Question about adding solar panels.

jangojango Registered Users Posts: 5
Hi, i d like some opinions on whether it would work for me to add panels to my system in the following configuration, and any downsides or possible complications.

I have Mitsubishi panels in 4 strings of 3 X 185 watts using a midnite controller in an off grid system.

VOC 30.6
ISC 8.13
Vmp 24.4
Imp 7.58

Could i add 2 more strings of 3 X 195watt panels

Voc 32.9
ISC 8.15
Vmp 27
Imp 7.2

The matchup on paper should look like this

91.8 / 98.7 VOC
24.39 / 24.45 Isc
73.2 / 81 Vmp
22.74 / 21.6 Imp

Also if anyone could recommend a better match or possibly some Mitsubishi 185's i d be interested.

thanks

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Question about adding solar panels.

    Welcome to the forum.

    Basically you're looking at paralleling strings of Vmp (3 * 24.4) 73.2 with strings of (3 * 27) 81. These are the numbers that matter for parallel connections: the Vmp ratings. You've got a difference of 7.8 Volts there, or just about 10% of the lower Voltage strings. It's not ideal, but it will work.

    Right now you've got twelve 185 Watt panels? That's 2220 Watts. What is the system Voltage? 48 I hope, because that would be 71 Amps on a 24 Volt system or 35 on 48.

    Now you want to add six 195 Watt panels, bringing the total to 3390 Watts which should produce about 54 Amps on 48 Volts. If you tried it on 24 it would be a waste of panels.
  • jangojango Registered Users Posts: 5
    Re: Question about adding solar panels.

    Thanks for the reply, thats good to hear that it will work fairly well.

    yes its a 48v system, I have a 120 foot run on 1/0 awg copper, so not too much extra voltage drop.

    I also found these alternative panels after reading your comment about the vmp, and found these BP sx3195 panels that have the following specs, the vmp is identical , these could be a winner if i can get some at a decent price.

    Peak power (Pmax): 195 watts
    Voltage at Pmax (Vmpp): 24.4 V
    Current at Pmax (Impp): 7.69 A
    Open circuit voltage (Voc): 30.7 V
    Short circuit current (Isc): 8.6 A
    Maximum series fuse rating: 15 A
    Operating module temperature: -40C to +85C
    Maximum system voltage: 600 V

    I have to run a 3/4 hp well pump for 6 hours a day, so i need a little extra capacity to make it work, i have 4 X 2580 Sunextender batterys and the manual states no input amperage limit so should be good just wire these BP panels in and add another 2 breakers on my PV array combiner, i have 60 amp breakers on the chargecontroller.

    thanks again
  • PhotowhitPhotowhit Solar Expert Posts: 5,324 ✭✭✭✭✭
    Re: Question about adding solar panels.

    Your VMP is low enough that you might find a better match using pairs of true 24volt panels with a VMP of 36-37 I recently saw some inexpensive ones if I figure out where I'll pm you.

    I think BP quit making panels @18 months ago, so be sure your buying new old stock.

    Another possibility, particularly with your long wire run, would to rewire your panels in strings of 4 for a string vmp of 98, you likely could find panels to run in strings of 3 that would match nicely with that! vmp's of 32 aren't uncommon, and you'll drop your line voltage drop.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • jangojango Registered Users Posts: 5
    Re: Question about adding solar panels.

    Thanks for the ideas. I found some New old stock bp panels, the sx 3195 for 1$ a watt within driving distance, so i grabbed them they also match visually which is always nice. Strings of 4 might be annoying to rewire, as i have 2 racks of 6 panels separated by about 30' c-c. and i ll be getting another one. I wondered if i could do a string of 6 with the midnite controller to get the amps down , but id need the 200 model and i paid for the 150 new just 6 months ago. I can also take some voltage drop as i have 350 watts(summer, more in winter) hydro that keeps my batteries fairly well topped up, the solar is to run pumps and other large cooling loads.

    I have also been playing around with the idea of an Ac coupled off grid system to get my efficiencies up, and (maybe) extend the battery life. Right now i m on 1 inverter 3048fx and after 6 years its not enough anymore, had a couple overheats in the last week for first time so i m going to have to get more inverter power. It was tempting to get a sunnyboy 3000 watt and run pumping direct, but i m thinking i probably need either another 240 autotransformer, or another fx to make that work, its probably cheapest to get a new vfx 3648 as my master inverter and do the Outback setup with a psx240. Probably the aerovironment controller would have been the best way, but too late now.

    Thanks for the help, much appreciated.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Question about adding solar panels.
    jango wrote: »
    I have also been playing around with the idea of an Ac coupled off grid system to get my efficiencies up, and (maybe) extend the battery life. Right now i m on 1 inverter 3048fx and after 6 years its not enough anymore, had a couple overheats in the last week for first time so i m going to have to get more inverter power. It was tempting to get a sunnyboy 3000 watt and run pumping direct, but i m thinking i probably need either another 240 autotransformer, or another fx to make that work, its probably cheapest to get a new vfx 3648 as my master inverter and do the Outback setup with a psx240. Probably the aerovironment controller would have been the best way, but too late now.

    Thanks for the help, much appreciated.

    A couple of quick observations.
    Outback's FX inverters aren't designed for AC coupling. It isn't worth the hassle trying to get them to work this way.
    Likewise, if you want to stack two FX's they should be identical units. In other words your existing FX3048 should have another FX3048 connected to it, not a VFX3648.

    A Sunny Boy is a standard GTI. It isn't going to run anything without a 60 Hz signal to sink to. It will not "run pumping direct". Tossing in a autotransformer will not change this.
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