how can you test your solar panel for wattage

[cdoug1946]

i have a used solar panel that was 80 watts. this year it seems to not work as well so i was told to test it with amp meter and it was around 18. then i was told to multiply it by 1.4 i think to get the wattage....does this make sense?

[Jason]

Hi and welcome!

Thanks for registering

Watts=Volts x Amps


also, i moved your thread to the "solar panel beginners" forum

[Mike90250]

i have a used solar panel that was 80 watts. this year it seems to not work as well so i was told to test it with amp meter and it was around 18. then i was told to multiply it by 1.4 i think to get the wattage....does this make sense?

Nope, bum info.

The calculation for wattage is volts X amps:

30v x 4a = 120w

Solar panels are a bit more tricky, since you are measuring short circuit amps.
Take the amps you measure, and multiply by the normal panel voltage (not the open circuit) Because the way PV panels work, you cannot measure exactly, but you can get pretty close - about 10% of actual.

[cdoug1946]

How can you test your solar panel for wattage

thanks for info. so first question.....i found the actual no....18.4 .....now first of all i am assuming that was amps (i had borrowed a tester from friend and i am assuming that no. is amps not volts?) and if so, now what do i do? find the voltage of the panel found somewhere? and then multiply by 18.4? thanks so much....i am surrounded by ignorance....thanks again.

[DeltaFox 25]

I was building a solar panel and with 36 cells ti will be around 20 volts and for each cell It is suppose to be 3.3 amps. Do you multiply this times 36.??? to get your wattage???.

[Mike90250]

A solar panel would, for example, be 17V and 3 amps. = 51W
17V @18A would 306w, which is highly unlikely.

Many panels have a sticker on the backside, with the factory specs. They list:
Open Ckt Volts
Short Ckt Amps
which are the two things you can check at home.

[DeltaFox 25]

Thank you. i just bought a clamp type meter to check amps but can not get it to work. Thank you.

[solardood]

Well the clamp meter is probably good for AC only. Just a guess, but on the back of the panel it should show the open circuit voltage, so take a reading in the bright sunlight and see what you get. Should be close to the spec. on the panel if it's relatively new.

[DeltaFox 25]

The panels I'm talking about are the one's I built. The meter is set up to read bouth ac & dc. Ouy sun here is not to good .This is the wrong part of the season. Like this morning I got 5 volts ont the meter because of the sun tilt. O'well I'll weight untill this spring I guess. I can hook up my new mppt 60 amp charge controler. and the rest of the wiring .

[Mike90250]

to test panels, you need bright, full sunlight. Measure open ckt volts, and short ckt amps, to the limit of your ampmeter

[DeltaFox 25]

I don't think we are suppose to get any good sun for awhile. I'll do that when It happens. Thank You Wayne

[cindynsg]

I used a hallogen lamp to test my cells and panels. Couldn't possibly be much brighter, but yikes it uses alot of juice, so be quick about it.

[Sunking]

For most consumers there is only two test you can perform.

Voc or voltage open circuit. You disconnect the panel and measure the voltage the panel generates with the panel facing directly inot the sun at noon, and then compare to the specs. The specs will list two voltages Vmp (voltage maximum power) and Voc. For a typical panel made for 12 volt battery systems Vmp will be around 22 volts and Voc around 17 to 18 volts.

The second test is Isc or current short circuit. This one is not quite so easy to measure, takes some knowledge, and a meter capable of measuring the amount of current the panel or system is capable of generating. Pros use a Clamp On type meter. With a Clamp-On meter you simply disconnect the panel and take the two wires coming from the panel and short them together, take a current reading with the Clamp-On meter with the panel facing directly into bright noon sun.

Some DMM's are capable of measuring current. However they are very limited as to how much current they can measure with 10 amps max on the higher end meters. I really do not suggest you try this unless you know exactly what you are doing and how to perform the measurement. So therefore I will not elaborate.

[john p]

Here is the most simple way to measure the output of a solar panel with only instrument needed is a cheap multimeter that is set on volts DC.. THIS METHOD CAN NOT EVER HARM THE METER THE PANEL OR ANYONE ELSE
First get from an electronics parts store 10 x5w 10 ohm resistors ,, Join all the resistors in parallel(lay them all together then twist all ends together so it now looks like just one fat resistor)
Connect each wire from the solar panel to one end of the resistor pack .
Place the solar panel out in the sun 2 times first about 9am then about 12 noon.
The reason for doing this is you now have a low light and full sunshine reading..Of course you need to do this on a bright sunny day.
Now set you multimeter to volts DC hold one probe from the multimeter to each end of the resistor pack take the reading.. Its totally safe
Now just multiply that reading by 14 and you will have a answer that is very close to the watts you are going to get from it when later connected to a solar charge controller and a battery,,

This is assuming the panel is designed for a 12v system if its for a 24v system then multiply by 28.
DO NOT leave the resistors connected very long to the panel while it is facing the sun . THEY WILL GET HOT.. BE CAREFUL WHEN YOU TOUCH THEM

[Mike90250]

...... THIS METHOD CAN NOT EVER HARM THE METER THE PANEL OR ANYONE ELSE ....DO NOT leave the resistors connected very long to the panel while it is facing the sun . THEY WILL GET HOT.. BE CAREFUL WHEN YOU TOUCH THEM

Ouch. a 200W panel will get those 50W worth of resistors pretty toasty.

I've never tried this method, always measured the open circuit voltage (it should match the sticker on the panel) and then measured the short circuit amps (it too, should match the sticker on the panel). Just need to know how to operate a meter, and most panels are under 10A, so that matches 95% of the meters with a 10A current measurement setting.

Mike