Normal power outout range for a solar panel throughout day/year

[Flyview]

Hi everyone,

I'm playing around testing my 100W 12V solar panel.

It's rated at:
Voc 20V
Isc 6.1A

I just tested it while pointed and tilted toward the sun around 10:50AM on Nov 25 in southern California.

I got 18.8V and a max of 3.65A.

Does this sound normal? Only 3.65A/6.1A = 60% of rated power output?


What's a normal range throughout the day and seasons?

[J.P.M.]

FWIW, At 1050 hrs, P.S.T. 11/25/2018 in zip 92026, the direct normal (beam) + diffuse irradiance was ~ 902 W/m^2 for a flat surface oriented normal to the sun.

If your device was pointed at the sun in So. CA at that time today, and the sun's irradiance was not attenuated/obscured by high cirrus as is prevalent around here today, that 902W/m^2 is ~ 0.902 of the likely STC of the device you're testing.

Today's clouds will change that 902 W/m^2 up/down from minute to minute, with that range ~ +/- 10 min. around 1050 hrs. from approx. 695 W/m^2 to about 933 W/m^2 as clouds come/go.

Today's somewhat unstable irradiance, at least as today is around my house, may not make for a good/reliable/SWAG testing environment. Days with no clouds, and I mean none, work best.

The question as you phrase it will not produce a meaningful answer.

[Flyview]

You're right, it was a bit hazy high in the sky around where the sun was. I tested close to noon and I got up to 4.2A / 6.1A (69%). So according to your numbers panels are measured at 1000W/m2 irradiance? In that case it should get the rated power as long as the sun's irradiance is at least that correct?

[SunEagle]

You're right, it was a bit hazy high in the sky around where the sun was. I tested close to noon and I got up to 4.2A / 6.1A (69%). So according to your numbers panels are measured at 1000W/m2 irradiance? In that case it should get the rated power as long as the sun's irradiance is at least that correct?

The Isc value is the short circuit amount of amps the panel can withstand. The best amp output that a solar panel can produce is the Imp value which is still hard to achieve outside lab conditions.

[Sunking]

Isc and Voc are for load calculations. Example 20 volts x 6.1 amps = 122 watts which ought to tell you something. The numbers you want to look at is is Imp and Vmp. So today 18.8 x 3.65 amps = 68 watts which is pretty good at 10:30 am. Peak will be thos very seconds at solar noon. So yes what you seen is normal.

[littleharbor]

Pull out the panel from a cool location. Connect your volt meter to it and place it in direct midday sun. As the panel heats up you can watch the voltage drop. Your panel, when cold should put out closer to listed Voc.

[Flyview]

Isc and Voc are for load calculations. Example 20 volts x 6.1 amps = 122 watts which ought to tell you something. The numbers you want to look at is is Imp and Vmp. So today 18.8 x 3.65 amps = 68 watts which is pretty good at 10:30 am. Peak will be thos very seconds at solar noon. So yes what you seen is normal.

Awesome ya you're right. I watched some YouTube videos to see what to measure. There's a lot of misinformation out there!

I forgot I can just calculate the output wattage from the measurements directly rather than get a percentage of a theoretical max and then apply it to the known 100W max!

Just for reference my Vmp is 18V and Imp is 5.5A.

[Sunking]

Awesome ya you're right. I watched some YouTube videos to see what to measure. There's a lot of misinformation out there!.

You Tube is the Idiots, err I mean Millineals Bible.

And 18 volts x 5.5 amps = 99 watts. You will never see that. At best you might see 85 watts for a few minutes around noon. FWIW Isc (short circuit) is at 0 Volts or 0 watts. Voc is open circuit which means no current and with no current is 0 watts.

Power (watts) = Voltage x Amps. 0 volts x 10000000000000000000000000000000000000000000000000 00 amps = 0 watts all day long.

[J.P.M.]

You're right, it was a bit hazy high in the sky around where the sun was. I tested close to noon and I got up to 4.2A / 6.1A (69%). So according to your numbers panels are measured at 1000W/m2 irradiance? In that case it should get the rated power as long as the sun's irradiance is at least that correct?

STC (Standard Test Conditions) irradiance is 1,000 W/m^2 normal to the device. STC panel temp. is 25 C.

You will probably not get the STC rating of 100 W from your device except under rare or few conditions. Some reasons:
1.) The normal (perpendicular to the solar device) irradiance components (direct and diffuse and reflected) will most likely never be => 1,000 W/m^2. Probably less most of the time. Today wasn't the best solar day, but it wasn't bad. Daylong output of my array was ~ 95% of a clear day's output. Long, boring story why.
2.) The operating temp. of your device will probably be > the STC rating temp. of 25 C. That higher cell temp. will lower the Vmp and power output more than it will raise the power output due to slightly higher Imp.
3.) The panel will probably be fouled (dirty) to some degree.

You're right, there is a lot of misinformation out there. A lot of it courtesy of the idiot's bible. Waste your time on that crap at your own risk.

[Paul Land]

Hi everyone,

I'm playing around testing my 100W 12V solar panel.

It's rated at:
Voc 20V
Isc 6.1A

I just tested it while pointed and tilted toward the sun around 10:50AM on Nov 25 in southern California.

I got 18.8V and a max of 3.65A.

Does this sound normal? Only 3.65A/6.1A = 60% of rated power output?


What's a normal range throughout the day and seasons?

All those ratings are under optimum lab test conditions even the panels listed watts ie:LG 300W are +- the listed rating. Cells are arranged on build table and like rubics cube the puzzle is set close to rated watts not exact.