Solar cells

[Sean]

Dear solar car people,

how do you support, stick on, and cover/protect your solar cells?

how do you prevent them from becoming too hot?

are there any videos of your team constructing the top of the car?

Thanks

Sean

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[David Snowdon]

Hi Sean!

Good to see that you've found the open solar car mailing list!

I've used a number of encapsulation techniques.

1. Conformal coating over cells glued to a fibreglass shell
2. EVA encapsulation in a vacuum chamber
3. Gochermann.

Gochermann has, by _far_, given us the most reliable, trouble-free experience of any of these techniques. His panels are lightweight, robust, and generate the energy which we expect them to.

Conformal gives a rough aerodynamic surface. It also cuts out parts of the spectrum, which disproportionately reduces your power when using multi-junction cells. We weren't, but our array never produced the power which we expected it to.

We described our EVA encapsulation technique in a 2001 paper at ISES... It's available for download:

http://www.snowdon.id.au/Publications_files/snowdon01curved.pdf

One note of warning. Having encapsulated two solar arrays, and then using Gochermann's services (and Suncat solar are another provider of similar repute), there is absolutely no comparison in terms of the quality achieveable. These companies have been building arrays for solar cars for decades (literally). They've tried lots of different techniques, and they've done the necessary measurements in order to know what does and doesn't work. Moreover, they've had many years, and many attempts to decipher what works. In general, a solar car team will build a single array, and never get a second shot to make it right. In addition, encapsulating solar arrays is hard work! Our last car had 384 cells in it, but the last array I encapsulated had around 4000! Anything you need to do 4000 times is a big job... Like characterising cells, attaching tabs, etc.

We've found that, given a thin laminate, the cells will remain at approximately the ambient air temperature while the car is moving. Once you stop, it's a different story, and the cells heat up substantially. This reduces the efficiency of the cell by approximately 0.3%/degreeC for Sunpower cells -- it's pretty substantial by the time you're at 40C and losing nearly 5% of your power.