Pretty much necessary to mix panels...problems...

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Feenix
Feenix Registered Users Posts: 16 ✭
in Off Grid Solar & Battery Systems #1
Hi All!

I just got off of the phone with the Wind and Sun store, since I want to add to my system. I have a 24v/900w totally off-grid system which works really well here in southern AZ. During monsoon season, we get cloudy (obviously), and I had called the store to ask about getting a turbine. It seems (and I already knew this) that my money would honestly be better spent on more PV, since I still charge when it is overcast and in monsoon, we still have full sun until around 11-noon or so before it starts to cloud up.

My question: I have six BP 150w panels which are no longer in production. It is nearly impossible to match these guys up to something, last time I did I had to order them from FL, paid $350 in freight and overpaid for the panels.

I will not be "tossing these out" and getting new ones just so I can add a little more PV to my roof.

That said, when I spoke with the salesman, he suggested I ask my question here. I know it is a standard question: can I mix panels. And I also know the answers are vague and weird. They range from "throw all of your panels away and buy new ones" to "all of my panels are unique, and my roof looks like a quilt."

The panels I am looking at are kyocera 250w, VOC 36.8, IMP 8.39 amp. (http://www.solar-electric.com/solar-panels-mounts-kits-accessories/solarpanels/kyocera-solar-panels/kyocera-kd250gx-lfb-250-watt-polycrystalline-solar-panel.html).

The ones I already have are: BP 150w, VOC 43.5, IMP 4.35 amp (http://www.altestore.com/store/Solar-Panels/150-Watts-Up-Solar-Panels/BP-SX-150B-150W-12V-Solar-Panel/p2694/). These are arranged in two strings of three panels in series.

I know I will lose efficiency. I know that the bigger panels will be wimped down to the smaller ones. Technically this is already happening, since my two strings are at slightly different angles from each other.

So, my questions:

1. Will doing this "hurt" anything?
2. Will doing this be worth it (~$600)
3. Do you have a better idea that doesn't cost that much more? Such as adding a second charge controller?

Thank you SOOOOOO much for your help!
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #2
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    Re: Pretty much necessary to mix panels...problems...

    SO I see nothing about batteries and am assuming your grid tie. Either Micro-inverters or another central inverter are possible.

    If your off grid let us know the balance of your equipment.
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  • Feenix
    Feenix Registered Users Posts: 16 ✭
    #3
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    Re: Pretty much necessary to mix panels...problems...

    Oooops, sorry. Not used to the forum thing. I am off-grid and have 8 L-16 batteries.
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  • Feenix
    Feenix Registered Users Posts: 16 ✭
    #4
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    Re: Pretty much necessary to mix panels...problems...

    Batteries: eight L-16. 24v, 740 AH
    Outback inverter/outback MPPT charge conroller
    Six BP panels: 900w total, two strings of three 150w panels.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
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    Re: Pretty much necessary to mix panels...problems...

    You know what the easiest, most efficient way to mix different panel types is?
    A second charge controller. Cures all ills in one go.

    The Kyocera and the BP panels are quite far apart in both Vmp (never mind Voc; it's not the rating you want for comparing) and Imp.

    If you've got 900 Watts of panel now, what charge controller are they on?
    I would expect about 28 Amps from that array using an MPPT controller on a 24 Volt system.

    Your L16 batteries are at least 300 Amp hours, and eight of them means 600+ Amp hours so you are way under-paneled at the moment.
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  • Feenix
    Feenix Registered Users Posts: 16 ✭
    #6
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    Re: Pretty much necessary to mix panels...problems...

    That's pretty much what I was already thinking, but it is nice to have some confirmation! It looks like charge controllers have gotten a lot cheaper since mine came out, too. Is it a fairly "easy" thing to wire in a second controller to the system? I looked at a few diagrams, and it looks like it would get wired in on the DC breaker side.

    Thanks for your help! And yes, I have 720 AH of battery...so definitely under-paneled. Funny thing is that I have been living in the house for two years and no problems. Technically, still no problems. But my son wants to use his electronic gadgets more and more, especially when it is cloudy! ;)
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
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    Re: Pretty much necessary to mix panels...problems...
    Feenix wrote: »
    That's pretty much what I was already thinking, but it is nice to have some confirmation! It looks like charge controllers have gotten a lot cheaper since mine came out, too. Is it a fairly "easy" thing to wire in a second controller to the system? I looked at a few diagrams, and it looks like it would get wired in on the DC breaker side.

    Two controllers parallel to the battery. Each will have its own breaker/fuse. Do not run two controllers through one!
    Thanks for your help! And yes, I have 720 AH of battery...so definitely under-paneled. Funny thing is that I have been living in the house for two years and no problems. Technically, still no problems. But my son wants to use his electronic gadgets more and more, especially when it is cloudy! ;)

    Are you sure they're in such good shape? Check the SG. It sounds like you have more battery capacity than you need. 720 Amp hours would be 4.3 kW hours on a 24 Volt system @ 25% DOD. Pretty respectable amount of power.

    What we'd normally see for that battery bank: 2244 Watts of array. So you've got room for 1344 more Watts.

    Your OB controller is either 60 or 80 Amp. What I would do here is get a MidNite Kid 30 Amp MPPT controller for the existing panels. Then you can put up to 1800 Watts of new panels on the old controller.

    You may have guessed this is why most people sell their old panels and go with an all-new array.
    With Vmp of 34.5 on the BP's x three in series you have a string Vmp of 103.5.
    Three of the Kyoceras at 29.8 each would be 89.4 per string. That 14 Volt difference is pretty large, so putting them all on one controller is bound to be a power loss. There's no telling exactly what power point the controller would pick, but the high Voltage string can pull the lower one up above its Vmp thus losing current whereas the lower Voltage string can pull the higher down costing power. Probably a 14% power loss over what it could be (with 'equal size' arrays).
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #8
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    Re: Pretty much necessary to mix panels...problems...

    If things are Okay so far, and you live close enough or get to Flagstaff enough to save the shipping you might consider adding these;

    http://www.solar-electric.com/solar-panels-mounts-kits-accessories/solarpanels/hiposopa/topoint-jtm-190-72m-solar-module.html

    They have specs that are close to you panels in VMP, 36.5 volts so you could add them to your system as another string of 3. Having 3 strings you would need to add a combiner box if you don't already have one. I don't think there is tax on solar in Arizona, if you purchase today, you can save 5% getting you close to the $600 make you were looking for and you can make plans to add more to your 'quilt' in the future. This should max out a 60 amp charge controller so future additions would require another charge controller.

    It appears that they must order these, so check to see if additional shipping would apply to in store pickup!

    This would bring you up to about a 8% charge rate, in 'sunny' Arizona this might be all you need, likely what has kept you in business so far!
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • Feenix
    Feenix Registered Users Posts: 16 ✭
    #9
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    Re: Pretty much necessary to mix panels...problems...

    LOL! Exactly! I've always known I was under on PV, but since we get such wicked awesome sun down here, it has let me slide. My batteries are always at a full SOC (except for monsoon season and sometimes winter).

    I think I'm going to go ahead and call the store and see what my options are with either the large panels and a new controller or the 190w. Thanks! And I'll let you know what we decide!
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
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    Re: Pretty much necessary to mix panels...problems...

    Good choice, Photowhit. New panel brand it looks like (haven't seen them listed before).

    Providing the wiring from the controller is up to snuff (why we tell people to do that regardless of how much panel they intend to use) Vmp 36.5 is close enough to 34.5 to not make for significant power loss at all.

    But yes the input side will have to be rewired. Still cheaper than a second controller.

    It's getting harder and harder to match up new to old.
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  • Feenix
    Feenix Registered Users Posts: 16 ✭
    #11
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    Re: Pretty much necessary to mix panels...problems...

    Is it getting harder and harder due to the plethora of "grid-tied" PV out there? Or is it just a move towards larger panels? My original panels are from 2003 or 2004. BP doesn't even make small panels like that anymore.
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  • Feenix
    Feenix Registered Users Posts: 16 ✭
    #12
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    Re: Pretty much necessary to mix panels...problems...

    Oh yeah, and I already have a combiner box in the basement. ;)
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #13
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    Re: Pretty much necessary to mix panels...problems...
    Feenix wrote: »
    Is it getting harder and harder due to the plethora of "grid-tied" PV out there? Or is it just a move towards larger panels? My original panels are from 2003 or 2004. BP doesn't even make small panels like that anymore.

    This is pretty much the case. GT installs outnumber off-grid and drive the industry these days. The panels with Vmp around 30 are best suited for GTI's, so off-grid systems need to use MPPT controllers to make use of them and take advantage of the much lower price per Watt that comes from large-scale production and sales. Sharp has quit making anything under 200 Watts as well.
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #14
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    Re: Pretty much necessary to mix panels...problems...

    What's funny is it's actually getting easier to match up some, as panels are being built so large these days. To make installation costs lower (less wiring and mounts) that I've found a lot of the 270+ watt panels are going back to 72 cells. and some even more!
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #15
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    Re: Pretty much necessary to mix panels...problems...
    Photowhit wrote: »
    What's funny is it's actually getting easier to match up some, as panels are being built so large these days. To make installation costs lower (less wiring and mounts) that I've found a lot of the 270+ watt panels are going back to 72 cells. and some even more!

    I have not noticed this and I was just searching for panels these past few weeks. Majority are still around 30 Vmp from what I saw. The KD320 is 40 Vmp, which is taking it the other way!
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #16
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    Re: Pretty much necessary to mix panels...problems...

    I've been sorta shopping the wholesalers lately, Astronergy 300watt range are all 72 cell, Zebra 280 watt are 72 cell, Suntech 290 watt are 72 cell, Canadian Solar 285-305watt are 72 cell, Trina 280-300watt are 72 cell...

    ...in fact, I only saw 1 or 2 in the 300 watt range that were 60 cell. Looks like currently 60 cells are toping out at 270 watts in general.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #17
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    Re: Pretty much necessary to mix panels...problems...
    Feenix wrote: »
    Oh yeah, and I already have a combiner box in the basement

    Depending on how much input wiring/rewiring you are able or willing to do, I would suggest moving your combiner to the outside of your house.

    The reason is lightning protection. The combiner is a good location to put a lightning arrestor. If lightning strikes, it is wise to divert it to ground OUTSIDE your house, rather than bringing it into your basement.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #18
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    Re: Pretty much necessary to mix panels...problems...
    Photowhit wrote: »
    I've been sorta shopping the wholesalers lately, Astronergy 300watt range are all 72 cell, Zebra 280 watt are 72 cell, Suntech 290 watt are 72 cell, Canadian Solar 285-305watt are 72 cell, Trina 280-300watt are 72 cell...

    ...in fact, I only saw 1 or 2 in the 300 watt range that were 60 cell. Looks like currently 60 cells are toping out at 270 watts in general.

    I'm not terribly surprised by this as when it comes to Watts there's only two ways to get them and when you hit the 300 mark the current is getting pretty high for PV: 300 Watts / 30 Vmp = 10 Imp. Upping the Voltage (by adding cells in series) is sensible: 300 Watts / 40 Vmp = 7.5 Imp.
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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #19
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    Re: Pretty much necessary to mix panels...problems...

    ... And, speaking of 72-cell PVs, there are always these:

    http://www.solar-electric.com/solar-panels-mounts-kits-accessories/solarpanels/solarworld-solar-panels/solarworld-sunmodule-sw-315-monocrystalline-solar-panel.html

    72 cell PVs have been in short supply among my favorite sellers of PV equipment, nice to see SW playing in that game. FWIW, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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