pv panel array wiring

[redroot]

greetings other power people,

I have an existing mish-mash pv panel array.

3 different models: photowatt, solarex, BP

4 different wattages: 50, 100, 120, 150

All different ages: from 3 years to unknown?

I have 3 different series strings, wired for 24 volts dc,  

all strings currently go into a power distribution block (bdp)

then go to charge controller, batteries, etc....

My questionS>

am I losing pv panel rated output in each string because of mixed performance from mixed panels?

How do I best test for the different output of panels?

If I was to match panels output  and wire those panels that match the best in new strings, how does the bdp effect the total output of the array?

Should I have each string go directly to its own charge controller?

(of course wire cost becomes an issue)

Should I just try to sell these panels and buy all new panels?

( again costs will be the issue here)

Looking for experience with wiring-up a mish-mash of panels for best efficiency.

thanks,

redroot

[Volvo farmer]

Post your specific strings, brands and wattages here and if I'm bored, I'll Google the Vmp for you and tell you if your panela are closely matched or not. Most panels have Isc, Voc and Vmp ratings on the back, so you could give us that information as well if possible.

I know BP bought Solarex and I think the Vmp of the two brands is likely very close on nominal 12V panels.

[redroot]

thanks for the first reply,

I can get the specs off the panels themselves.

mostly I am looking for some guidance on the string/bdp/charge controller wiring possiblities.

the solarex panels are more than likely 10 years old, the BP are 3 years old, they are very different beasts.

look for efficiency,

redroot

[thirteen]

because of the different ages of the panels I would suggest you test each panel. Each panel should have a piont where you hook up the wires. Discontect each panel and test them as cloely togehter at the same time.  As close as possible to get the best resulut. You may have one that has enternal damage that can not be seen. So balanceing the panels with the outputs is the best place to start.

[wooferhound]

In general . . .

when you wire panels in series, the current will be equal to the lowest performing panel, the voltages will add together. Your best series connections for 24 volt should be.

 50w and 100w panels = 100w at 24v losing 50w

 120w and 150w panels = 240w at 24v losing 30w

you have a total of 420w panels at 12v

and a total of 340w panels at 24v because of the mismatch

as others have said, depends on the condition of your panels

and the actual output

[dr2pks]

If you're that bored, do it for me too.  I have 2x80w Matrix poly seconds from AAA Solar in Abq. a 55w BP poly and a 75w BP mono.  None of them say anything on the back.  I know Triple A maintains there should not be more than 5% diff. between mixed panels.  Seems irrelevant to me - especially with indiv. panel diodes.

[ghurd]

There is a reason they are seconds. And why they don't have a sticker.

Series the 2X80W, series the 55&75W. If you want 24V.

That 5% is within many brand's tolerances of 1st quality PVs. Why didn't they put a UL or CE sticker on them?  

Matrix (and others) make warranted PVs of the same size, but rate them from 65 to 90W.  

If the 80W's were good enough to be 80W, why didn't Matrix rate them as 75W, put on the UL/CE sticker, and sell them for more money?

I see A^3 solar still lists 85W Matrix 2nds, without the 25 year warranty. And how they have a waiting list.

Funny?  Matrix went under a while ago. Maybe because they were selling 75W PVs as 80W, but at a discounted price?

I liked the Matrix PVs.  Their business practices (Bernard) left a LOT to be desired. Never had a bad one (USA or France).

Last few times I spoke with Bernard, the skids of PVs were always on the way.

They never got here.

The indiv. panel diodes will make no difference with 12V or 24V systems.  Unless one fails to short, which is very bad.

G-

[dr2pks]

>There is a reason they are seconds. And why they don't have a sticker.

They have small cosmetic faults/chips around the margins of the crystals. The effect on output is negligble.  3A tested them and so did we.  They have no sticker because they also have/had no warranty.

>Series the 2X80W, series the 55&75W. If you want 24V.

Will keep that in mind.

>That 5% is within many brand's tolerances of 1st quality PVs. Why didn't they put a UL or CE sticker on them?

The 5% 3A was talking about was the amount of wattage diff between panels in a mixed array.

>If the 80W's were good enough to be 80W, why didn't Matrix rate them as 75W, put on the UL/CE sticker, and sell them for more money?

The 80s were good enough for 3A to call them 80s.  My tests - while not precise - are close enough for the price paid.  Cosmetic flaws cannot be sold for more money.  People want the unflawed at retail.

>I see A^3 solar still lists 85W Matrix 2nds, without the 25 year warranty. And how they have a waiting list.

The price is right if it's only cosmetic.

>Funny?  Matrix went under a while ago.

I heard they moved the factory to Germany because demand there is so outrageous.

>Maybe because they were selling 75W PVs as 80W, but at a discounted price?

That was 3A's claim.

>I liked the Matrix PVs. Never had a bad one (USA or France).

Never seen a bad one either.

>The indiv. panel diodes will make no difference with 12V or 24V systems.  Unless one fails to short, which is very bad.

Or unless your simple low tech 12vdc crib doesn't have diodes downstream.

So why does 3A say you shouldn't mix panels with too much wattage difference?

[Volvo farmer]

Nice analysis.

I didn't take from his post that he only had the four panels in those specific wattages. I thought there might be pairs of something or another in there. If he only has four panels in those wattages, your analysis is spot-on IMO.

[redroot]

O.k.

to get specific, and hopefully bore lots of you:

my mish-mash of pv panels:

I have 3 photowatt  105 watt vmp 17.3 6 years old

I have 4 solarex msx 60 watt vmp 16.8 age unknown over 10 years

I have 2 solarex msx 120 watt vmp 16.6 3 years old

I have 1 solarex sxu 120 watt vmp 16.8 5 years old

I have 8 arco         50 watt vmp 16.1  age unknown over 10 years

I have 10 solarex     62 watt vmp 17.1 age unknown 10 years old

I understand the voltage matching, and lowest common denominator, I will get up there and test their performance in real time, real sunlight.

My question is still hanging about using a power distribution block.

Lets say I currently have 3 strings, each one having an #8 gauge wire, all 3  going to a pdb, then a 2/0 wire going 80 feet to disconect, then charge controller, and onwards,  what happens to the voltages and perfomance of these 3 strings?  

Do they all drop to the lowest voltage of one particular string, which would be the lowest voltage,  because they all are sharing the same pdb?  

Does it make better since to have each individual string, which is matched with best associated voltages, to have it's own wires, going to it's own charge controller?

still looking for most efficient wiring possibilities for used panels.

redroot

[ghurd]

If a 1A PV and a 3A PV are in series, the output will be about 1A.

The bypass diodes do nothing in a 12V system.  

They are not the same as blocking diodes.

[Volvo farmer]

Several things are confusing here. BP bought Solarex in '01, so your 3 year old Solarex panels are a mystery.

You have about eighty amps there at 24V. There has not been until very recently, a single charge controller on the market that will do 80A@24V, yet you imply that you have a single charge controller, another mystery.

80 feet of 2/0! Perhaps enough copper there in scrap value to get an MX60! I gotta run here and don't have time to figure it out, but that seems like way more copper than you need there. I'm running about 30A, more than 80', with #6. I'll try and post more later.

[ghurd]

Looks easy to me, because almost all are in pairs.

Matched panels go together in strings of 2.

All that is left is a 105W and a 120W. Series those.  A little loss, but it could be a lot worse with 28 mismatched panels.

They will all be operating at the same voltage, slightly higher than the battery voltage, but below the Vmp.

Might want an easy way to regularly test those Arco PVs.

G-