Newbie Qn from Madagascar re 200 watt PV panel with 39v Voc and 24v charge controller

Radcol · September 2015

Greetings from Madagascar!

I am a newbie to your forum trying to make sense of a system I have bought for a project in rural Madagascar. We bought two 200w PV panels with the following listed specifications:

Max Power: 200w
Open circuit voltage 21.6v
Operating voltage: 18v
Short circuit current: 9.17A
Operating current: 8.33A
Max system voltage: 1000v
Power tolerance: 3%

The seller also sold us a 12/24v 20A charge controller to go with this system.

We also bought two 150Ah 12v batteries.

Now that we are installing the system on the school, I checked the PV panel (Open circuit) voltage and get a reading of 39 volts on each panel. This is considerably higher than the 21.6v listed on the specs plate on the back of each panel, and although they told me at the time the panels were made in Germany, I suspect they were made in China and I am not sure I can trust what it says on the back.

So, my question is this: If the actual (meter tested) Voc is 39 volts, before making any connections to any other components, can I assume that the 24v charge controller will handle this as an initial input voltage, or will this "correct itself" once the components are connected, or should I be looking for a 36v charge controller instead? I don't want to burn out any components right from the beginning and would rather be safe than sorry. Thanks in advance for any suggestions or recommendations you can give.

Colin.

vtmaps · September 2015

Welcome to the forum.

Some panels are configurable. That means there is a junction box on the panel that allows the panel to be wired as a (nominal) 12 volt or as a 24 volt panel. Perhaps that's what you have... otherwise, I can't think of a reason why you would measure 39 volts open circuit.

Whether your controller can handle it that voltage (and handle it efficiently), what make and model controller do you have?

--vtMaps

Radcol · September 2015

Hi vtMaps!

Thanks for your response! The Charge controller is marked as "Jarrett" brand, but has no model numbers or other specs listed on it (and no manual/instruction booklet either! It only has a sticker on the back that says 12/24 volts, 20A. Like many things electronic sold in this country, it is often made in China, no matter what the label says, and is often imported only because it is cheaper. However, as I was not expecting anything much to go wrong with a PV panel, I was surprised to find such a large disparity between the stated Voc and the actual voltage when measured via a meter. That's why I'm asking here on this forum before trying to connect anything up for the first time.

Thanks in advance for any further advice.

Colin.

BB. · September 2015

Double check you volt meter--Take a voltage reading on one of the batteries and see if it is close to what you expect.

Also, make sure you keep the batteries properly charged--Batteries that sit around unused (and uncharged) and they can go bad if they they are uncharged for much more than 1 month.

-Bill

Radcol · September 2015

Hi Bill!

The voltmeter is working fine and indicates a battery charge of 13.8 volts, so no problems there. I remember from installing a hybrid system in another project a few years back that they advised the three wires from the wind turbine should be short-circuited before connecting to the charge controller, however, I don't think that advice would apply to a PV panel. I should add that the 39 volts was measured on the open circuit when the panels were in mid-morning full-sunlight, however, I would think that a measured actual Voc should be at least within the same ballpark figure as the open-circuit voltage reported on their specs label (21.6v +/- 0.5 v).

Any other ideas/suggestions?

TIA,

Colin.

BB. · September 2015

39 volts Voc sounds just about like two "12 volt panels" (Voc~21 volts) in series.

It is not very common these days, but there were panels that you could rewire for 12 or 24 volt operation (as vtMaps said).

And in one case, there were some panels that were simply miss-marked. They were much higher voltage than listed on the label.

If you have a 10 amp full scale amp meter--Try measuring the short circuit current of one of your panels in full noon-time sun (pointed directly at sun).

If the sky is clear, you should read sort of close to Isc. If you measure less than 1/2--Then I would suspect that the panel is miss-marked.

There is another "standard" of Vmp~30 volts -- And that is very common for ~200 watt panels. How many cells does the panel have, and what is their setup (rows x columns).

A Vmp~30 volt panel should have 60 cells. A Vmp~36 volt panel would have 72 cells (and a Vmp~17 volt panel would have either ~36 cells, or 72 cells if they are in series/parallel).

-Bill

Radcol · October 2015

Thanks Bill!

That's exactly the type of info and advice I need for checking this out further. I will get back to you as the panels are already mounted out at the project site (a few hours out in the countryside) but not yet connected. I will check ASAP. Thanks again. Colin.

Photowhit · October 2015

While you are there, you might take a picture of the junction box, if it has a removable cover pull it off and take a picture inside.

zoneblue · October 2015

Its pretty unusally to get 18v Voc panels in 200W configurations. Most 200W+ panels are 30-45 Voc.
As others said measure the voc, count the number of cells. If theres 60 cells and the Voc is 30ish, then the panels are simply mislabelled, being a normal grid tie panel. If theres 72 cells, then the dual configuration panel the others mention is a possibility. A standard 72 cell panel is normally only found in 300W+ panels. Thats because the std cell size is now 150mmx 150mm.

Radcol · November 2015

Hi guys! Sorry it has taken so long to get back to you. I finally have word back from out at the rural school site and they have confirmed that the panels have 72 cells (each 15.5cm x 10.5cm) for each panel. They also measured a short circuit current of 2.14 amps on a cloudy day and 7 amps on a clear sunny day. So, in light of this, do you think I am likely to run into problems with the 12/24v 20A charge controller they sold us? What do you recommend?

Again, many thanks in advance for taking the time to advise from half-way around the other side of the world!

Photowhit · November 2015

My guess is that the panels are hooked up in series, and that is why you are measuring 39 volts. In direct sun light (+ or - 2 hours from solar noon) and angles toward the sun, I would expect more current (amperage) than is being measured.

Was the panel lay out/connections checked (as Bill suggested earlier)?

Is this set up as a 12 or 24 volt system?

Newbie Qn from Madagascar re 200 watt PV panel with 39v Voc and 24v charge controller

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