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Mixing up solar panels
By DanB, Section Solar Posted on Fri Jan 28, 2005 at 01:25:44 PM MST
Can mismatched panels be wired in series?

In preparation to install my new wind turbine, I'm working towards changing my system over from 12 Volts to 48. I was pleased to find that pretty good savings can be had by purchasing 'refurbished' Trace inverters. I expect that selling my old SW2512 will cover most of the cost of my new SW 4048 which is nice. The other main expense for now will be batteries, I need 2 more L16's.
The tricky part is the solar panels. Right now I've got 7 'Solarex' 65 watt panels on my 'front' array. They are 12 volt panels, so I figure 4 of those will make a nice string for 48 Volts, but the problem is... I cannot find the very same panel for sale anymore which leaves me with 3 'strays'. The closest I found is a BP solar 65 watt panel, it's almost exactly the same size and looks very similar, so I've ordered one of those - I believe that will solve all the issues with my 'front' solar array.
The biggest problem is my 'back' array. There I have a 'Matrix' 105 watt panel, which can be wired for 12, or 24 Volts. This panel is no longer manufactured - and even if it were, I cannot really afford another panel at this time. I also have 2 old carrizo 'quads' (ugly old browned panels in wooden frames that produce about half of what they ought to for their size). Each 'quad' makes for a 12 volt panel - and between the two I currently get about 6 - 8 Amps into the batteries. My current thought - is wire up the Matrix panel to produce 24 volts, and then wire the 'quads' in series for 24 volts, and put the whole lot in series to make a 48 volt array. Surely it's not an ideal setup... but would there be any harm in giving it a shot? It seems like all the quads together produce similar power to the Matrix panel, so my thinking is it might not be a bad match.

Mixing up solar panels | 11 comments (11 topical)

Re: Mixing up solar panels (3.00 / 0) (#1)
by Shadow on Fri Jan 28, 2005 at 07:09:39 AM MST

I can't help with your answer, But I'm very interested in your 'Refurbished Trace converter' Where can they be found? Do they come with any sort of warranty?. Thanks

Re: Mixing up solar panels (3.00 / 0) (#2)
by DanB on Fri Jan 28, 2005 at 07:47:04 AM MST

I've been watching on ebay and its pretty hard to beat these prices. Im not sure the details of the warrenty - but I've had very good experiences with 'Alternative Energy Store' over the last few years so this seems a fairly good deal.

http://shop.altenergystore.com/itemdesc~ic~XANXSW4048~eq~~Tp~.htm

[ Parent ]

Re: Mixing up solar panels (3.00 / 0) (#3)
by picmacmillan on Fri Jan 28, 2005 at 07:54:11 AM MST

hi dan...what i have learned is that you can take the mismatched ones and put them in parallel and then the rest in series...get your volts up to charge the batteries if a panel creates 15 volts at 3 amps,then if you used two of them you would be getting around 30 volts which will for sure charge the batteries..if it's 48 volt, then however many panels you need to assure you will be charging batteries....after you have enough in parallel i would put the ones that are the same power output in series.. i was told that the panels will be weaker if there is a cell that is weaker than the rest....correct me if i am misinformed.....i also would be interested in a refurbished controller...pickster
http://www.frecklefarmloghomes.com

Re: Mixing up solar panels (3.00 / 0) (#4)
by ghurd on Fri Jan 28, 2005 at 08:19:28 AM MST

I would recommend against it.
They are 2 different technologies with different characteristics and ratings.
One will overpower the other with more amps than it should have. My bet is the loser will burn up, eventually.

There is a chance that the higher current panel would raise in volts and lower in amps, and the lower current panel would lower in volts for the higher amps. Kind of balancing each other out. Still not a great situation, but maybe workable. Maybe for many years.

If there is NO other use for them, maybe they could be a 'back-up'. Wired up 48v with a disconnect switch. If you 'really' need the power for some reason, turn them on only until the batteries get caught up. Turn them on at 60%SOC, and off at 75%SOC, or whatever. That hopefully wouldn't be often, greatly extending how long the one burning up would last. This is what I would do in the same situation.

BTW BP bought Solarex. Your new panel is probably the same model.

G-
Ghurd.info

Re: Mixing up solar panels (3.00 / 0) (#5)
by Flux on Fri Jan 28, 2005 at 08:29:18 AM MST

Dan

As long as you put shunt diodes across each panel to stop back feeding it should work.

As mentioned above the weakest panel in the string will determine the charging current. It's never ideal to mix various sizes but I would give it a go if I had them.

Flux

[ Parent ]

Re: Mixing up solar panels (3.00 / 0) (#6)
by ghurd on Fri Jan 28, 2005 at 08:32:36 AM MST

There won't be any back feeding.
G-
Ghurd.info
[ Parent ]

Re: Mixing up solar panels (3.00 / 0) (#7)
by fishfarm on Fri Jan 28, 2005 at 08:39:04 AM MST

The SW4048 has auxiliary relays that could be used to control such a disconnect.

Another alternative could be to use the different panels to charge different battery sets, then connect the batteries after dark (perhaps using a photoelectric control).

[ Parent ]

Re: Mixing up solar panels (3.00 / 0) (#8)
by richhagen on Fri Jan 28, 2005 at 12:03:55 PM MST

Because different cell types can reach charging voltage at different light levels, it is generally best to avoid mixing when possible. If you have to then try to match the currents of the panels, and the cell technology, ie. monocrystaline, amorphous, ect. In your case, if you match the currents as well as you can with the panels described, I would expect you won't have any problems other than a slight loss in overall power output. Slight differences in voltage characteristics exist in panels of the same type anyway, exaserbated by age, or a cloud, or shade that passes over part of the string. Rich Hagen
'A Joule saved is a Joule made'

Re: Mixing up solar panels (3.00 / 0) (#10)
by veewee77 on Fri Jan 28, 2005 at 01:59:24 PM MST

what I would do is take the ones you have that are all matched to make 48V. Hook them in that way.

Then take the rest and do the best combination you can to get 48V and it seems like your combination would be the best, and hook them in that way.

Make sure you use blocking diodes! But other than that, use what you have. . .

If you get a few more years out of those old ones, good! but I don't think it will hurt much.

The quads you describe are capable of 85W so if you series them with the Matrix 105, you should be able to get somewhere around 150-190 watts. the best way to see how they work together is to get a meter and a big loading resistor. Get out in the sun and wire them the way you described and measure voltage across each set of panels. the two quads in series and the matrix 105 by itself. If the voltages on each set are close, then they will get along ok. If the matrix is low and the quad pair is high, then the matrix is doing all the work. It won't matter if they reach 48V with a heavy load on them, just so that each 'chunk' measures close to the other.

Did any of that make sense?

Doug

Re: Mixing up solar panels (3.00 / 0) (#11)
by Volvo farmer on Sat Jan 29, 2005 at 04:17:13 AM MST

I'm also not going to be much help but wanted to jump on the thread to complain about the constant rotation of manufacturers of these panels. I've had the same problem as Dan. Buy a panel or two, a few years later you want to add more of the same panel and you cannot buy them. Makes it hard for those of us trying to piece together a system.

I wish the size of these panels would become somewhat standardized, like batteries.

Volvo Farmer

Re: Mixing up solar panels (3.00 / 0) (#12)
by SDO on Mon Feb 14, 2005 at 10:42:44 PM MST

How about building your own panels with cells, buy a bunch of cells
at the cost of finished panels, having hopefully more as a result, store
them and then build more panels as you have time and money to finish
your buildout? That way you hopefully depend less on finished product
and more on yourself and maybe less on manufactures that want to
obsolete product or simply go out of business.

---
Super Dave Osbourne, Man of a Million Shunts
"Not that I expect the current administration to do anything about it."
[ Parent ]

Mixing up solar panels | 11 comments (11 topical)

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