Paul wrote:

A question about bypass diodes:

snip

Do most panels have the bypass diodes (to allow current flow through shaded
cells)? The specs for my Shell 100W panels do not mention them. I'm not
talking about the series reverse-current blocking diodes, but the per-cell
bypass. I am considering an MPPT controller, and if the panels have these
diodes, it should be better to connect the panels in series, rather than in
parallel. My installation has three panels, and does have issues with panel
shading. Currently I have the panels in parallel, and use a non-MPPT
controller.

I will probably do some V/I curves for the panels with varying types and
degrees of shading, which should answer the bypass diode question, but until
then any advice would be appreciated.

Thanks,
Paul



IIRC once you are over a fairly low reverse voltage on an individual
cell (I belive somewhere around 5V), if any significant current is
available, long term damage tends to occur. Sources indicate that this
isnt a significant problem in simple 12V battery charging setups but
becomes an issue once the difference between the flat battery voltage
and the array OC output excedes this. Check with the supplier if the
cells are rated for series connection in 24V chaging applications as
they should have shunt diodes or better yet just ask them directly.
Also watch out that you dont exceed the maximum input rating of the MPPT
controller, even in direct normally incident sunlight with additional
light being reflected onto the panels and remember that a supply as low
as 32 volts in a wet envirioment can be a lethal shock hazard.

No doubt Mr G. Ball will be along shortly to point out my mistakes.


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