The main goal of an efficient solar car is to make the most of the energy that the sun provides for us. To maximise the irradiation input of our only power source, our solar panel will be made of solar cells with the highest possible efficiency to gain as much electricity as possible.
Making the most of what we got
Unlike a common battery, the behavior of solar cells under load cannot easily be described as the series connection of an ideal voltage source and a constant inner resistance. Instead, the behavior of solar cells is completely non-linear, resulting in a number of effects that should be considered during planning. Most importantly, solar cells provide the maximum power at an operating point that depends strongly on the applied irradiation and the temperature of the solar cell. To make sure that the solar cells are always operated at this optimum state, Maximum Power Point Trackers are used. Those power electronics devices are comparable to usual DC-DC converters, but are programmed to always keep the power at the maximum value.
Since the used Maximum Power Point Trackers need a certain minimum voltage on the solar cell side to operate, we need to connect multiple solar cells in series. At this point, the non-linear behavior of the solar cells makes things complicated for us, because even the shading of a single solar cell in the series reduces the usable power at the Maximum Power Point drastically. This can only be overcome by the smart use of bypass diodes, connected parallelly to the shaded solar cells. Since we can't affort to waste the little energy we get from the sun, we need to carefully adjust our wiring to make the most of what we got.
Beating the odds
To design a circuit layout that works best under the expected conditions, we developed a specialised software that simulates the expected irradiation distribution on the curved solar panel and the temperature of the solar cells throughout the day. The software also returns the expected power output of the whole solar panel, using the characteristics, the wiring and the position of the used components. By doing so, it is possible for us to test different circuit and weather scenarios to determine the optimal layout for our solar array manufacturer.
