SPAM: PV Inverters module strings [RE-wrenches]

[Bill Brooks]

Lee,

The voltage varies slightly with low irradiance, but is a much stronger
function of temperature. The code takes worst-case conditions, because it
wants to be absolutely sure the voltage limits cannot be exceeded. A
Professional Engineer, with good field data on a specific module or system
could make the case for allowing more modules in series if they can prove
beyond a reasonable doubt that the 600 Volt limit of high voltage inverters
cannot be exceeded. However, very few people in our industry have the
experience or credentials to make that judgement.

The easiest thing is to use the 690-7 table and apply the 97.5% ASHRAE
coldest design temperature numbers for your area. Those numbers are several
degrees warmer than the all-time coldest temperature, are more reasonable,
and have technical validity. You can find those tables in an ASHRAE manual
in your library, if you don't own one.

Good luck,

Bill.


-----Original Message-----
From: solplex at montana.com [mailto:solplex at montana.com]
Sent: Friday, November 01, 2002 9:21 AM
To: RE-wrenches at topica.com
Subject: SPAM: PV Inverters module strings [RE-wrenches]


Bill Brooks.  For high voltage inverters in cold country the panel
voltage at record lo temp is a big deal.  If panels are oriented 30° for
summer, and winter sun wants 60°, there will be a loss of power in
winter due to angle and orientation, somewhere around 5-10%.  Ok, most
of the loss would be in amperage I pressume, but some of it would be
voltage.  How much?  As the panel lays flatter, is there more voltage
reduction?

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