Solar Array Update

Recently the array team has been working with Alain Chuzel from Suncat Solar regarding the manufacturing of the solar array for our 7th generation vehicle.  Alain Chuzel specializes in non-traditional encapsulation of solar panels.

Solar panels refer to solar cells that are encapsulated (or laminated) to be more robust and durable.  The process is fairly simple, the solar cells are sandwiched between two sheets of EVA – Ethylene-vinyl acetate, a thermoplastic polymer that acts as bonding -agent.  The bottom back sheet is Tedlar and the upper sheet of the panel is glass.  The layers of material along with solar cells are then put into a solar panel laminating machine that heats up the material to allow EVA to melt and cure evenly.  For solar vehicles, glass as the upper layer is too heavy and brittle therefore a thin plastic sheet layer is used instead.  Although Stanford’s solar car team used glass made by corning as their lamination (see link: http://solarcar.stanford.edu/)  One of the perks of solar car design is that you can do what you wish as long as it works.

For our new array, we will be using are 22.5% EFF Sunpower C60 solar cells, one of the highest efficiency mono-crystalline silicon cells currently available on the mass market. We have made the decision because for the 2013 world solar challenge, gallium arsenide cells (around 25-30%EFF) are limited to 3m^2 compared with the 6m^2 allowed for silicon.

After choosing the solar cell, we have been working on solar cell cutting strategy.  You might ask why on earth would you cut solar cells?  The main reasons are

  • Increase packing density (area cell/total area of panel)
  • Increase voltage (voltage becomes higher with more cells)
  • Accommodate curvature of the car

Sun Power solar cells use Maxeon™  technology which places their metal contacts for conducting current is on the back side of the solar cell.  The cutting would need to avoid the metal contacts which look like “fingers” and only dice the silicon itself.

Cell_cutting

 

The team has been “agonizing” over the past weeks over how many times to cut the solar cells. Each geometric option has its pros and cons and we are currently evaluating them using a matrix. Changing the cutting of the solar cell by a few millimeters completely changes how our array system works and its performance.  Some factors to consider include geometry (does it fit?), finance (can we afford more cutting?), suppliers, and etc. How would we synthesize the information into something that is comparable and make an informed decision?  The answer is we don’t know yet and we are exploring ways into quantifying each parameter so we can sort of compare “apples” to “apples”.

In addition to “agonizing” over the cutting of solar cells we’ve also been running simulations in a MAT-lab program to determine how to optimize cell arrangements for the race.  The program works by importing laying virtual solar cells onto a CATIA model and running this model with solar cells on it over the course of the entire race, in algorithms.  The output of the simulation program gives us an approximate of how much power each cell module is producing.  The team then makes comparisons on different arrangements of solar cells and how they affect performance.

Simulation
Picture of Matlab array simulation with solar cells laid on model. Red = high luminosity

 

Lastly, I would like to share my 2 cents on solar car and solar cells:

Solar vehicle design is a very interesting process because it is a project that spans 2 years with many components and involves the integration of different disciplines with many different “right answers” but a very clear objective – to build a team that will make a solar car that can travel 3000km in as short time as possible while adhering to race regulations.  But all of this begins with a group of students sitting around a table talking and doing simple sketches on paper of what the car might look like.   The team trains you to become much more practical and utilitarian by doing whatever it takes to make it “work”.  It gives you a practical side of engineering that is hard to be learned in classrooms.  You are also completely in charge of designing something that doesn’t seek to put a limit but instead allows you to explore ideas and possibility.  The really hard hard work will begin in the coming month as we wind up design and start making the solar car.

I joined the team initially because I was interested in solar energy.  Through the process I have learned some stuff about solar and I’d like to share some of my thoughts on it.    Many people bring up the fact that the energy from the sun hitting the earth each day is enough to provide all of the world’s power for a year.  While this is true but I am no expert so I will not give thoughts on if solar can solve the world energy problem.  But I think where solar and other renewable such as wind, geothermal, can really be utilized is in the context of third world/rural development.  As citizens first world nations – Canada or other developed countries it is very hard for us to imagine modern life without electricity.   We can sometimes take a reliable electrical grid for granted and forget that there are 1.5 billion people on the planet without access to electricity.  Often these countries have a lot of people living in rural areas which makes having electrical grid for all these places difficult.  Take Nepal for example, it’s one of the poorest countries in the world with 84 % of the population living in rural communities.  It is very difficult for the government to extend a national grid to all the communities because it’s very expensive and there needs to be enough demand such as a city.  This is where renewable energy can alleviate some of the problems because they can generate power in small quantities at any location, almost- as long as the sun shines or wind blows.  Renewable such as micro hydro, solar, or wind can generate power for half of the day and store excess energy into a battery.  At night the residents can access this energy and use it for lighting, television, communication, etc.  This can fundamentally alter their lifestyle and free up time for them to pursue education, or other things to improve their life.

My other area of interest is buildings, hence why I am studying Civil Engineering.  I think solar cells can be better integrated into building envelopes.  Having solar panels on rooftops or as building façade can reduce the building’s electricity consumption during the day when electricity is more expensive.   No electricity will be generated at night but the base load of electricity grid means much less expensive electricity.

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  1. Henri Wistin - April 19, 2015 at 8:45 AM

    Hello,

    I really enjoyed reading your article. I am a civil engineering student myself, in Belgium. I’m currently working on a personal project in which I use sunpower maxeon cells too, but on a much smaller scale. Seeing as you have extensive experience in the field, I was hoping you could advise me on a technical issue I am facing:

    I have to cut the maxeon cells in order to reach a final size of 40*80mm, while also reaching a 5V output. I was wondering if beyond cutting the cells along the metallic contacts, you had also tried cutting in the perpendicular direction? If so, were the cells still functionnal and kept the same 0.5 V output?

    I’m looking forward to your reply.

    Best of luck for the project,

    Henri Wistin

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