Multiple Solar Panel String Scenario

different voltages, no good. different voltages in series string and or combiner box are a no no.  assuming same nominal voltage, strings of different amperages in a combiner are okay.  the current is just additive on the busbars for the output wiring.

if you have a specific example, let the cat out of the bag.  As soon as i/we get a free sec, someone will answer.

james - Alt-E staff

hey,

16,5 nominal or 16.5 vmp?  nominal voltage describes the battery bank that you intend to charge (without getting into further detail)

how many cells are in your homebrew modules?  if 36, then you have a 12v module that runs at 16 or 17v.  if around 54, then you have about an 18v nominal module that runs at vmp of 23v or so.

so what if a person purchases modules, and then decides to add more modules later of a different voltage?  hopefully they would think about that before they buy, because that forces them at least to a different charge controller and perhaps a different combiner as well.

james - Alt-E staff

well, no.  if running at 16.5 vmp, and 20 something open circuit then the modules are likely close enough to run to the same charge controller and combine as well.

the issue is that you do not want mixed modules on a pwm controller because higher voltages will blow it up.  anything higher than 28 to 30 will destroy a simple 12v controller.

if you mix module voltages (strings) [or any different modules for that matter] on an mppt controller, the controller will see different IV curves and the max power point tracking will be rendered ineffective.

yes it is a bummer if you try to add to an array and your modules are not around anymore, but i dont see it as big a deal as you do.

as the need to add happens, you add more production. if the same components are around, great, if not you must have a controller to deal with the new solar.  multiple streams feeding the same lake.  no big deal; especially even the most expensive controller is worth less than 200watts.

james - Alt-E staff