[RE-wrenches] Using legacy modules on micro-inverters

[William Miller]

Dan:

Thanks very much for the detailed analysis.  So the short answer is that a
48 v micro-inverter will be compatible with either module.  I am old school
and like a little more head room than that, especially since we have not
learned yet if inverter damage will occur on overvoltage.  I am anxious to
try the Power One units.  Anyone else tried these yet?

William




-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Exeltech
Sent: Monday, September 30, 2013 6:01 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Using legacy modules on micro-inverters

William,

PV temperature coefficient of voltage is a function of the number of cells
in series.  For 72 cell PV (or two 36-cell PV in series), the coefficient is
2X that of 36 cells.

Two SP75 in series, in an ambient temperature environment of -10C, and
presuming a cell temperature of -10C at reduced light and a low solar
altitude to minimize cell heating, would exhibit nominally 45.4Voc, and
35.6Vmpp respectively.

Two SP75 in series, in an ambient temperature environment of  38C, and
presuming 1000 W/m^2 orthogonal to the PV module at solar noon, would yield
nominally 36.6Voc, and 28.7Vmpp respectively.

Nominal cell temperature under the latter circumstances would be 69.3C,
presuming a rooftop mount, 6-8" above the roof surface, with 1.5 m/s or less
wind speed, and perfectly orthogonal to the sun at solar zenith.


Two SQ150 under the identical cold ambient conditions would exhibit 44.4
Voc, and 34.8Vmpp.

Two SQ150 under the identical hot ambient conditions would exhibit 36.1Voc,
and 28.3Vmpp.

Nominal cell temperature for the SQ150 under the latter circumstances would
be 70.5C, with the same presumptions as above.


Very slight differences exist between two SP75 in series, and one SQ150, but
as you alluded to below, they're close enough to be considered essentially
identical.



Regards,



Dan