In line with the global green-energy craze, a number of automakers around the world are ready to roll out solar-energy cars, whose outlook is still clouded by several major problems, though.

Sono Motors, a German startup, for instance, has unveiled a solar-energy car model, dubbed Sion, covered with 330 PV cells on its roof, hood, and side panels, while Hyundai and its subsidiary Kia have developed car-roof solar-energy systems, scheduled to hit the market in 2019.

The development results from constant cost decline and growing maturity of solar energy, which has prompted many companies to embrace solar energy as source of power for their products. Many automakers have installed solar panels on car roofs as a supplementary power source. There have yet to be a sedan on the market fully powered by solar energy, which will need full coverage of auto body with solar panels, affecting car appearance and function and entailing high cost.

Sion boasts a cruising range of 250 kilometers and is scheduled to hit the market in the second half of 2019, bearing a retail price tag of 16,000 euros (NT$567,000).

In addition to chargeable lithium-ion battery, Toyota's hybrid car Prius has had the option for installing a rooftop 280 W solar panel, capable of increasing cruising range by 6.1 kilometers during sunny weather, a model which, with an extra cost of NT$70,000, is only available in Japan, though.

Hyundai and Kia will launch three solar-energy models, one with a silicon solar-energy rooftop, the second with a translucent solar-energy rooftop, and the third with a lightweight solar-energy system. The company's hybrid models Sonata and Ioniq with be furnished with 1.56 kWh silicon PV cell and a rooftop silicon solar panel, which can replenish the PV cell with up to 60% of power daily. The models will be available in 2019.

The translucent solar-energy rooftop will be applied in traditional fuel-oil cars, double as a skylight and capable of charging a 12 V battery, thereby boosting the car's operating efficiency and cutting carbon emission. The lightweight solar-energy system, still under development, will be applied in electric cars and installed on rooftop and hood.

Major hurdles remain to be overcome before solar energy can become the major source of power for cars. In addition to the low conversion rate of solar energy, cars are often parked in garage or under the shade of trees of other objects, blocking the operation of solar panels.

(First photo courtesy of Hyundai, written by Daisy Chuang)