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MPPT's are a magic electronic device that at a simple level take the number of watts coming in (volts x amps) and convert it to the optimal voltage for charging your batteries at the corresponding number of amps. There is a small efficiency loss while doing this. On the good MPPT's it is 98-99%.

We have chosen the Brusa Trackers for our car and they worked very well. This decision was based mainly on good feedback about the particular trackers and availability. The Beil trackers had very good reviews but were only just becoming available at the time we needed to buy them and tech support on a new product just probably wasn't going to be as easy to get.

Our eventual choice of number of trackers and kind of trackers was more complicated than we had assumed at first.

We have a 120V DC motor. This means 10 car batteries. To charge 10 car batteries we need approximately 150V DC. The solar array will be approximately 1000W from 600 cells. Each solar cell gives 0.6V which means that we have a total voltage of approximately 360V. 1000W at 150V is approximately 7 Amps which is potentially too much for a single string as it exceeds many of the MPPT power ratings.

If you use multiple down converters you really need a safety margin in there for cells/panels that have been bypassed. You can't down convert a lower voltage. If you have 360V in two strings you have 180V. If you have bad light and a bypassed panel you couldn't guarantee 150V so you may be throwing away a lot of your energy.

If you use an up converter, you have to make sure you don't reach the up converter level. You can do this by limiting the number of cells in a string. The way our car is laid out means that the sensible number of trackers for us is 5. We should get 70-80V on most of those strings.


Brusa - around US$500 each. These are widely used and widely recommended and worked well for us.
BRUSA Elektronik
Erlen 116
CH - 9473 Gams
Phone:  +41 (0)81 750 35 30 
Fax:    +41 (0)81 750 35 39ΚΚ Office
Fax:    +41 (0)81 750 35 36ΚΚ Development 

Beil Notes

Biel - around US$690 each. These are new, and the Biel folks are very well respected and opinion seems to indicate that these will be great. I have no knowledge of the results from WSC2001.
Andrea Vezzini
Industrieelektronik - I3S
Ingenieurschule Biel
Quellgasse 21
2501 Biel-Bienne

Tel: + 41 (0)32 321 63 72
Fax: + 41 (0)32 321 65 72