Is it possible to realize a solar car that runs on 100% sunlight?

With the goal of reducing CO2 emissions to zero, the trend toward electrification of automobile power sources is accelerating worldwide. However, electric vehicles can only emit zero CO2 if they use electricity from renewable sources. In that case, I think there are more than a few people who have thought that it would be better to improve the efficiency of the solar panel and mount it on the roof of the car. So this time, I would like to think about its feasibility.

First, let's find out how much energy there is in the sun. According to data from the Agency for Natural Resources and Energy, the amount of solar energy that reaches the earth's surface is approximately 1 kW per square meter (1 kW/m^2) under ideal conditions.

Next, let's calculate the area of ​​the solar panel that can be installed in the car. Assume that the size of the car is 4.7m long x 1.8m wide. The shape of the body is assumed to be a wagon type with a large roof area. The body of the car is narrowed down toward the front, back, and top, and solar panels cannot be attached to the windshield, so the usable area is 4.7 x 1.8 x 0.6 = 5 m, assuming 60% of the simple flat area. ^2 now. In other words, the maximum amount of energy that can be obtained from the area where solar panels can be installed is 5 kW (approximately 6.8 horsepower).

Moreover, the conversion efficiency of solar panels is currently about 20% (the theoretical limit for crystalline silicon systems is said to be 29%). Therefore, the amount of power that can actually be obtained is no more than 1 kW (approximately 1.36 horsepower). The car can't run like this.

Even if you think qualitatively, it would be a problem if the power drops when you enter a tunnel or shade, and if you can't use it at night, it won't be practical. In that case, it is essential to install a secondary battery (battery that can be recharged and used repeatedly). In fact, even the vehicles participating in the solar car race are equipped with lead-acid batteries and lithium-ion batteries. It is a big point that determines victory or defeat.

By the way, it is essential to install a secondary battery, and the energy obtained from sunlight is only 1 kW in an ideal state. ) and run on the charged electricity seems more rational.

Solar panels can be installed in a much larger area than a car if you use the roof of your home. The average output of solar panels that can be installed in a typical home is about 4.5 kW, so if the time to obtain full output is 4 hours, 18 kWh of power can be obtained. An EV with an electricity consumption of 7km/kWh can run 126km, so it seems absurd to go out of your way to install solar panels on the roof of your car.

However, this assumes that the car is always at home during the day. For example, if you use it for commuting, it will be in the company's parking lot during business hours, so you can not charge it from the solar panel installed at home (install a storage battery at home to store it, or use a grid It is also conceivable to use the system in such a way that it is flexible within the company and the car is obtained from another place at night when the car is at home, but that is not considered in this paper.)

On the other hand, even if you only get 1 kW of electricity from the solar panels you have installed, you can still get 4 kWh of electricity if you have 4 hours of effective sunshine. An EV with an electricity consumption of 7km/kWh can run 28km, so it is enough to cover one-way commuting.

The question seems to be whether you see this as a lot or a little, and whether the cost-effectiveness is reasonable. Even if it was 14 km, it will be 5110 km in 365 days. If this level is reached, there is a possibility that some users will be able to cover all driving with sunlight, so it can be said that we have realized a "solar car that can run only with the solar panel installed in the car". Isn't it?

By the way, in the solar charging system that Toyota has already put into practical use in the Prius PHV, it is said that a 180W solar panel can provide electricity equivalent to driving an average of 2.2km to 2.8km per day (calculation method is linked) ). Further evolving this, Sharp's solar panels, which have achieved a conversion efficiency of 34%, are placed on the top of the body, and a demonstration experiment of a test vehicle that has increased the power generation amount to about 860W will be conducted from July 2019 for about half a year. (Experimental results are unpublished).

Because the power generation capacity is about 4.8 times, the average driving distance that can be obtained in a day reaches about 10.6 to 13.4 km. If it is 12.0km with an interval, it will be 4380km in 365 days. At this point, it seems like a very attractive number, but it seems that the point is whether the cost can be reduced to a level that can be used as a commercial vehicle.