Why are solar electric vehicles absent from the roads?

Solar electric cars do exist and the easiest place to see them is the World Solar Challenge, a race that takes place every two years in Australia. Competitors must drive about 3.000 km from Darwin on Australia's north coast to Adelaide on the south coast, using only energy from the Sun. Many of the cars participating in the race look more like vehicles from an amusement park or science fiction movie than they do on the road. That may explain why solar electric vehicles are not an option for daily travel, at least not yet, according to Popular Science.

Although a lot of sunlight reaches Earth during the day, it is scattered as it passes through the atmosphere, so it reaches the ground relatively low. In an average year, after eliminating the effects of different seasons, the energy level from sunlight is about 342 watts/m2, enough to run a standard refrigerator. Cars come in a variety of sizes, but a large car in the US is about 5,5 m long and 1,8 m wide, so it has a surface area of ​​about 9 – 10 m2, and can collect about 3.420 watts, enough to run a refrigerator, dishwasher, and microwave.

Solar farms transmit electricity to cities and towns using millions of solar panels covering thousands of hectares. Some facilities in desert areas use mirrors arranged in rows to concentrate solar energy. But a standard car doesn't have enough surface area to collect much solar energy.

Another problem is that current solar cells are not very efficient at converting sunlight into electricity. Typically, their efficiency is only about 20%, meaning they convert about one-fifth of incoming solar energy into electricity. This means that 1 watts of solar energy reaching a typical vehicle covered with solar panels only provides about 5 watts of electricity for the vehicle to use. Meanwhile, an electric vehicle needs 3.420 watts to run at 684 km/h.

Vehicles participating in the World Solar Challenge are often very large and have designs that maximize surface area. That helps the car collect as much sunlight as possible. With a concept car, this approach is not a problem, but most models have no windows or other space other than the driver's seat.

Another issue is geographical location, daylight hours and weather conditions, all of which affect how much solar energy can be generated. The Earth is tilted on its axis, so not all areas receive the same amount of sunlight at any given time. When the Northern Hemisphere is tilted toward the Sun, the top half of the globe is exposed to more sunlight, whereas the Southern Hemisphere is colder and darker. As the southern half tilts toward the Sun, areas there receive more sunlight than the upper half of the planet.

Areas at the equator receive more sunlight year-round, so nearby areas like Southern California or the Sahara desert have higher solar energy than places closer to the Earth's poles like Alaska. Solar electric vehicles also have difficulty gathering enough sunlight on cloudy or rainy days. Even many giant solar farms have to plan for times when the Sun does not shine. Drivers need to move even at night. For a solar electric vehicle to run after dark, it needs to use excess energy collected during the day and store it in batteries. Solar panels and batteries increase vehicle weight, and heavier vehicles require more electricity to run.

Researchers are looking for ways to design solar electric vehicles that are more suitable for everyday use. They will need to create a solar cell that converts sunlight into energy more efficiently and is suitable for cars. It is also important to create a low-cost system for cars so that the average buyer can afford it.

Currently, the closest option to solar electric vehicles is home-charging electric vehicles or charging stations. Depending on how electricity is produced, some of the energy loaded into these vehicles may come from solar panels, wind turbines, hydroelectricity or other renewable sources.

An Khang (Follow popsci)