Headerphoto by Jerome Wassenaar
Today is Wisdom Wednesday! The day where we enlighten you a little more on the technical aspects of our project and how we challenge the future of sustainable mobility with these technological innovations. Electrical engineer Rob will explain everything about the solar panel and the difference between silicon and gallium arsenide (GaAs) solar cells.
Income versus expenses
The solar array is only as good as the car it is on. Designing the best possible solar array takes a lot of cooperation between both the aerodynamics team and the electrical team. Designing just a bare solar array is rather simple: have as many of the cells facing the sun as directly as possible. In essence this would just be a plane with the solar cells mounted to them that is always perpendicular to the direction of the sun. However a car with a large flat plane on top is not very aerodynamic as one might imagine, therefore the top of the car is not flat but bent. Which of course does not help with the performance of the solar array. These are trade-offs between the solar income and the expenses in the form of air resistance.
Getting to the best design
Finding the best balance possible between the income and expenses is a hard task that requires a lot of iterations. First the aerodynamics team will design a model of a car, especially the top part is important in this case. Next the electronics team will design a solar array that would fit on the solar car. Then both the aerodynamicist and the electrical engineer will calculate the performance of the designed car. And finally they will discuss the results and determine points to improve upon. The car might be able to get a little smaller as the solar array uses less area than expected, or the angle of the cells can be adjusted slightly to be more optimal for the sun in Australia. This iteration process can take many weeks as finding the optimal design is all about getting all the little details right. The array should barely fit on the car and be positioned on the spots where the most sun will hit without sacrificing aerodynamic performance.
Gathering the energy
Solar cells are based on so called bandgaps. Bandgaps are created by having two types of for example silicon very close together. When light hits such a bandgap electrons get excited to a higher energy level before falling back down and delivering current. A bandgap is very specific for certain wavelengths of light meaning it does not simply work for all wavelengths that light from the sun consists of. Silicon cells have just a single band gap. However GaAs cells are multijunction cells. Meaning they have multiple stacked layers of different materials forming different bandgaps. They are structured in such a way that each layer gathers energy from different wavelengths and passes on the other wavelengths to the next layers. This way more wavelengths are gathered by the cell thus being able to deliver more energy. This is what explains the large difference in performance between regular silicon cells and multijunction GaAs solar cells.
Wisdom Wednesday recap:
– Designing of the solar panel requires design trade-offs between the solar income and the expenses in the form of air resistance
– Solar cells are based on bandgaps
– Silicon cells have just a single band gap, while GaAs cells are multijunction cells
– Multijunction cells have multiple stacked layers forming different bandgaps