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Open Roads Forum  >  Tech Issues

 > Determining Wattage of Solar Panels?

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Woodtroll

Appalachian Mtns, SW Virginia

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Posted: 08/14/12 07:09pm Link  |  Print  |  Notify Moderator

Hello, folks,

Years ago, I bought two used PhotoComm, Inc. MSVX-24 solar panels. That's pretty much all the information that is on the tag, and attempts to search these panels' specs out have been fruitless. I know how to test for voltage and short-circuit amperage, but based on these readings how do I figure out what these panels will actually return to my batteries through my Morningstar Sunsaver 6 charge controller?

Thanks,
Regan


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harold1946

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Posted: 08/14/12 07:27pm Link  |  Print  |  Notify Moderator

www.ampstowatts.com
If the amp output is not listed,put the panel in full sun, read the amps and then do the conversion.


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Woodtroll

Appalachian Mtns, SW Virginia

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Posted: 08/14/12 07:49pm Link  |  Print  |  Notify Moderator

Thanks, folks. I just wasn't sure what voltage to multiply the amps by- 12, 14 out of the charger, 17 out of the panel, etc.? From what BFL13 says, it looks like I'm complicating it too much! I'll test the panels the next sunny day we get when I am home at noon, and post the numbers.

I appreciate your help! Take care,
Regan

MrWizard

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Posted: 08/14/12 07:31pm Link  |  Print  |  Notify Moderator

you have the numbers
just compare them to the values for available panels

or post the numbers here and we will give you are best guess

since these are most likley 12v system 24rated watts
being used on a 6 amp controller

if i put an amp meter on the circuit , it will likely show just over 3 amps charging


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BFL13

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Posted: 08/14/12 07:30pm Link  |  Print  |  Notify Moderator

Based on my limited experience, the Isc you take at high noon is pretty close to what the panel will do for amps into the battery at high noon. Ignore Voc, it is just goofy--use the Isc which works ok.)

Two panels will do twice that. You need a way to get your full daily AH haul, depending on the 'bell curve' you get for amps all day depending on your location and time of year. A Trimetric is good for that job)

Your actual panel wattage does not matter very much in real life. The way they work is that the max power (panel rating in watts) occurs with fewer amps than Isc (called Imp at Vmp) --it's all BS. Ignore it. Just get your max amps at high noon on a sunny day with the panel oriented properly (South tilted up for your Latitude and time of year) and work with that.

Here are the amps I got various ways, so you can take your noon amps and plot your own bell curve in proportion.

http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/26065604.cfm


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BFL13

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Posted: 08/14/12 08:29pm Link  |  Print  |  Notify Moderator

Sorry, I was ASSuming the Voc would be around 20 so it is a 12v system at 17ish volts Vmp.

You can have 24v system with Isc in the 8a range. So my post above would not apply if it is a 24v system.

* This post was edited 08/14/12 08:37pm by BFL13 *

Woodtroll

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Posted: 08/15/12 04:44am Link  |  Print  |  Notify Moderator

No need to apologize- your assumption is right! It is a 12-volt (nominal) system. Your post is very helpful. I'll put the numbers up (probably tomorrow before I have a chance to get the readings) and let y'all see what you think.

Thanks again!

Woodtroll

Appalachian Mtns, SW Virginia

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Posted: 08/16/12 05:11pm Link  |  Print  |  Notify Moderator

Hello, folks,

I managed to test these panels today in somewhat less than full sun (about 3:00 in the afternoon). I got readings on both of 20.9-21.0 volts open circuit and 1.29-1.30 amps short circuit, depending on how I juggled the panels, meter, connections, etc. with only two hands! It looks like these are at least 24-watt panels, I think (?).

Thanks very much for your help! Safe travels,
Regan

Woodtroll

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Posted: 08/16/12 05:43pm Link  |  Print  |  Notify Moderator

mexbungalows wrote:

Are those panels with cells on a white background that may be yellowing in places?


They do have a white background, but no yellowing that I can see. The white shows through only as very fine margins- almost all the panel is covered by the cells.

MEXICOWANDERER

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Posted: 08/16/12 05:32pm Link  |  Print  |  Notify Moderator

Are those panels with cells on a white background that may be yellowing in places?

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