Solar Panel "Question"

[ova50]

Is there a way to check what wattage a solar panel is.
Our van has two panels on the roof, one is definately a 200watt panel, but the other has no sticker or info attached.
It is smaller in size than the 200watt Panel.
:cheers:

[Cuppa]

Measurement of the panel’s surface area & then comparing to others for sale would give you a reasonable indication & is probably the easiest method.

Alternatively a DC capable clamp meter around one of the two cables coming from the panel in full sun will tell you how many amps it’s putting out. Combined with a measurement of panel voltage it should give an indication of panel size. Watts = Volts x amps. (However because of various factors panels will generally supply less than their rated output). Eg. in a nominal 12v system if a panel were putting out 6.6 amps in full sun into a discharged battery it would be reasonable to assume it was a 120w panel 17v x 6.6amps = 112.2 amps.

[BillsGU]

Measurement of the panel’s surface area & then comparing to others for sale would give you a reasonable indication & is probably the easiest method.

Alternatively a DC capable clamp meter around one of the two cables coming from the panel in full sun will tell you how many amps it’s putting out. Combined with a measurement of panel voltage it should give an indication of panel size. Watts = Volts x amps. (However because of various factors panels will generally supply less than their rated output). Eg. in a nominal 12v system if a panel were putting out 6.6 amps in full sun into a discharged battery it would be reasonable to assume it was a 120w panel 17v x 6.6amps = 112.2 amps.

This would only work if your battery was very low in charge and therefore has a very low (and known) resistance. The current a panel supplies is dependant on the load resistance therefore to check it accurately you would have to disconnect the solar panel from the regulator and put a high wattage low value resistor across the panel output terminals.

Then you could use the formula Power = Current squared X Resistance, and by using your clamp meter measure the current, square the result and multiply this by the resistance value.

Sounds complicated - but its not really.

[Cuppa]

This would only work if your battery was very low in charge and therefore has a very low (and known) resistance. The current a panel supplies is dependant on the load resistance therefore to check it accurately you would have to disconnect the solar panel from the regulator and put a high wattage low value resistor across the panel output terminals.

Then you could use the formula Power = Current squared X Resistance, and by using your clamp meter measure the current, square the result and multiply this by the resistance value.

Sounds complicated - but its not really.

I agree, which is why I made reference to a discharged battery, & suggested that measuring the panel’s surface area was probably the easier method.I expect that what you suggest would be more accurate, but I think my suggestion would be good enough to determine panel wattage.

[threedogs]

bummer you lost the sticker lol
But I would measure it against a known brand and size

[ova50]

bummer you lost the sticker lol
But I would measure it against a known brand and size

TD, have measured it but nothing I have compared is of the same size.
It may be a BP panel as some paper work I have seems to suggest a BP panel.
I did phone them but little info was given.
:cheers:





Measurement of the panel’s surface area & then comparing to others for sale would give you a reasonable indication & is probably the easiest method.
Alternatively a DC capable clamp meter around one of the two cables coming from the panel in full sun will tell you how many amps it’s putting out. Combined with a measurement of panel voltage it should give an indication of panel size. Watts = Volts x amps. (However because of various factors panels will generally supply less than their rated output). Eg. in a nominal 12v system if a panel were putting out 6.6 amps in full sun into a discharged battery it would be reasonable to assume it was a 120w panel 17v x 6.6amps = 112.2 amps.

Thanks Cuppa,
I thought I may have been able to count the cells and that may have given me an idea.
Do you think this meter would show the watts if it was wired between the panel and the regulator?
http://www.ebay.com.au/itm/LCD-Voltage-Power-Analyzer-Watt-Meter-Ammeter-Battery-Balance-Amp-RC-Charger-AU-/271290101743?hash=item3f2a266fef#ht_4485wt_1001
:cheers:

[Cuppa]

Yes I think it would, with the proviso made by BillsGU.
If it were me I’d still just measure the surface area. Eg. If it was approx 75% of your 200w panel it would be reasonable to assume it was approx 150w give or take a watt or two.

[ova50]

Yes I think it would, with the proviso made by BillsGU.
If it were me I’d still just measure the surface area. Eg. If it was approx 75% of your 200w panel it would be reasonable to assume it was approx 150w give or take a watt or two.

Thanks Cuppa, will measure them both, and see what I come up with., when it stops rainning.
Should mention I somehow double posted, and deleted it:)

[threedogs]

what size is the panel Ova ??

[ova50]

After measuring I think it is most likely a 120watt panel.
Have also ordered the watt meter and will hook that up to see if it will show the watts etc.
Thanks Guys