[RE-wrenches] Bird droppings

[gary easton]

Thanks Daniel!

On Monday, July 6, 2015, Daniel Young <dyoung at dovetailsolar.com> wrote:

> Hey Gary,
>
>
>
> Basically the area of the dropping will lower the current of that module
> (and the current of that string if this is a string inverter). The amount
> of current loss will be the % of the dropping area vs the area of the cell
> it landed on. Voltage won’t be affected by things the scale of a few bird
> droppings.
>
>
>
> If this is a string inverter, theoretically if one module on the string
> took a hit, then every other module on the string can take a hit too and
> not really increase the impact, as they are all already current limited by
> the first module to take a hit. The current of that string will just be the
> same as the current from the most affected module in the string. So
> multiple droppings really don’t have a big additive affect.
>
>
>
> Assume all birds drop the same size load (you’re not getting seagulls over
> there so you’re talking starlings, robins, barn swallows, all similar size
> :) once one module in a string is hit, there will not be any further impact
> on production until some module in the string gets 2 hits on the *same
> cell on the same module.* Cells are just a string mounted in a module
> frame. So you could have a module with 5 droppings on it if they were all
> on different cells, and it would do the same as a module with just one
> dropping, if they were all the same size.
>
>
>
> At some point that above example breaks down, because the bypass diodes
> will start to kick in if one cell grouping gets hit too hard.
>
>
>
> As for where on the module….untill you get to the point where bypass
> diodes are kicking in, I don’t think there is a difference. And at what
> point would the diodes kick in, you’d need to get an I-V curve tracer out
> and play around with paintballs or something to help quantify that J
>
>
>
> That’s the way I understand it at least. I have not gone out with my I-V
> tracer and dug into this in detail. It’s just based of the core parallel vs
> series wiring of the typical PV source circuit. I have not seen much impact
> to date from bird droppings on our Solaredge installs so far (the ones I
> KNOW where hit by birdie bombers were so close to those that weren’t that I
> can’t pick them out on the monitoring portal, they just look like typical
> manufacturing variances [all within the +/- x% power tolerances])
>
>
>
> With Regards,
>
>
>
> Daniel Young,
>
> NABCEP Certified PV Installation ProfessionalTM: Cert #031508-90
>
> Lead Systems Designer for:
>
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>
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> *From:* RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org
> <javascript:_e(%7B%7D,'cvml','re-wrenches-bounces at lists.re-wrenches.org');>]
> *On Behalf Of *gary easton
> *Sent:* Monday, July 06, 2015 3:36 PM
> *To:* RE-wrenches
> *Subject:* [RE-wrenches] Bird droppings
>
>
>
> I have a customer with a bit of a bird problem.   The array is ground
> mounted and can be easily cleaned but he is wondering what the impact of
> for instance droppings on one cell.   And how it adds up.   Is there a rule
> of thumb for this? Does it depend where the cell is located in the module?
>
>
>
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