Solar Panel Output verse rating

[rom]

Originally Posted by sailorboy1

Still seeing 210-220W from my 290W panel under good conditions

May I suggest you ask around you how much the others get compared to their rating ? I would be interested in the result of such a poll.

[epiic]

Keep in mind that location is everything.

I make WAY more power here in Florida than I did in South Carolina.

[sailorboy1]

Originally Posted by rom

May I suggest you ask around you how much the others get compared to their rating ? I would be interested in the result of such a poll.

Well I thats what I asked in post 1. I never asked for anyone to "fix" my problem.

At the end of this first year of cruising I'll be deciding if it is worth it to add another panel. Right now it appears it is at least a 2 year pay back over running the generator.

[rom]

Originally Posted by sailorboy1

Well I thats what I asked in post 1. I never asked for anyone to "fix" my problem.

At the end of this first year of cruising I'll be deciding if it is worth it to add another panel. Right now it appears it is at least a 2 year pay back over running the generator.

Ask around you in palm beach not here on the forum There is no general agreement here, once again I think you should get close to 100% of STC rating.

[masonc]

Let's try to be clear about ratings. Your 100W panel is not rated at 100W. It is rated at 100W @ 25C. If you use a non-contact thermometer and measure the surface temperature of the panel, you will find it about 44C in the middle of the day, especially here in the tropics. With an inverse temperature coefficient of -0.5%, that means the rated output is 44-25 = 19*-0.5 = -9.5% = 95W

If you want to test your panbel's output, you need a test set like my Seaward Solar PV150. It has two units, one sits next to the panel and measures temperature and irradiance and transmits that data back to the test set. The test set measures voltage, current and insulation values. The complete data is recorded to a drive and can be used to calculate the real power of the panel.
PV Installation Testing White Paper | Seaward Solar
Yep, that's me doing panel testing.

[noelex 77]

Originally Posted by masonc

Let's try to be clear about ratings. Your 100W panel is not rated at 100W. It is rated at 100W @ 25C. If you use a non-contact thermometer and measure the surface temperature of the panel, you will find it about 44C in the middle of the day, especially here in the tropics. With an inverse temperature coefficient of -0.5%, that means the rated output is 44-25 = 19*-0.5 = -9.5% = 95W

Yes that is spot on. In an installed system there are also other losses.

The wire and any connections will have some voltage drop. The controllers voltage conversion is not 100% efficient and it will also have some self consumption.

However there are a couple of compensating factors. Illumination levels above the STC rating is possible. Also many good quality solar panels (on average) put out a little more power than their rating when new.

These factors mean recording the rated output, or even very slightly above this, is possible, but only under exceptional circumstances, and for brief periods of time.

Nevertheless, achieving the rated output, or close to it confirms the system is healthy

[rom]

Originally Posted by masonc

Let's try to be clear about ratings. Your 100W panel is not rated at 100W. It is rated at 100W @ 25C. If you use a non-contact thermometer and measure the surface temperature of the panel, you will find it about 44C in the middle of the day, especially here in the tropics. With an inverse temperature coefficient of -0.5%, that means the rated output is 44-25 = 19*-0.5 = -9.5% = 95W

If you want to test your panbel's output, you need a test set like my Seaward Solar PV150. It has two units, one sits next to the panel and measures temperature and irradiance and transmits that data back to the test set. The test set measures voltage, current and insulation values. The complete data is recorded to a drive and can be used to calculate the real power of the panel.
PV Installation Testing White Paper | Seaward Solar
Yep, that's me doing panel testing.

Right let's be clear about *STC* rating and allow me to correct you : 44-25 = 19*-0.5 = -9.5% makes 90.5W not 95W.
And let's also be clear that this is just an example ! Sunpower specs says 0.29% per °C, which in your example would make a 94.5W ouput.
And let's also be clear that STC also talks about brigthness and AM1.5, not only cell temp, and that AM1.5 especially can make a huge difference : please see post #72 by Barnakiel : http://www.all-science-fair-projects...91/0080-b3.jpg

Is that clear enough ? Is that useful for sailorboy1 ? I doubt it

[sailorboy1]

Originally Posted by rom

Right let's be clear about *STC* rating and allow me to correct you : 44-25 = 19*-0.5 = -9.5% makes 90.5W not 95W.
And let's also be clear that this is just an example ! Sunpower specs says 0.29% per °C, which in your example would make a 94.5W ouput.
And let's also be clear that STC also talks about brigthness and AM1.5, not only cell temp, and that AM1.5 especially can make a huge difference : please see post #72 by Barnakiel : http://www.all-science-fair-projects...91/0080-b3.jpg

Is that clear enough ? Is that useful for sailorboy1 ? I doubt it

I bet I know more than you even though you appear to be trying to be a forum expert. Wonder if that is clear enough for you, but I doubt it.

The thing with forums is people are looking to fix a problem so they can be experts even if they need to make up the problem to be fixed.

[rom]

Originally Posted by sailorboy1

I bet I know more than you even though you appear to be trying to be a forum expert. Wonder if that is clear enough for you, but I doubt it.

The thing with forums is people are looking to fix a problem so they can be experts even if they need to make up the problem to be fixed.

ouch that hurts ! Very sorry you take it that way as I was only trying to help you out and
trying as well to get better understanding of what to expect from my own panels.
Good luck with your system, cheers.

[masonc]

Originally Posted by rom

Right let's be clear about *STC* rating and allow me to correct you : 44-25 = 19*-0.5 = -9.5% makes 90.5W not 95W.
And let's also be clear that this is just an example ! Sunpower specs says 0.29% per °C, which in your example would make a 94.5W ouput.
And let's also be clear that STC also talks about brigthness and AM1.5, not only cell temp, and that AM1.5 especially can make a huge difference : please see post #72 by Barnakiel : http://www.all-science-fair-projects...91/0080-b3.jpg

Is that clear enough ? Is that useful for sailorboy1 ? I doubt it

Correct, 90.5%. Nearly ten percent less.
Why did I use 0.5%? That's the number we are taught to use in solar school, when there is no other data.
As to other losses, that's also correct, but you were discussing panel ratings, not system losses. I usually allow for 15% to 20% losses from STC to actual AC output. There's no point getting into very esoteric factors as people on the forum are trying to evaluate power output versus rated power without compensating for insolation, cell temperature, angle.
In my experience the ratings on panels are accurate, and the better panels have positive tolerance. However, for boat applications, the average user can't reliably tell any difference. Shading, wind, ambient temperature and reflection off the water will be bigger factors.

[noelex 77]

Originally Posted by masonc

As to other losses, that's also correct, but you were discussing panel ratings, not system losses. I usually allow for 15% to 20% losses from STC to actual AC output.

I think everyone is talking about system output rather than panel output.

The solar output on a boat can remain DC rather than always requiring conversion to AC like domestic systems.

[newhaul]

Don your output on the panels should be.close.to rated on 5 or 6 april at solar noon local.
That is if there is no cloud cover, no smog, and your panels are freshly cleaned. Other than that I suspect you are seeing what your panels are go ok ng to produce with the atmospheric and solar conditions you curently have at your location. Rob SV Meer Schaum.

[StuM]

Originally Posted by rom

I do not understand how Stu made the math in his post #12 and I actually tend to disagree with his conclusion.

In STC rating the angle of the sun to an horizontal panel is 48.2° (because of "AM 1.5", look at "air mass" on wikipedia) and solar radiation is 1000 W/m2

On the 4th of february you had an angle of 48° (!) and 970 W/m2 at the best moment of the day, that is around noon.

So, from my point of view you should have seen an output pretty close to 100% already taht day.

Please explain how 970W of radiation can project more that 721 W/m² at a 48° angle of incidence.

And note that that ignores "air mass" which you appear to misunderstand.

At 48° the suns rays have a lot more "air mass" to get through than when they are at 90° so the irradiance will be further attenuated.

[StuM]

Originally Posted by epiic

Keep in mind that location is everything.

I make WAY more power here in Florida than I did in South Carolina.

And time of year. In mid-to-high latitudes you will make WAY more power in summer than in winter in the same location.

[StuM]

Originally Posted by rom

Ask around you in palm beach not here on the forum There is no general agreement here, once again I think you should get close to 100% of STC rating.

Once again, that is physically impossible given his latitude and time of year.