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simple question about solar panels  RSS feed

 
M Foti
Posts: 171
Location: western n.c.
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I just hit the motherload and got a bunch of free panels yay, I love when good things happen! anyhow, I'm trying to figure things out here in regards to solar pv panels... This whole efficiency thing has me confused.

Here is my question, and please, lets try to stay on topic (haha, I'm the worst for thread derailment)... a panels RATED output, meaning the sticker on the back of the panel, will that panel EVER produce that much amperage and if not, what is "normal" percentage wise of that RATED output? I understand there are variables, so please lets not get too involved in all that mess, just tell me what YOUR panels do on a typical sunny day, do they produce what your sticker says, or not? If not, what is a number to be expected? 50%? 75%? 100% I'm looking for round-a-bout ballpark numbers here, no need to get too technical.

thanks a bunch
 
M Foti
Posts: 171
Location: western n.c.
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So, I guess I answered my own question. Maybe this will help someone else in the future who is looking for answers... I have a stack of 25 solar panels with shattered glass, they came from a commercial solar farm near a golf course, you can do the math. Bummer that the yuppies would destroy something like that, but worked out good for me haha... anyhow, ONE of them was in perfect condition, it just had a chip on the aluminium frame. These were all between 235 and 220 watt panels from Canadian Solar.

anyhow, the ONE good one, on a sunny winter day was producing 60% of rated capacity, so just north of 5 amps. Almost all of them were producing in the high 3's and a few were right at 5amps with the good one. so, looks like they have slightly diminished productivity, but not a ton... Should make quite a nice little solar setup. Too bad the TVA (tennessee valley authority) will not allow one more watt of solar to backfeed into their grid... so, I can't do a grid tied system that should be illegal, maybe it'll be fixed soon enough.
 
Terry Brown
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the panels will very very rarely get near their design limit - mine havnt yet... its only april...

the local authority wont allow you to connect to the grid?? - ahh you mean they wont pay you for generating.... more like.

not to worry tho - if you have your own at least they can power summink.

the ones to the grid cant be separated from it [well mine cant] would be nice to have the option to flip the charging from grid to house at will.. come the apocalypse I will have power.. lol
 
Chris Olson
Posts: 84
Location: Northern Wisconsin
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M Foti wrote:If not, what is a number to be expected? 50%? 75%? 100% I'm looking for round-a-bout ballpark numbers here, no need to get too technical.


With MPPT your solar panels will produce nameplate power at STC (Standard Test Conditions, which is cell temp of 25C and 1,000 watts/m^2 irradiance. If the cell temp is hotter than 25C there is a de-rate factor. If it is colder the panels will produce more power. We have several arrays with 1.5 kW in each one and I have seen the individual 1.5 kW arrays producing ~1,750 watts in 20 below weather in bright sunshine many times.

Direct hooked to a battery without MPPT, or using a PWM controller, you will rarely if ever get more than 78% nameplate capacity in perfect conditions. 60% is more the normal with solar panels direct hooked to a battery.
 
Markus Loeffler
Posts: 30
Location: Altadena, CA, USA
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M Foti wrote: the ONE good one, on a sunny winter day was producing 60% of rated capacity, so just north of 5 amps.


60% seems low, what value from the back of the panel where you using as the 100% value?
Also what type of charge controller where you using?

Markus
 
Topher Belknap
Posts: 205
Location: Midcoast Maine (zone 5b)
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M Foti wrote:...a panels RATED output, meaning the sticker on the back of the panel, will that panel EVER produce that much amperage and if not, what is "normal" percentage wise of that RATED output?


Evaluating solar panels is best done by measuring the energy output. That means finding a good load, and measuring kWh (kiloWatt-hours) with an appropriate meter.

I recall a huge news hype about a kid finding a better way to arrange solar panels, sadly he was measuring voltage...

That said, a panel perpendicular to the sun's rays on a clear day should produce pretty near the panels rated wattage.
 
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