<span class="highlight">solar</span> <span class="highlight">panel</span> mystery

Submitted: Sunday, Mar 14, 2010 at 13:39

ThreadID: 76847 Views:6364 Replies:4 FollowUps:16

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SmokeyD

Hi again,

Thought I had this problem licked.

I decided to go the way of the new regulator as I mentioned in my last post - only after that didI decide to put a meter across the solar panels terminals just to make sure of the output volatage. When I did, it read a constant 20.5 volts, not the 36 as mentioned on the back panel. Is this indicative of only half the panel working (diode short) or is "Nomadic Navara" correct in his summation...
"FollowupID: 678169 Submitted: Wednesday, Mar 10, 2010 at 13:29
Nomadic Navara posted:
Ed - I know that, however he is charging a 12 V battery (which is also a little more than 12 V most of the time.) However, a 36 V panel is an unusual size. Smokey said "the regulator the correct one for that voltage and panel." As the regulator does not appear to be an MPPT type things are not adding up. It could well be the correct voltage panel, someone has confused the 36 cells with it being a 36 V peak power point panel and calculated the current out by dividing 200 by 36.

Smokey - you could clear this up by providing the manufacturer and full model number of the panel."

Details listed on the back of the panel are -

(Tong Lin) PMW 200 PW

Watts = 200
Voltage = (VWP) 36.0 volts
current = 5.56 amps

I opened the connection box at the back and the terminals are covered in a foam like substance. I have started to carefully remove the foam (with plastic tool) and have uncovered so far 3 large diodes. The chap from Esolar suggests to remove all wiring from the panel terminal block and measure the short circuit current and open circuit volts. If I get same voltage, then I have 100 watt unit only. It could also be a diode short - in which case he suggests to remove both diodes and check them and then the panel current and voltage again. When I get all the covering off, I'll send a photo of the terminal block.

I am not overly confident with the above, so would appreciate some direction and ideas.

Cheers

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Reply By: Notso - Sunday, Mar 14, 2010 at 14:03

Sunday, Mar 14, 2010 at 14:03

Not knowing a whole lot about solar panels, take this with a grain of salt, but is the 36 volts a "No Load" maximum voltage from the panels? When they are loaded up does the voltage drop to the lower figure?

AnswerID: 408773

Follow Up By: SmokeyD - Sunday, Mar 14, 2010 at 14:07

Sunday, Mar 14, 2010 at 14:07

Hi,

This is purely the voltage read across the panel with no load. I placed the panel outside, placed the meter terminals on the panel leads and got a constant 20.5 volts

FollowupID: 678720

Follow Up By: Notso - Sunday, Mar 14, 2010 at 14:21

Sunday, Mar 14, 2010 at 14:21

I've been looking at some specs for solar panels and the only "open Circuit" voltages I can find for 12 volt panels is around 21 or 22 volts, none of em quote anywhere near the 30s

FollowupID: 678722

Follow Up By: Notso - Sunday, Mar 14, 2010 at 14:23

Sunday, Mar 14, 2010 at 14:23

The 12 Volt Shop range.12 volt shop

Click on Solar panels and the specs are all there.

FollowupID: 678723

Follow Up By: Nomadic Navara - Sunday, Mar 14, 2010 at 14:59

Sunday, Mar 14, 2010 at 14:59

A so called 12 V panel has a peak power point of around 17 V (usually a whisker over) and an open cct voltage of over 20 V. This panel will have 36 cells. There has been panels manufactured with 32 cells, way back they were produced in small sizes to float (maintain) flooded batteries without having to use a regulator with them, these days there are larger ones designed to be used with MPPT regulators.

SmokeyD has quoted the info label on the panel stating "Voltage = (VWP) 36.0 volts ." To me this panel has a PPP of 36 V and it is faulty or has been rewired to only give an output to charge a 12 V battery with a simple regulator. Smokey, you can confirm this by counting the number of cells in the panel, there should be 72 of them.

As the junction box has been opened and fiddled with it is probably too late to claim warranty. Smokey will have to persist and see if he can get it working properly.

PeterD
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FollowupID: 678730

Follow Up By: Battery Value Pty Ltd - Sunday, Mar 14, 2010 at 16:01

Sunday, Mar 14, 2010 at 16:01

SmokeyD,

as has been said before, do a cell count first.

Then grab a voltmeter and measure across each of the three diodes in full sun.

If the cell count is 36, then you've got a 12V panel, split in two 6V strings with individual bypass diodes.
In this case your voltmeter should read around 10V across two of the three diodes.

If your cell count is 72, then you've got a 24V panel, split in two 12V strings.....
There should be 20V across each of two diodes.

Due to the fact that you only measure 20V total panel output, it's either a 12V panel, or one diode has shorted out, effectively cutting in half the 40V output voltage.

Another possibility is that your cell count is 108 which would really point to a 36V panel.
In this case, either two of the three bypass diodes are shot, or mounted the wrong way around.
If they're mounted the wrong way around, I'd imagine the voltage across them would be about 0.5 to 1.0V in full sun.
If they've shorted out, then there'd be hardly any voltage across them.

Note that for the 12 and 24V 'possibilities' the third diode would be the series diode with no voltage across with no load connected.
In case it's a 36V panel, all three diodes are bypass.

I'm curious what you'll come up with.

Best regards, Peter

FollowupID: 678734

Follow Up By: SmokeyD - Sunday, Mar 14, 2010 at 16:59

Sunday, Mar 14, 2010 at 16:59

Hi Peter,

Frustratingly, I am at work at the moment and can't count the cells on the panel. I know however that the panel size is (including frame) 122cm x80.5 cm. This equates to about 0.9 sq metres.
The panel was bought quite a long time ago (ebay job) by my son who probably didn't keep any info. He may have fiddled with things a bit I'm not sure. I will do some checking behind, (no chance of warranty anyway) to see what I can see. Bit unsure if I can upset the diodes by checking them though.

FollowupID: 678738

Follow Up By: SmokeyD - Monday, Mar 15, 2010 at 06:24

Monday, Mar 15, 2010 at 06:24

Hi Peter,

Got home last night and counted the cells - aaannd... there are 6 cells across the top and 9 down the side - I make that 54! They are however 5" by 5" and seem to be split in the middle - that would make it a count of 108. I didn't get a chance to measure the output (no sun), that would shed a bit more light I guess (pun intended).
More to come.

FollowupID: 678840

Follow Up By: Battery Value Pty Ltd - Monday, Mar 15, 2010 at 08:31

Monday, Mar 15, 2010 at 08:31

Allright SmokeyD, I can remember having seen square twin-cells before, so each 5"x5" segment actually consists of two 5"x2.5" cells right?
Then this would make it a 108 cell panel indeed.
Due to the fact that there are 3 diodes, I assume that this panel consists of 3 strings of 36 cells and that it can be configured into a 12V panel by paralleling the three strings.

I suggest to gain full access to all these wires and fuses and look out for 3 red wires and 3 black wires joined together on two terminals. Then the cathodes of all three diodes should be connected to the red wires, and the anode to the black wires.

If you find this, all is good and your 200W panel should be capable of giving its maximum at around 17.2V @ 11.6A in full sun.

If you find another wiring configuration, let us know and we'll figure it out.

Best regards, Peter

FollowupID: 678852

Follow Up By: SmokeyD - Monday, Mar 15, 2010 at 14:52

Monday, Mar 15, 2010 at 14:52

Peter,

Thanks for your efforts - truly without you guys here, I would have thrown the panel away by now and bought a new one. That's the only suggestion I have received from a number of solar shops. I will delve a little further tomorrow to see what I can see.

Just incedently, is this panel capable of supplying enough to run my 60w fridge and 3 LED lights through 2 x 75Ah batteries?

FollowupID: 678893

Follow Up By: Battery Value Pty Ltd - Monday, Mar 15, 2010 at 15:15

Monday, Mar 15, 2010 at 15:15

That's ok SmokeyD, glad to help.

Based on 4 PSH, your 200W panel is capable of producing 800Wh per day.
So you'd get a continuous power of 33.3 Watts out of it, if it's buffered by a battery.
Your batteries will see a drain of around 70Ah during the 16 hours of no or little sun, based on your fridge/LED load.

So if your fridge draws a constant 60W and you want some juice left for your LEDs, then you'd need to double up your installed solar wattage, i.e. 2x200W panels. But that's already border line.
Note that depending on your location, it might be necessary to install 3x200W to make up for the smaller amount of PSH and/or give you a little extra to play with.

Note the figures are average and there will be days when there just won't be enough sunlight in which case you'd have to find alternative charging sources because your batteries aren't big enough to sustain more than a day of no sun.

Best regards, Peter

FollowupID: 678898

Reply By: Member - John and Val - Sunday, Mar 14, 2010 at 16:44

Sunday, Mar 14, 2010 at 16:44

From the label, you have a 24V panel that has a peak power point of 36V and should deliver about 5 1/2 amps.

Your open circuit measurement of a bit over 20V though suggests it is a 12V panel, which would have a peak power point of about 18V.

Pity you've tampered with the potting on the terminals - either the label is wrong or it's not a 200W panel or only one half of the panel is working. Either way I'd be talking to the supplier.

Suggest measure short circuit current and open circuit voltage. If the panel is a 200W one, and is working properly, you should see either

1) the open circuit voltage about 40V and short circuit current about 5.5 A
or
2) open circuit voltage about 20V and short circuit current about 11A.

Case 1 suggests a 24V panel, case 2 suggests it is a 12V panel.

Either will probably have 36 cells, arranged as 2 strings of 18. For the 12V panel these are connected in parallel in the terminal block, for 24V they will be in series.

If you get about 20V (open circuit) with about 5.5A short circuit, then only one of the two halves is working properly. (or it's actually a 100W panel)

Something worth checking - What is the area of the panel? If its area is about 0.8 square metre, it is a 100W panel; it will need to be over 1.5 square metres to be a 200W unit.

Hope that's not too confusing to be helpful!

Cheers

John

J and V
"Not everything that can be counted counts, and not everything that counts can be counted."
- Albert Einstein

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AnswerID: 408786

Follow Up By: SmokeyD - Sunday, Mar 14, 2010 at 17:10

Sunday, Mar 14, 2010 at 17:10

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Follow Up By: SmokeyD - Sunday, Mar 14, 2010 at 17:11

Sunday, Mar 14, 2010 at 17:11

Sorry that should read J and V

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Follow Up By: Member - John and Val - Monday, Mar 15, 2010 at 08:19

Monday, Mar 15, 2010 at 08:19

The usual pattern is two (or more) strings of 18 cells in series. The strings (9 down and 9 back) produce the voltage required to charge a 12V battery. With 2 strings of 18 cells, the strings can be connected in parallel to produce twice the current, or in series to produce charging voltage for a 24V battery. In your case seems you have 3 of these strings (3x18=54 cells), and it's very unlikely that the panel is intended to charge a 36V battery, so we conclude that the 3 strings are wired in parallel to suit a 12V battery.

With an area of about 0.9 square metres it should deliver about 80 -100 watts at peak power point, about 20V open circuit and about 5.5A short circuit. To measure these you don't need to expose the diodes - don't connect the panel to anything - to measure volts, simply set the meter to measure volts and connect it to the two output wires. To measure current, switch to the 10A current range and connect the meter to the two output leads. The meter will act as a short circuit and give the current reading.

If you see about 20V and about 5A in strong sunlight you have a working panel of about 100W peak power suitable for 12V battery charging. If this appears ok, suggest re-cover the diodes etc with some epoxy - I use roof-and-gutter sealant for this sort of job (and many others too!) - it's waterproof and sticks to most things.

HTH

John

J and V
"Not everything that can be counted counts, and not everything that counts can be counted."
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Reply By: Member - Ed C (QLD) - Sunday, Mar 14, 2010 at 20:16

Sunday, Mar 14, 2010 at 20:16

Definitely something 'fishy' about that panel you have there......

A 200W, 24V panel will typically be around the 150 x 100 cm mark (1.5 sq.m)...

Are you able to find out from your son which ebay seller he purchased it from?

Wouldn't by any chance happen to be this mob , would it???

If so, that will explain why the panel is not what the label purports it to be :(

:)

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"He who lie underneath automobile with tool in hand,
....Not necessarily mechanic!!"

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AnswerID: 408827

Follow Up By: SmokeyD - Monday, Mar 15, 2010 at 06:58

Monday, Mar 15, 2010 at 06:58

Hi Ed C,

My son is not sure - but the brand on the back is Tong Lin. Not that that clears anything up. I did count the cells and found 6 x 9 which adds up to 54. They are 5" square but split in two, so that I guess adds up to 108 - which is odd. I will when I get a chance measure the output. That is where you measure across the diodes?

FollowupID: 678841

Reply By: _gmd_pps - Monday, Mar 15, 2010 at 12:14

Monday, Mar 15, 2010 at 12:14

Measure the outer size and get back with the measurements.
I have 2 200W panels. Each one has 54 Split cells (108).
One panel is roughly 150cm x 100cm and they deliver 53.7V in serial when connected to my MPPT controler. So each panel is around 27V when operating.
good luck
gmd

AnswerID: 408901

Follow Up By: SmokeyD - Monday, Mar 15, 2010 at 13:34

Monday, Mar 15, 2010 at 13:34

Outer measurements are 122cm x 80.5 cm

I have not hooked it up to a system yet as I want to ascertain what the dang thing is actually doing. I have yet to measure the current so that should make things a little clearer.

Cheers.

FollowupID: 678887

Follow Up By: _gmd_pps - Monday, Mar 15, 2010 at 13:49

Monday, Mar 15, 2010 at 13:49

I think this clears it up pretty nicely.
There is not enough difference in solar technology to produce a true 200W
panel in that size today. I think we are safe to assume that the specs are inflated
and that you actually have a 120W panel.
Your panel most likely works ok, just has inflated specs.
good luck
gmd

FollowupID: 678889