Hi

I have a small array (2 175 watt panels) to which i want to add 2 more 180 panels. The system is 48 volts so the 2x24 is no problem. The physical distance between where the 180 panels will mount might preclude wiring them together (Sharp leads are about 51"). The 180's wil be separated by the 175's unless i completely dissasemble the array and re-mount everyting.

My question : is there a problem wiring each 175 with one 180 to output 48 volts...done twice? the wire and breaker were oversized with this eventuality in mind when built. By the time power gets to the controller, it doesn't care where it came from, just didn't want to diddle a diode on the panels by accident.

thanks

ralph

not clear on what your asking ...

You can parrallel the 175's and then connect to parrallel 180's ... should work fine.

If you suggesting a pair of 175's parrallel to a single 180, the current output will be limited to the single 180 ..

more info will be needed to give you a better answer

English is my first language, though it sometimes doesn't seem so.

The array has 2x175 watt panels in series now, making 48v 350watts. I want to add 2x180 panels. To avoid removing and re-wiring everything, can i just install a 180 and re-wire with a 175 together, on each end of the array.? The voltage would still be 48v but the output of both 355 watt sub-sets would be parralled to the MX60. There are 8x175 static panels as well.

edit:
Presently 175+175

Proposed 175+180 175+180

or must I 175+175 180+180

thanks

ralph

Either will work ... do what works best for your installation.

When you wire 175+180 , it will just run a tad higher voltage ( maybe 1/2 volt ) since the 180 is limited by the 175 in current so it will run at a slighty higher vmp point

In real world, there is easily 5 watts differnce between the same rated panels ... so again either is fine

wow i just answered this on naws almost identically to what you put here henry. i assumed the 180 had more current than the 175, but in any case the lesser of the 2 pvs currentwise is what you'll basically get.
i guess it was you that i remembered saying about a slight voltage jump in cases like this so i'll give you the credit henry, but i didn't see it here in this thread as it was just posted today. the voltage jump would still be very small and would not make up for the loss it incurred from lowered current making the overall wattage lower.

Sorry, Hitchikers Guide to the Galaxy moment.

Thanks Henry and Neil. You did indeed see the posting on NAWS, i was covering all my bases. There's not as much traffic on the Solar Guppy site as on others, but what is here is Gold.

Now the question will be, how long are the leads and how far can i stretch them . The extension aluminum angle is installed, the holes are drilled, just need to find another body to hold the panels in place while i bolt them down. The wiring is less physically taxing.

I'll let you know how it turns out, maybe next week i'll find that other set of arms.

ralph

Actual Niel, it will makeup for the reduced current, a vmp point is not an exact point but a crest in a V/I curve. The difference of 5 watts is within the "crest" of the vmp knee ( graph )

I've done exensive testing using curve tracers and various panel types .. you would be surpised at just how much variation you can have and get the vmp value ... about 1 volt on a typical "12" volt panel. yeilds the same power ... ie voltage going up/current goes down and vice-versa

The real key here is with single strings or parrallel strings of the same makeup with an mttp controller ( charge or gridtie )

I got the 180 panels attached to the array on either side of the 175 panels and the leads just make it to the junction box midway between them with enough wire to work with. That will mean paralleling the 2x175's and the 2x180's to the combiner box. BTW, earwigs like contained spaces, like combiner boxes...yuck!

Thanks for your input, very much appreciated.

ralph

sounds interesting henry. maybe you could elaborate somewhat on it.
ralph,
earwigs indeed. they do like to hide in places and if memory serves me right they also stay low to the ground. are your pvs mounted low? you can catch some with rolled up newspaper and they hide in it during the day so you have caught a bunch to dispose of. i don't want to advise you to seal up the box as then moisture condensing inside the box may not escape creating problems too. maybe use a fine mesh screening large enough to allow moisture to move freely, but too small to allow the earwigs through.