This is not how I envisioned my time on the team ending.
I joined two and a half years ago at the beginning of my sophomore year – back then we were called Wind Team. We were a lot less organized and a lot less confident. One of my favorite memories was mounting our rudimentary wind turbine – about the diameter of a watermelon – to the roof of an SUV and speeding through an empty Boeing parking lot across the South Park bridge. Jon drove the car, accelerating to the test speed, Alain held the multimeter, constantly reading the output current, and I hastily recorded it into an excel sheet on my school laptop. Then we ran the test again with the speedometer ticking higher.
Now I’m stuck at home, watching lectures on a laptop and unable to experience the traditions of my senior year. I haven’t been into the shop in over two months, and while the chassis is safely stored in our new spacious trailer, it won’t be racing this summer. The 2020 High School Solar Car Challenge has been postponed until the summer of 2021.
I thank you for all of the continued support. All of the work we’ve done since coming home from Dallas last August was in an effort to break our own record. We’ve learned so many lessons from our mentors, supporters, trials and failures.
I’m disappointed that our year of hard work will not culminate in a 4-day endurance race, but I’m also feeling something unexpected – excitement for the future of our program.
I doubt anyone would envy my position of passing the torch of leadership during the global pandemic. There is so much uncertainty on the minds of everyone, myself included, but there are a few certainties that help me stay grounded. One of those is my confidence that after I graduate, this team will have a bright future. I’m convinced of this not just because of our hardworking advisors, resourceful mentors, and dedicated supporters, but most of all, my confidence is in our promising young team members.
In early March, as soon as school closure seemed likely, our team made a strong effort to quickly transport all project materials off campus. Even as the virus spread quicker than anticipated and social distancing guidelines were implemented across the country, preventing in-person collaboration, team members coordinated their needs and began work on important projects. Structural lead Nigel Barnett, proficient in 3D printing, got to work manufacturing PPE At the time of writing this, he has made about 70 masks for healthcare workers.
I’m consistently impressed by the efforts of young members to take initiative and their quick learning of both technical and broader soft skills.
We’re hosting weekly zoom meetings, which have been helpful in our communication and social interaction. We’re working on a lot of important software related projects, most of all, the custom telemetry system.
Last year, we spliced a device called a “cycle analyst” (a commercial digital monitor intended for electric-bike hobbyists) into our car and used it for gathering and storing data. The device did the job, but not without a number of issues and difficulties adapting this proprietary product for our custom electric vehicle.
Our solution this year is to utilize open source software, mostly arduino, to create our own custom data collection and logging system that is not only more tailored to our needs but also more effective.
The gist of this system is an Arduino Mega board that has 4 serial ports. Think of these like USB ports on your computer. The first port receives critical information from the main battery including temperature, voltage, and current for each of the 434 cells soldered together. The second serial port interfaces with a GPS module that provides estimates of distance traveled and total number of laps. The third serial port receives a host of information about our high voltage systems, constantly updating. This includes the current of the motor, speed, throttle and other driving settings, and the status of our supplemental battery system. These serial ports are all sending data in the most efficient way, raw bytes. These data streams are combined into a CSV file and transmitted by the final serial port – a radio transmitter, replacing last year’s cellular signal which dropped critical information whenever a cell tower was too far.
A dedicated computer or laptop will be equipped with a radio receiver tuned in at the correct frequency, and receive all the information near instantaneously from the comfort of an air conditioned building. Another group of team members are working on the computer program that translates the raw CSV file into an organized and accessible format for analysis. All this work is done so that by the time we roll onto the Texas Motor Speedway, we know the best speed to be cruising at based on available sun, battery capacity, and motor power draw.
But between then, our members will be crunching the data from the extensive testing. Last year’s success was owed in part to the hours of driver training and data collection done while driving at the Paccar test track in Mt. Vernon. We look forward to getting the second solar car race-ready.
It’s not all smooth sailing unfortunately. We’ve faced a major hiccup in the last few weeks. The solar array specifically designed for our second vehicle has been detained in U.S. customs after lamination and shipping from China. They have charged us with tariffs and fees greater than the price of the product itself. The team is disappointed that our work is being impeded by bureaucracy, but like engineers always should, we’re finding ways to work through the issues. In the midst of writing this blog post, the solar panel shipment was mysteriously delivered to our temporary workshop in Seattle. We’re grateful, but without any clear answers, our concern for project sustainability is still high.
The solar array for the second car is very different from our first solar array and its construction offers more opportunity than ever before to learn fundamentals of electrical engineering and develop creative solutions that are applicable to the energy needs of the future.
This is no ordinary solar panel, but an experimental design of an array that provides the most efficient power to a lightweight electric vehicle designed by high school students eager to become professional engineers.
As a quick design review: the solar array will be mounted onto the chassis such that it creates one smooth outer body. This contrasts the previous design where the solar array was a separate flat plate above the driver supported by struts. This flat plate increased the frontal area and introduced airflow vortices, both of which contribute to greater aerodynamic drag on the vehicle. Our new design will greatly improve the efficiency of the vehicle by eliminating these sources of drag, enabling greater range and speed.
This design isn’t without its complexities. The greatest design challenge is maintaining optimal power even when the array is partially shaded by the cockpit housing the driver and its supporting canopy. Stringing cells together is necessary to create a high voltage that charges the main battery, but its design inherently fails upon the shading of a single cell. Since cells in series must have a constant current, the current drop induced by shading of one cell brings the entire string to that low level. Even worse, the shaded cell may create negative voltage that dissipates all of the solar energy in a small region, wasting the energy and potential melting the shaded cell. For brevity, I simplified this explanation, If solar panel wiring interests you check out this site.
The solution to this problem are diodes that provide a path for the current to bypass the shaded cell. These are appropriately named bypass diodes. They dramatically reduce the power lost upon the failure or covering of a few cells.
When Alain and I designed the solar panel in December, I learned all about these concepts. Our resulting production order had many cells disconnected such that we could finish the electrical connections and install bypass diodes of our design and liking. This means that even after arrival from the factory, there is significant work required on our part to complete the solar panel. That work is obviously unable to be completed remotely, so it will have to wait until it is safe to do so.
With all the work this entails, why don’t we build the entire array ourselves? It’s something we deliberated on for months last year. Ultimately, the answer comes down to encapsulation.
Encapsulation is the process of protecting the solar cells from moisture, corrosion and the elements. Without proper protection, the thin solar cells would be quickly destroyed before they can provide a return on investment – even a light shower could prove catastrophic. The panels cells that you see on buildings, homes and large factories are typically encapsulated using EVA (hot glue sticks) and glass.
This design is not feasible for any vehicle due to the weight of glass. Precious solar energy would have to be expended on the high rolling resistance caused by the car’s weight. We don’t have energy to spare – efficiency is our game! The solution is to use plastics which are not as tough as glass but a lot lighter.
Encapsulating the array is a complicated process. At the beginning of last year, we decided to investigate the process ourselves. We purchased a batch of silicon cells and attempted to build small arrays for testing purposes. Here are a few photos for your enjoyment.
The first step is arranging the cells in the correct array pattern. These cells are paper-thin, and extremely fragile, handling them repeatedly is guaranteed to create a crack. Cracked cells still work, but their performance is lower and their chance of failure is higher.
Imagine trying to tile your bathroom floor, except that in addition to worrying about keeping everything square and aligned, the tiles would crack from your hand’s coarse touch.
After organizing the cells in the desired pattern, the next step is creating electrical connections. The cells arrived with small metal tabs that could be placed in between them to conduct electricity. We tried soldering the tiny metal contacts of the tabs to the tiny metal contacts on the back of the cells. As you might guess, this proved difficult. The pressure of the soldering iron could crack the cells and the high heat necessary to melt the solder discolored and damaged the cells. With enough trial and error, we got a better success rate, but it still wasn’t perfect.
Next came lamination. We tried the materials we had on hand, even trying the school lamination machine. Our early attempts used an iron (for clothes) to melt the plastic around the cells, but like the soldering iron, the high heat necessary for melting appeared to have negative effects on the fragile solar cells. Our cleanest lamination technique is shown in the second picture above. We created a seal around the plastic and evacuated all the air. Instead of running an iron over the plastic, we used a heat gun to melt it. The difference was clearly visible. The lamination even looked nice – but it was only 3 cells. Our array needed 504 cells!
At that point we asked ourselves could we build a working array? Our process was tedious and inconsistent. Could we have improved it? Certainly, but we weighed our options and chose to send our plans to a manufacturer in China that had decades of experience wiring and laminating custom arrays rather than spending our limited time building subpar solar panels.
When the arrays arrived from China, they weren’t perfect. A few cells were cracked and we needed to reinforce the output leads, but frankly, they were serviceable and provided the necessary solar power for a reasonable price.
The recent issues with our supplier in China have forced us to rethink our process of putting solar panels on the car. I just gave you a host of reasons why producing them in-house is not ideal, but it’s an option that we are reconsidering. Some college solar car teams have an entire sub-team dedicated to the creation of the solar array. I’ll note that these teams typically have higher budgets, greater access to laboratories and advanced machinery but nevertheless, they prove that students can engineer and produce quality custom arrays. We could too.
Fortunately, the solar panel is the only real setback unique to us (the quarantine is affecting everyone). This pandemic may even have a silver lining for our team.
I’ve spent nearly 3 full years on this team, but for the first time, I’m asking myself: where will this team be in 5 years?
The size, rigor, and pure number of subcomponents honestly has left me with my head down, less aware of the changes around me, and I’m sure I’m not the only one – the solar car project leaves little time to spare. It leaves little room to wonder about the impact the team is having on our school, our community, the young engineers on our team – some female, some underrepresented. I’ve had the chance to wonder about the impact our team has on their confidence and sense of accomplishment. It certainly seems that we’ve made a positive impact on all those fronts – I’m proud of the work we’ve done – and I hope it continues to make a positive impact and reaches even more people.
A little breathing room, which I know is a privilege not everyone has, helps me reflect, wonder about the future, and most of all appreciate my experiences on this team – all healthy things for a young aspiring engineer. Thank you everyone for the love and support.