Aptera can run for months in sunny areas without recharging.

Interesting project from 2019

Toyota Motor Corporation, NEDO and Sharp Corporation (Sharp) conducted an interesting test in July 2019. The experiment was organized to see if the solar charging system on a car could increase the range and reduce the fuel consumption of electrified vehicles. A prototype based on the 2016 Prius Plug-in Hybrid was used for the test. Sharp developed efficient solar cells specifically for vehicles with an efficiency of 34 percent. Toyota mounted this solar panel on the roof, hood, luggage cover and other body parts of the Prius Plug-in Hybrid. The prototype is fully roadworthy.

Approximately 4.8 times more power

The results were quite promising. Thanks to the new solar panel, the Toyota Prius Plug-in Hybrid’s solar charging system produces about 860 watts of power (measured by Sharp). That’s about 4.8 times more power than a standard Toyota Prius Plug-in Hybrid with Solar Roof. In addition to a more powerful powertrain, the prototype also received a system that charges the battery pack when the Toyota Prius Plug-in Hybrid is driving or parked. This technology increases the range of electrified vehicles while simultaneously reducing fuel consumption.

Test Program

Toyota tested the Prius Plug-in Hybrid under various conditions in Tokyo and other locations. The test results obtained on power and charging systems were used to develop a solar charging system for production cars. Toyota shared a selection of the test results with NEDO and Sharp.

The prototype

The test car was equipped with a solar charging system consisting of several solar cells. These collectively have an efficiency of more than 34%. The shape of the solar charging system, quality, materials used and other factors were set up according to Toyota’s prototype requirements. The solar panel consists of 0.03 mm thick foil. This makes it possible to place the foil on curves and tight spaces. The foil is installed on the roof, hood and luggage cover. The solar charging system generates about 860 watts of power in the prototype.

Future developments

• Tesla has experimented with solar panels on the Model 3 and Cybertruck, but it did not prove cost-effective enough to apply it by default.
• Volkswagen at the ID. Buzz showed a prototype with solar panels, but has not yet put it into production.

Although solar panels on cars are not yet standard, the technology continues to evolve. For now, solar energy remains useful mainly for marginal extra range, but it may become more efficient and more widely applicable in the future. The sun shines absolutely free every day. EVs would do well to take more advantage of that.