2022 engineering

The first solar car in the Baltics was powered by Maxeon produced single crystal silicon elements in sunny Morocco

The Solaride team competed in the Solar Challenge Morocco 2021 in November, a competition for solar concept cars. The goal was to test out the first solar car ever constructed in the Baltics region in real life conditions. We gained much needed experience and knowledge from this endeavor, which will help us in our goal of reaching the podium at the Bridgestone Solar Challenge 2023 competition.

This story will focus on the glistening solar panels on the roof of said car. We’ll start off by explaining the groundworks of these solar panels with the help of Kaia Liisa Hakk, who was in charge of the manufacturing process and Andres Nöps, the team leader of the electronics division from our first season. We’ll find out how long the process of turning one solar cell into an actual solar panel is and how preparation is the foundation to any great project.

The Solar Team

The core of the Solar Team. Starting from the front: Tiit Liivik, mentor; Andres Nõps, head of the Electronics Team from our first season; Katrin Kristmann, engineer; Mait Kukk, mentor; Kaia Liisa Hakk, head of the Solar Team. Photo: Tiit Liivik

The solar panels were a joint effort between the Solar Team and many other Solariders. Kaia Liisa Hakk, one of Solaride’s female engineers, was responsible for manufacturing. She managed to get the teams main objective, which was to manufacture functioning solar panels, done in the fastest compared to other teams and their tasks. The Solar Team also received help from fellow engineers as well as marketers, leading to around 10 people being involved in the manufacturing of 5 solar panels.

Preparation is the key to success

In simple terms, a solar panel is a large plate that is made up of tiny solar-powered batteries that produces solar energy and a solar cell, or photovoltaic cell, is an electrical device that converts the energy of light directly into electricity. The car’s roof has 294 single crystal silicon elements acquired from Maxeon that are then equally divided into 5 solar panels.

Installing the solar panels on the roof of the concept car. On the photo: Katriin Kristmann, one of Solaride’s engineers

Solaride found out about Maxeon’s single crystal silicon elements thanks to Lightyear, a Dutch solar car producing giant, whose roots as a company also lead to a student project very similar to ours. Andres Nõps, the head of the Engineering Team from our first season, says that Lightyear’s representatives were the ones to suggest Maxeon’s single crystal silicon elements based on their own experience. This advice was also factually confirmed - when regular elements’ effectiveness was tested, they only clocked out at around 21-22%, but Maxeon’s elements clocked in with percentages of 24.3% and higher. Nõps mentions that the dutch ran their own tests, where they received effectiveness levels of over 25% leading to an obvious choice regarding Maxeon.

Maxeon Solar Technologies is an enterprise that is currently one of the global leaders in solar innovation which operates in more than 100+ countries. Co-operation with a tycoon like Maxeon is a massive morale-boost for us at Solaride. The leader of the solar panel team Kaia Liisa claims that Maxeons single crystal silicon elements are the most effective out of all the options on the market - one element costs 10.25 euros.

Kaia Liisa Hakk, the leader of the solar panel team, soldering silicon elements using a clamp designed by herself

The manufacturing process for the solar panels began in December 2021 and was completed in August of the same year. Let’s have a deeper look into how the construction took place.

The manufacturing of the solar panels

The number of solar panels

The first thing our Solar team had to decide on was the amount of solar panels needed for the project. The choice was made using information from an MPPT, or Maximum Power Point Tracker, which simply put is a converter that changes the electrical current produced by solar panels into energy that can be used by solar batteries.

An agreement was then quickly reached that the optimal amount of solar panels would be five and that the single crystal silicon elements would have to be distributed amongst the panels as equally as possible, so the outgoing current would be even.

The CAD model

Kaia Liisa then took the car’s CAD model and separated the roof from it, so she could create a 3D model of the solar element. After that, she could place the elements on the model’s roof, but as she learned, this is also not as easy, as it might seem.

It’s important to leave some space between the elements. At first they tried to space the elements with 4mm gaps, but eventually it turned out that 3mm gaps were optimal. They couldn’t just let the elements be side by side either, because it was important that every element had enough room to expand and bend, otherwise there could be a risk of the elements coming into contact with each other, which then could have led to a malfunction. Making the gaps wider was also out of the question, because the roof itself has very limited space.

On the left: The original blueprint for the positioning of the elements on the roof of the solar car. On the right: the current positioning

Making of the fastening tool

The clamp or fastening tool, that Solaride’s engineers designed was specifically made with the intention of soldering solar elements together as precisely as possible in the correct position. The construction of the clamp started in December and the manufacturing process took many months, until the final product was ready to use.

The first task in the development of this clamp was, well, the development. Kaia Liisa says that the team had many drafts and ideas, and that the prototype looked completely different from the finished product. During this endeavor Kaia Liisa had her first opportunity ever to design a clamp, this meant that she frequently asked for advice from our engineering mentor Tiit Liivik as well as other Solaride engineers. Her goal was to make a clamp that would not only work for solar elements, but would be useful in the future as well. The base of the clamp was made out of aluminum, as it is a great heat conducting metal.

While testing out the product our team came prepared and thought a few steps ahead, installing resistors on the clamp itself that would release heat if an electrical current was sent through them. This is important, because soldering creates something called thermal shock when it’s being done on the connections of the solar elements- the tin heats up to 250 degrees Celsius but the element itself stays at room temperature. Thermal shock also increases the chance of the element itself fracturing, which is why it was important that the areas which were being soldered were at an equal temperature throught-out the process.

Kaia Liisa says that the final version of the clamp came through a rigorous process of trial and error. After making the base for the prototype clamp, it was understood that something needed changing, but they weren’t quite sure what exactly. They hypothesized for example that the space between the jaws should be wider. Our friends over at INTAR eventually came and helped us out with their laser cutter, thus providing us with a proper base. But our clamp also had to be tested out before we would make the final product.

Testing the solar elements

The elements were tested over at our Solarstone facility in Viljandi, where the solar panels are made. The goal of our testing was to find the optimal approach to soldering.

Kaia Liisa says that Estonia doesn’t possess any of the machines necessary to solder Maxeon produced solar elements according to Maxeon’s own policies and because they are handmade, the possibility for errors was enormous. The team tested different ways how to make connection with other elements between the tin and the element during soldering.

Solaride’s Head of Engineering for the first season Andres Nöps with the solar elements and mentor Mait Kukk in front of the solar panels. 
Photo: Tiit Liivik

They tried many different ways to add flux - they tried putting them in a bath, then they tried using a brush, but eventually they stuck with using a regular pencil. A flux helps hold together the connection between the soldered object and the aforementioned element. Different methods were also used to test the tin alloy, which were just as complicated and nuanced as it was for the flux. They also tried abandoning the idea of adding tin all together, because the connection should in theory contain tin already. For some reason this didn’t work the way they thought it would, so instead they decided to add the tin on both sides of the connector.

The team got together at Viljandi at least once a month, if not more, for the purpose of testing. Getting a feel for the soldering was time consuming and rough to say the least, as they didn’t want to mess up the expensive hardware. This meant that the team used elements that were ten times cheaper or just cheaper Maxeon alternatives to practice soldering.  

Rows of solar elements, all connected by connectors . The elements on the picture are facing backwards, because the connections for Maxeon elements are located on the back. Photo: Tiit Liivik

Testing the lamination materials

It took about 3 months in total to test out the materials for laminating. To make sure what materials worked best for laminating, they used a local solar panel manufacturer’s (Solarstone) elements from nearby Viljandi. One of the more troublesome issues with the lamination was the thin plastic on top, that kept breaking apart. The team still doesn’t know the exact reason why this happened so frequently while testing, hypotheses vary from heat induced expansion to the different properties of the laminating materials themselves.

A special type of transparent film was used for lamination, with a price tag so hefty for one roll, that a local university student could probably pay off a few months of rent with it. The rest of the materials necessary for solar panel building were already present at the factory, so after one and a half years of preparation and rigorous testing, the manufacturing of solar panels could officially begin in June.

Kaia Liisa Hakk: “It bewilders me to this day, that we genuinely managed to solder the solar panels. This process is something that requires extreme precision and I am honestly surprised they actually worked and produced an output necessary for us, as we had 7-8 different people working on this project simultaneously.”

Making of the solar panels

Visits to the Solarstone factory were frequent after the initial testing phase, when the manufacturing of the panels were just beginning, as it was time to finally make a finished product. Our solar panels were made up of five layers: a transparent film on the back, EVA (Ethylene-vinyl acetate) glue, solar elements, more EVA and the frontal transparent film.

Maxeon elements had to be soldered by hand, making the entire process very time consuming. Our team estimated that everything to do with the solar panels eventually equated up to a price tag upwards of 10 000 to 15 000 euros, making this the most expensive part of the whole project.

First step: solder the elements and double-check

Lamination process is on-going. From the left: Tiit Liivik, Andres Nöps, Mait Kukk

Silicon elements must be handled with care - they are easily susceptible to fingerprints and bending and can break if tapped on too heavily. If even one element breaks, it can affect the entire production capacity of an entire panel. During the soldering process the “+” and “-” is marked so that it’s easier to double-check the connections later on. With this kind of work it is also extremely important to check that the elements themselves are functional and that the solar elements all produce power.

The Second step: prepare and cut the necessary materials needed and clean off the glass surface

The layers of a solar panel on a sheet of glass. Photo: Tiit Liivik

The materials are cut with little room for error and expert precision. To make the solar panels, a glass surface is needed. This has to be continually maintained and cleaned from glue residue, because this may harm the solar elements.

Third step: put the elements in their set place, set up a series connection and double-check that everything works

From the left: Armin Mere, Katrin Kristmann and Andres Nöps making their final preparations before sending off the solar panels to be laminated. Photo: Kaia Liisa Hakk

While setting up the elements it is important to remember that they are placed equally apart from each other and that they are placed in the center of the material. While making the series connections it is important to check if the elements that are glued together with EVA aren’t already melted in place before they enter the lamination machine. And as always, you must check if the connection is working before the lamination process begins.

The fourth and final step: check if everything is where it is supposed to be and send it through the laminator

A solar panel entering the laminator for 17 minutes

Before the second layer of EVA and the final layer of transparent film is added, double-check for small pieces of dust or anything else that may ruin the lamination process, only then are the aforementioned layers added to the pile. They then proceed to go into the laminator alongside the solar elements for 17 minutes at 140 degrees Celsius. After that, remove the panel from the laminator and let it cool off. A solar panel has just been born!

The Solar Team is a wonderful example of how preparation and training leads to stunning results. The Solar Panel Team reached its goal - making the solar panels - much earlier than the other teams at Solaride achieved theirs. The Solar Team also provided other solariders with the opportunity and experience of a real manufacturing process, regardless if they had an engineering background.

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