Solar panels are too bulky and difficult to install on ordinary electric vehicles without a roof. The area that can be installed is limited and they are only effective in direct sunlight.
For example, if you install it on the roof of a covered car, you can install a 1 meter * 0.65 meter solar panel. A solar panel of such size has a power of 100 W. It can charge 0.7 kWh. one day, and the tricycle can last two days More than ten kilometers.