Is this solar panel wired correctly?

**Sunking** · 12-01-2011, 11:24 PM

OK first you have two wrong assumptions. You cannot take Voc x Isc to determine the wattage of the panel. When a solar panel operates at Voc current = 0. When operating a panel at Isc voltage = 0. 0 * X = 0 everytime. What you are missing is a solar panel is a current source, not a voltage source.

Next current out of a solar panel is proportional to the amount of sunlight striking the surface, assuming it is operating into a low impedance. I assume you are in the UK correct? You are never going to see full output in the UK, especially in these winter months, so 6 amps does not sound that far off to me.

**rossco** · 12-01-2011, 11:38 PM

Hi Sunking,

Thanks for the quick reply.

I stay in South Australia so the sunlight is pretty good here compared to the UK!

Looking at similar solar panels, they all have Open Circuit voltage and Short Circuit current figures included.
This is what I have been comparing my figures to.

Should the Voc and Isc not be the maximum possible as they are not under load?

On googling 'how to test a solar panel' I got the following information:
"To test a used solar panel, set your voltmeter to DC volts, and measure across the + and - terminals of the panel. This is called the "open-circuit voltage." A 12 volt panel should show about 21 volts in full sun. Panels designed to be connected in sets of 4 (4 panels in series) will show 4 to 5 volts. If your meter can measure DC amperes, set it for this (on a high enough range so your meter won't go up in smoke) and connect it between the + and - terminals in full sun. This measurement is called the short circuit current, and is how much current you can expect from the panels. For a 12 volt panel, multiply your current by 17 volts to get watts. (17 volts is the rated voltage of most 12 volt panels.) "

If I take my short circuit current (6a) and x by the 17V= 102W. I know this is rough but it seems if the panel is not outputting anywhere near the amps for 200W/12V.

I am now sketching the layout of the cells on the panel. It may not be accurate as I am not disassembling the panel. Purely using a bright spotlight to follow the interconnects/traces.

Cheers.

**rossco** · 12-02-2011, 12:08 AM

As promised, here is quick sketch of what I can identify from the panel wiring.

200W Solar Panel.jpg

I assume the 4 wires at the top connect to the junction box but don't take my word for it!

The 2 lower red wires at top of panel are hidden behind the cells but I have sketched where the seem to go to.

Hope this helps someone. Any advice is appreciated!

**Sunking** · 12-02-2011, 12:10 AM

Voc = voltage open circuit. In any open circuit no current can flow.
Isc = current short circuit. There is no voltage in a short circuit because there is no resistance to develop a voltage... So it makes no difference if you measure Voc or Isc the power always = 0 because 0 times any number equals 0

All panels have four basic specs with respect to voltage and current. Two of them you know of Voc and Isc. The other two are:

Vmp = voltage at maximum power point
Imp = Current at maximum power point

You cannot measure Vmp or Imp. You can only measure Voc accurately and ISC you can only get a crude measurement because you have no idea what the light level is. I can tell you that you will never see a panel develop full Isc spec.

Now let's go back to the four specifications. Here are the specs of an actual 135 watt solar panel made for 12 volt battery systems.

Voc = 22.1
Vmp = 17.7
Isc = 8.37
Imp = 7.63

Now you tell me what the power is using Vmp x Imp, and then for Voc x Isc and see what you think. So if you assume Voc and Isc are operating conditions you get 185 watts which is dead wrong, the right answer is you get 0 watts.

As to your panel wiring problem, leave all four wire open. Measure DC voltage between each of them in sun light. Identify each of the 2 series of cells. You should measure about 22 to 24 volts between each pair of wires and note the polarity. Once you have the two positive leads and the two negative leads identified; Connect the two positive leads together, and the two negative leads together...

Then retest Isc and Voc. Assuming you have noon bright sun you should see about 22 to 24 Voc, and 10 amps or more Isc.

**rossco** · 12-02-2011, 12:31 AM

I appreciate the stated Panel Watts is based upon the Vmp x Imp.

The label on the back of the panel states VMP 18.0V and Current is 11.2A (L).
Not sure what the (L) stands for.

I would assume that the Isc will also be higher than the Imp?

If that is the case, my panel is only providing Isc of 6a. Even if the Imp somehow managed to match that:

Vmp= 18
Estimated Imp= 6
Watts= 108

Would this be fair?

What I am trying to work out is if the panel is cabled wrongly.

When is was originally delivered, I measured Voc of 35,7v and Isc of 7.0A. Again, these figures are expected to be higher than the Vmp and Isc figures. But Watts would equal 35.7x7= ~250W

In comparing to a 200W 24V solar panel description:
"
Max Power: 200W
Max Power Voltage: 36.5V
Max Power Current: 5.19A
Open-Circuit Voltage: 46.2V
Short-Circuit Current: 5.61A
"

Comparing my Vsc and Isc figures to above (46.2x5.61= 259W)

Would it be fair to say that my panel seems to be capable of performing to the 200W stated, it justs need to be cabled correctly to reduce the voltage (parallel connection instead of series?) and increase the amps?

Thanks for all your help! I appreciate that my figures aren't Vmp or Imp, but it's the only figures I can go with at the moment.

Cheers.

**Sunking** · 12-02-2011, 12:44 AM

Based on what you have said, you had to of wired it incorrectly. Read my last post, last paragraph for resolution.

**rossco** · 12-02-2011, 01:19 AM

Ok, sort I had it fixed following your instruction but still not working.

Here are results of Voltmeter across junction box with nothing else (wires/diodes) connected.

Junction Box has 4 connections. Number following for results
1 2 3 4

Negative always on left number.
1-2= 11.1v
1-3= 22.2v
1-4= 33.2v

2-3= 11.1v
2-4= 22.2v

3-4= 11.1v

I then assumed that junction point 1&2 were negative and 3&4 were postive.

Connected 1&2 with wire, same with 3&4.
Measured voltage and got 11.4.

Have I missed something or is the panel really wired wrong?

**Wy_White_Wolf** · 12-02-2011, 10:17 AM

Originally posted by rossco

As promised, here is quick sketch of what I can identify from the panel wiring.

[ATTACH=CONFIG]1516[/ATTACH]

I assume the 4 wires at the top connect to the junction box but don't take my word for it!

The 2 lower red wires at top of panel are hidden behind the cells but I have sketched where the seem to go to.

Hope this helps someone. Any advice is appreciated!

That diagram shows the panel having 60 cells. I don't see how this could be used as on 12V or 24V system. 12V panels usually have 36 cells and 24V would have 72 cells. One could use it on a 12V with a MPPT controller. For 24V you would have to wire at least 2 on them in series with an MPPT controller.

I'd say this panel was designed for high voltage grid systems and not for use on battery systems without MPPT controller. I say the seller is not being honest as to what he sold you.

WWW

**Wy_White_Wolf** · 12-02-2011, 10:21 AM

Make and Model Number of Panel

I don't see where you ever stated what the make and model number of the panel is. It should have a spec label on it somewhere.

WWW

**rossco** · 12-02-2011, 08:03 PM

Here is picture of the label.

IMG_0514.JPG

Yes, I agree that is seems to be few cells short of a expected panel size!

So here is the current situation.
Purchased panel for $400.
Found faulty and tried all of the above with the supplier.
Best I could get was 22v and 6a at .
Supplier offered to refund the money completely and collect panel OR I could keep the panel for $150.
I've decided to keep the panel for $150 and try and identify where the fault is and hopefully get the best possible out of it.

What would be my next step?

Following the suppliers instruction to connect cable between point 3&4 in junction box, I get 23v and 6a (Voc & Isc).

Worst case scenario, I case I should hope I get 5a at 18v when connected via regulator. ($150 for 100W panel)

Is there anything else I can try or attempt to reconfigure the wiring? The connections/voltages don't make sense to me. I would have expected 2 x 30cells joined in parallel.

All help is greatly appreciated!

**Wy_White_Wolf** · 12-02-2011, 09:56 PM

Sounds like the seller is pulling one over on you. Take a look at what I found on Ebay

Pardon our interruption...

http://www.ebay.com.au/itm/24V-190W-Solar-Panel-/230666122742

The Panel is rated at 190 watts, 36.0 VWP, and 5.56 amps

Here's another reference to the Panel

solar panel mystery

http://www.exploroz.com/Forum/Topic/76847/solar_panel_mystery.aspx

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....

**rossco** · 12-02-2011, 10:52 PM

Pictures of actual panel

Here are couple pictures.
This one shows the size of the cells.
IMG_0516.JPG

And here is picture of the 6x10 cell layout.
IMG_0515.JPG

My panel seems the same as the link you provided. Only difference is my label says 18v, 11.1A.

Would an MPPT controller provide more than the ISC of 6A I get when join terminals 3&4 in junction box?

I have ordered a Juta 30Amp Intelligent controller.

Do the voltages I get across the 4 terminals make sense as to how the cells have been connected? I would expect the voltages in pairs with no common connection.

Looks like I may have to purchase another panel as leave for camping in 2 weeks time.

**rossco** · 12-03-2011, 01:27 AM

Will this MPPT Regualtor resolve my problems? (Solar problems that is!)

To all the gurus.

We have worked out I have been sold a 24v 200w solar panel even though specs on website were:

Max Power:
200W
Open Circuit Voltage:
21V
Max Power Current:
11.11A
Max System Voltage:
1000V

So after finally getting an acceptable refund from the supplier, I have ended up with the panel for $150.

If I now purchase an MPPT regulator, will this be suitable for charging my 12v battery?

Here is the regulator I am looking at:

http://www.gsl.com.au/products/solar_regulators.html#product1

Model: MPPT12-1

Capable of 12A and my Isc of 7A, I believe it should be suitable?

Any input, as always, would be greatly appreciated!

**Sunking** · 12-03-2011, 10:46 AM

Originally posted by rossco

If I now purchase an MPPT regulator, will this be suitable for charging my 12v battery?

Here is the regulator I am looking at:

http://www.gsl.com.au/products/solar_regulators.html#product1

Model: MPPT12-1

Capable of 12A and my Isc of 7A, I believe it should be suitable?

Yeah it should work

Is this solar panel wired correctly?

Is this solar panel wired correctly?

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