Solar panel

[capsco]

I have just purchased a 24v 100amp panel, the spec gives 29.2 open circuit voltage, does this mean that measured direct at the panel with no other connections I should see this voltage? the sun is shining at the moment.

 

[greenalien]

That's correct. However, there's probably a blocking diode in one of the output wires, to prevent the battery discharging back through the panel when it's dark, and there will be a voltage drop across this, probably half a volt or so.

 

[capsco]

Thanks that is what I feared, I did see 25.8 briefly when I first connected, now I have 24.4, any ideas?

 

[elton]

I have just purchased a 24v 100amp panel, the spec gives 29.2 open circuit voltage, does this mean that measured direct at the panel with no other connections I should see this voltage? the sun is shining at the moment.

100 Amp? 2.4 Kw?

 

[capsco]

100 Amp? 2.4 Kw?

You spotted the deliberate mistake.

 

[greenalien]

The quoted voltage is probably the maximum obtainable in bright (mid-day, mid-summer) sunshine with the panel pointed straight at the sun, with no shadows across it and no dirt or other contamination on the panel.

 

[capsco]

Those conditions have all been met apart from, we are 2 hours away from mid-day.

 

[VicS]

the spec gives 29.2 open circuit voltage

You sure that's right? For a 24 volt panel i'd expect a good bit more than that.

Open circuit volts for my 12v panel according to the spec is 19.6 volts so would expect double that for 24 volts.

You will need about 28 volts under load to effectively charge a 24 volt battery

 

[capsco]

Sorry Vic don't know how to post a link but E Bay item no 220834895932

 

[VicS]

Perhaps its a mistake and it should read 39.2 open circuit volts. ... thats double my 19.6 for a 12 volt panel.
Maybe the volts at maximum power, but still a bit low for that even.


Easiest way to post a link is to simply copy and paste the URL. Usually works just occasionally the forum software doesn't like it.

http://www.ebay.co.uk/itm/220834895...e-All-Categories&_fvi=1&_rdc=1#ht_3601wt_1139.

Proper way is to use the "Insert link" icon,

Then then immediately type in what you want to appear in the post while the blue high lighted bit is still blue:

eBAY SOLAR PANEL

 

[nigelmercier]

Thanks that is what I feared, I did see 25.8 briefly when I first connected, now I have 24.4, any ideas?

You don't have it connected to the battery by any chance?

 

[capsco]

No Nigel, that is no connection at the batteries

 

[ccscott49]

Thanks that is what I feared, I did see 25.8 briefly when I first connected, now I have 24.4, any ideas?

That sounds like a 12volt panel.

 

[VicS]

That sounds like a 12volt panel.

I dont think you would see voltages that high on a 12 volt panel.

If you can find a spec for a 12 volt panel with OC voltages that high then fair enough but I don't think I have seen any.

 

[capsco]

It looks like I may be better off with 2 x 80w 12v panels from the same company, wired in series, would this seem so to you techs?

 

[ccscott49]

It looks like I may be better off with 2 x 80w 12v panels from the same company, wired in series, would this seem so to you techs?

Thats what I use, only I have four, two wired in series then paralleled.
I show 38v open circuit on mine.

 

[pappaecho]

The suppliers clearly quotes an open circuit voltage of 29.2 volts, which does seem low. My 12 volt panel is about 19 volts. open circuit In bright sunlight at 3.30 pm today my solar panels has the batteries at 14.2 volts. At lunchtime ( pouring rain) they were 13.2

 

[VicS]

It looks like I may be better off with 2 x 80w 12v panels from the same company, wired in series, would this seem so to you techs?

Technically there is no benefit in using two 12 volt panels in series. It may make them easier to fit.

I think there is a misprint in the ebay description, but you have to be careful with ebay suppliers.

 

[capsco]

Which panel do you think the misprint applies to?

 

[pappaecho]

Having read up on the PV forum, it turns out that there are apples and pears.
"Older type" solar panels were produced for 12v and 24 volt operation, which was essentially connection to lead acid batteries, 12 24 or 48 volt configurations.
To do this, 36 wafers were connected in series as the optimum, and then banks of 36 connected in parallel to give the optimum charge range in diffent solar conditions.

With the onset of grid tie inverters, which did not have strict 12, 24 or 48 volt levels, it was found to be more appropriate to change the wafter configuration to give 18 volts nominal, as the inverters will work on 90 to 12 volts dc. Obviously there are no normal 18 volt battery banks.

The spec of your panel suggests to me that it is an "18 volt" PV panel for connection to the grid tie inverter system ,

Normal true 24 volt panels have a VOC of 42-44 volts, and a VPM of 28-29 volts.
As you are getting a VOC in bright sunlight of 29 that should give a VPM of about 22-23 which suggests an 18 volt nominal panel.

I suggest that you access a PV solar forum, as it looks like you have been sold the wrong panel, possibly in error. They can direct you through a series of tests to confirm its true voltage/amperage outputs