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

[Exeltech]

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



--------------------------------------------
On Mon, 9/30/13, William Miller <william at millersolar.com> wrote:

Subject: Re: [RE-wrenches] Using legacy modules on micro-inverters
To: "'RE-wrenches'" <re-wrenches at lists.re-wrenches.org>
Date: Monday, September 30, 2013, 2:24 PM
 
Nick:
What is the upper voltage limit for the M250?  What happens when that voltage is exceeded?

I am trying to use Siemens SP75 modules (two in series) and Shell SQ-150-PC. Below are the specs.  Note that two SP75s in series, if you multiply the voltages by two, is identical to the SQ-150 except for the temperature compensation.  I am not sure what to do with the temperature compensation value if I put two SP175s insereis.  Do you know?
  
Our record low is -10 C and average high is 38C.  If I enter the data for the Shell, the calculator shows they are compatible with the M250.  Entering the data for two SP75s using -0.077 for Temp Comp (SP75) the tool says not.  If I use double (-0.154), then the two SP75s are compatible.  What is your determination?

Thanks,
William
  
  
 From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Nick Soleil
 Sent: Monday, September 30, 2013 9:56 AM
 To: RE-wrenches
 Subject: Re: [RE-wrenches] Using legacy modules on micro-inverters

Hi wrenches,The M250 is not limited to 60 cell modules only.  The M250 has an expanded voltage window which will allow for it to be paired with a wider range of modules.  Enphase has an online module
compatibility calculator which can be used for checking a specific pairing in a specific location, at:
 
http://enphase.com/module-compatibility-calculator-m250-update/. 

Keep in mind that many of the high efficiency, higher voltage, 72 cell modules will not be compatible.