[RE-wrenches] Building strings of modules with variable voltages?

[Daniel Tittmann]

In the rough and tumble world of off grid system management for people who
have been piecing together systems for years it is not uncommon for our
company to come to a project and find many different types of solar
modules.  In most cases these modules are working fine and producing power
but often have different output profiles.   In an effort to upgrade systems
and increase production I have often had the idea of building string of
these different modules and feeding them into an MPPT controller.

Can anyone out there explain if this would be a good idea or a bad one?

Let say we have
4 x 100 watt 17.5 Vmp modules
2 x 245 watt 30.5 Vmp modules

what would be the outcome of 2 strings of modules
both with: 2 x 100 watt + 1 x 245 watt
would this cause issues with the MPPT controller (say OB FM60) or the
modules? Obviously you need to build strings that will fit the profile of
the controller and not over to the series string rating and voltage
tolerance of the modules but from a production standpoint where does this
land?

thanks for your advice
Cheers-
Daniel



Daniel Tittmann
CTO
Greenwired
www.greenwired.com
daniel at greenwired.com
707-923-2001 (office)
707-206-5088 (Cell)
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