SOLAR-POWERED CAR
Some of you may already know that I constructed a very basic solar-powered toy-sized car for a school science project. I basically retrofitted various parts of store-bought items for my ambitious academic purposes. Yes, it did work (on sunny days), but it was a bit clunky and sometimes it needed a bit of a nudge to overcome the resistance of the rough pavement I tested it on. Here's an actualized rough sketch of my junior high project:
In retrospect, I could have made the following improvements to my homemade solar car:
1) BETTER AERODYNAMICS - Since the drag coefficient of my slightly awkward school project with its protruding solar panels was likely close to 1.0, I should have constructed my own chassis or found one that was much more aerodynamic. A teardrop design that significantly reduces wind / air resistance would have been ideal, but that wouldn't have been completely possible without more flexible solar cells. If I had considerably more time, resources, and engineering know-how back then, my science build could have looked more like this illustrated concept below:
2) DECREASED WEIGHT - Sure, I used lightweight balsa wood for the engine platform & supports of my roughly 9-inch long car, but even so, further reductions in total weight would have been helpful. I could have stripped down the toy car's frame to the absolute essentials and I also could have definitely used a much lighter motor. But back then, I guess I sacrificed the combined weight of the miniature vehicle for the convenience of a powerful motor! And while I was wondering if there was some kind of formula out there that defines a threshold for when a heavy engine starts to become counterproductive, I actually came across the following equation. If you're interested in determining the Power-to-Weight ratio of your own life-size vehicle, you simply need to know the power of the engine (P) and the total weight of the car (W) to perform the division calculation. The higher the number, the better your PWR is. (I'm curious how modern-day electric vehicles would stack up against other cars, considering the fact that sometimes their battery alone weighs more than 1,000 lbs…) Some perform this equation using kilograms (kg) & kilowatts (kW) and others use horsepower (hp) & pounds (lbs). Whichever you use, just be sure not to mix the measuring systems without converting them first!
Not that I know anyone who rigorously calculates PWR before making a car purchase in the real world. Still, whether you're working on a school science project or looking to buy the latest vehicle, it's useful knowing that at some point the overall weight of a car can at times contribute to a degree of decreased efficiency.
3) INCREASED SOLAR PANEL EFFICIENCY - This clearly would have been out of reach for a budding student working on a simple school science project, unless I had the sponsorship & backing of some major manufacturers! (With my still forthcoming update here, I'll provide the formula for this…) But for those interested in further developments of this concept, continue reading…
THE SHOCKLEY-QUEISSER LIMIT - I read the other day that photovoltaic cells have a maximum efficiency of barely around 30%! (In theory, at least. A host of variables contribute to degrees of degraded performance at any given time, so 11-15% is more of a realistic scenario. In some cases, there's even a predicted 0.5% reduction of efficiency for residential solar panels with each passing year.)
In 2018, eepower.com reported on some promising research out of the University of Amsterdam Institute of Physics regarding the theoretical energy conversion limits of solar cells. For those interested in technical jargon, the term is the Shockley-Queisser limit. (Good luck trying to pronounce that correctly!) Dr. Chris de Weerd and Dr. Leyre Gomez, in association with Professor Tom Gregorkiewicz & Professor Yasufumi Fujiwara, had discovered that Perovskite crystals have inherent characteristics that may eventually be used to boost the maximum theoretical efficiency of solar cells to 44%. (And yes, some are even waxing poetic about something called Multijunction PV cells which, although are very costly & difficult to produce, can supposedly reach a performance level of 86%. But that's beyond the scope of this page…) We're even finding that efficiency is not only related to material selection, but also to the form & temperature moderation systems of a solar panel. On August 21, 2023, Adrianna Nine reported on extremetech.com that a solar cell in the shape of a leaf can theoretically increase efficiency by 13.2%. And CBS news reported recently that a city in New Jersey has long since incorporated the concept of using lake water to prevent overheating of their solar panel arrays. While I don't know if the resulting temperature changes in the lake environment would cause unwanted changes to the ecosystem or possibly make it more conducive to the existence of phenomenon like algae blooms, it's an interesting concept to explore.
With all the talk of going green and reducing our dependence on carbon-generating sources, we have to realistically look at the present effectiveness of and cost barriers to using solar energy. I'm all for the use of solar power as long as we do our best to source materials locally. But it's clear we need electrovoltaic panels with considerably better performance levels. Will you be the one to develop a cost-effective and truly efficient solar cell?