Solar Panel Output verse rating

[sailorboy1]

I'm been watching my solar panel output the last few days. I'm currently in Palm Beach getting lots of sun. But in the middle of the day with my 5 year old 290W panel with a MPPT controller in full sun is only putting out 170-180W and I know the batteries aren't limiting it to that amount.

What are others experience in real output verse rating?

[catsketcher]

I love having 400 watts of panels (2 x 200w). I have never seen 36 amps but once I think I got close to 28 or 30. The breadmaker was on and sun was overhead.

I can rotate my panels to be better orientated to the sunlight, that gets some more juice in. Also you can swish them with water to cool them down - they don't work as well when they are hot. Apart from that the long 6 metre run of cable at 12 volts wouldn't help with up to 30A running through it - lots of heat loss.

I don't know how they test panels but maybe the light at Palm Beach is not as strong as somewhere else - or in the test lab.

cheers

Phil

[dlymn]

My guess that panel rating is done by getting one solar cell, placing it in a place that has the highest solar radiation in the world, moving it so that the cell is at perfect right angles to the sun measuring when the the sky is clear and the sun is overhead, recording that measurement and the calling that rating as the rating for every cell in every panel produced. In other words, the rating is a measure of output in optimal conditions and has a loose connection with reality.( a bit like car fuel consumption numbers).

Our 6kw home system has never hit 6kw. Dirt over cells, sun angle, boat movement, shading by sails,wires and poles, dirty connections, long leads inefficiency of electronic components in the charge line and possibly more factors all work to reduce actual output.

[Empty Pockets]

And what are you still doing in Palm Beach?

[Stumble]

Originally Posted by dlymn

My guess that panel rating is done by getting one solar cell, placing it in a place that has the highest solar radiation in the world, moving it so that the cell is at perfect right angles to the sun measuring when the the sky is clear and the sun is overhead, recording that measurement and the calling that rating as the rating for every cell in every panel produced. In other words, the rating is a measure of output in optimal conditions and has a loose connection with reality.( a bit like car fuel consumption numbers).

Our 6kw home system has never hit 6kw. Dirt over cells, sun angle, boat movement, shading by sails,wires and poles, dirty connections, long leads inefficiency of electronic components in the charge line and possibly more factors all work to reduce actual output.

They are actually tested in a lab with a strobe light (no time to heat up the panels) putting out 1050w/m^2, placed directly over the cell at a temp of 72f (I think). It's a pretty idealized rating, but so long as they are all tested the same way the practical effects should scale.

[Paul L]

Panels are rated in a standard temp and radiation situation. Getting 75% of rating while mounted on a boat in good sun is pretty typical.

[john61ct]

Why not serial more rather than parallel them all, wouldn't you be better off using higher voltage like 80-90v over long runs?

[sailorboy1]

Originally Posted by john61ct

Why not serial more rather than parallel them all, wouldn't you be better off using higher voltage like 80-90v over long runs?

Heck I'm pushing 6 amps through a 8 gage wire. I'm not concerned about voltage drop

[tkeithlu]

And you're of the "don't blow smoke up my rear" persuasion? You think solar panel sales departments rate them at a average orientation average day dawn to dusk output as far north as Palm Beach?

[PaulinOz]

6 x 327watt Sun Power Panels best output ever 131 amps, theoretical max aprox 160 amps.

[donradcliffe]

I'd start to suspect the MPPT controller. What is the voltage on the panel side, and is it anywhere near the MPP??

[StuM]

Originally Posted by sailorboy1

I'm been watching my solar panel output the last few days. I'm currently in Palm Beach getting lots of sun. But in the middle of the day with my 5 year old 290W panel with a MPPT controller in full sun is only putting out 170-180W and I know the batteries aren't limiting it to that amount.

What are others experience in real output verse rating?

Palm Beach is 26°N
Sun is currently 16°S. so the maximum angle of incidence on horizontal panels is only 48%.

So about 60% of rated output is as good as you will get.
175 is about 60% of 290. So it looks as though your panels are performing exactly as expected.

Edit: That's about the same as you'd get at 10:15 and 16:30 in the same location in mid June. You'll get a lot more between those two times, peaking at almost rated output at 13:20.

Added: Your current daily output will be about the same as you would get in the same location in mid June if you switched your solar off between 10:15 and 16:30

One last addition:
http://www.pveducation.org/pvcdrom/c...lar-insolation
If you play around with the sliders on the second graph, you will see that at 27°N, you are currently at a daily total of 4.6kWh/m² with horizontal panels, compare to a mid Jun total of around 11kWh/m²
(or IOW, your panels are only giving you about 40% of the daily Watt hours that you will get there in mid summer)

[barnakiel]

Testing single panels without a controller I always get to within 95% of the rated output.

The main limiters: the batteries (if not discharged), the controller (if too primitive or faulty), the wires (if too small or corroded), the panels (if faulty, non-angled, shaded or otherwise compromised), the Sun (if overcast, low or otherwise compromised).

Cheers,
b.

[sailorboy1]

Originally Posted by donradcliffe

I'd start to suspect the MPPT controller. What is the voltage on the panel side, and is it anywhere near the MPP??

the input voltage is 32-33V and is the MPP for the panel

[noelex 77]

Originally Posted by sailorboy1

I'm been watching my solar panel output the last few days. I'm currently in Palm Beach getting lots of sun. But in the middle of the day with my 5 year old 290W panel with a MPPT controller in full sun is only putting out 170-180W and I know the batteries aren't limiting it to that amount.

What are others experience in real output verse rating?

This output is a little low.

I think one useful data point is the absolute maximium you have recorded from the panels. The higest output is likely to be obtained only briefly, but it does say something about the health of your sytem (voltage drop etc).

You should record resonably close to the rated output in ideal solar conditions especially if you angle the panels to the perfect orientation. Even a little over the rated output is possible.

What is the best you have seen?