Great! Source? NREL redbook? RE: Number of EC-110's in Series? [RE-w [RE-wre

[Brad Bassett]

I've lived in Olympia for over 30 years now with an eye to the weather, 
and find the following; The NREL red book gives the daily minimum low at 
just under freezing. We get quite a bit lower than that every winter 
(except one or two) and can easily be much lower than that in the middle 
of the day. Some will argue that it's OK to use this number because if 
the modules have sun on them they will be warmer. John indicated that it 
doesn't take as much sun to come up to voltage as to warm the modules so 
I think it's probably agree that it's not a low enough temperature to 
use. 

The record low temp in the NREL book is -8 deg F which has only been 
seen on very rare occasions just before dawn (I remember the day - I was 
on Mt St Helens) and then warming up considerable before the sun would 
even have a chance to get onto the solar modules. It would certainly be 
safe to use this number, but if you do, you will have trouble sizing an 
array at all to meet the specs for some inverters (not SMA's which have 
a good v range). 

The number I prefer to use is from the ASHRAE handbook for heating 
system sizing. I think this is what most heating people and architects 
use. It gives a design low temp, which for Olympia is 10 deg F., right 
where I had pegged it on my own (though we haven't seen that low a temp 
for many years now - global warming?). It's conceivable that an array 
here could actually see sunlight at that temperature, but I can't recall 
any time in the past 30 years where it's likely that a solar array would 
have seen sun at a lower temperature. So if the ASHRAE tables are as 
good for other locations as for here I think it would be the right 
figures to use, and it's certainly defensible to approving (or 
dis-approving) agencies.

Brad



> 
> -----Original Message-----
> From: John Berdner [mailto:jberdner at sma-america.com] 
> Sent: Monday, June 09, 2003 1:08 PM
> To: RE-wrenches at topica.com 
> Subject: Re: Number of EC-110's in Series? [RE-wrenches]
>
> 2) I suggest using the historical low to calculate max Voc.  Remember
> we are talking about 30 plus year system life.  You can see full Voc
> long before the modules have enough sun to heat them.

 

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