How do you know what is a good solar panel.

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24th July 2021, 06:05 PM
DiscoDB

….and add a PWM solar controller and that’s another 20-40% loss in efficiency.
24th July 2021, 07:40 PM
drivesafe

Quote:

Originally Posted by Ferret

The other thing which must be remembered when interpreting claimed power figures for portable panels is the standard ratings on which the claims are made are, I think, quoted at constant temperature. 25C I think.

The only time a panel in the real world will be near a constant 25C is when it is in the shade. Put it in the sun and it will heat up and de-rate.

I love demonstrating this by allowing a panel to sit in the sun for a few hours, measure the wattage and then pour water over the panel and watch the wattage rapidly clime as the panel surface cools.

I've been working with solar panels for well over 30 years and while I have leant some very useful info in this thread but the one thing that is probably the hardest to determine is, how long will a specific brand of solar panel actually be useful for.

My two oldest panels, one about 30 years old ( 150ma ) and the other ( 90w ) would be close to 20 years, and both these panels have stickers on the back of them, listing there specs and stating they are "Products of Australia"

Not something you see on too many panels today.

Over the last 20 years I have bought quite a few different sized panels, for the jobs they were required for, all were small, ranging from 2w up to 20w and many of the older ones have little chance of producing their marked wattage.

Does anyone have any way of determining true quality of solar panels?
24th July 2021, 08:12 PM
johnp38

Quote:

Originally Posted by drivesafe

I love demonstrating this by allowing a panel to sit in the sun for a few hours, measure the wattage and then pour water over the panel and watch the wattage rapidly clime as the panel surface cools.

I've been working with solar panels for well over 30 years and while I have leant some very useful info in this thread but the one thing that is probably the hardest to determine is, how long will a specific brand of solar panel actually be useful for.

My two oldest panels, one about 30 years old ( 150ma ) and the other ( 90w ) would be close to 20 years, and both these panels have stickers on the back of them, listing there specs and stating they are "Products of Australia"

Not something you see on too many panels today.

Over the last 20 years I have bought quite a few different sized panels, for the jobs they were required for, all were small, ranging from 2w up to 20w and many of the older ones have little chance of producing their marked wattage.

Does anyone have any way of determining true quality of solar panels?

you short the leads thru an ammeter and measure the current while also using a light meter to measure the watts per square metre and calculate against the stc

So if the panel is stickered at 8 amps (short circuit current) at stc (1000 W square metre @ 25 degrees C) and your light meter is saying 500 watts per square metre and the ammeter is measuring 4 amps then the panel is ok.

To get really fussy you would get the temperature coefficient of the panel from manufacturer specs and also allow for the percentage reduction (if hotter than STC) in output based on the ambient temperature of your testing environment.

The correlation of short cct current to solar intensity is linear.
24th July 2021, 08:38 PM
drivesafe

Thanks John, what I am after is a means of testing a panel, if such a test exists, to determine if the panel is good for a couple of decades of use, or if it is likely to give up the ghost a few years after buying it.

As I posted above, my older panels are fine, but the newer ones are no longer supplying their naked wattage.

I test everything I buy, including solar panels and while many are fine when first purchased, most just do not last that long.

The smaller panels are cheapies and I guess I get what I pay for, but if I were in the market for large panels, I would like to be able to carry out some form of test to see whether they are likely to be a good long term investment.
24th July 2021, 09:03 PM
johnp38

Quote:

Originally Posted by drivesafe

Thanks John, what I am after is a means of testing a panel, if such a test exists, to determine if the panel is good for a couple of decades of use, or if it is likely to give up the ghost a few years after buying it.

As I posted above, my older panels are fine, but the newer ones are no longer supplying their naked wattage.

I test everything I buy, including solar panels and while many are fine when first purchased, most just do not last that long.

The smaller panels are cheapies and I guess I get what I pay for, but if I were in the market for large panels, I would like to be able to carry out some form of test to see whether they are likely to be a good long term investment.

I think we all want that up front test !!

The only test for longevity is the in service test of time. No crystal ball tests that I currently know of.

As panels are current limiting maybe a couple months in the sun with the connectors short cct then check short cct output as per my previous post, if it has degraded under load in that short time trash it or at least use but don't buy any more.

Unfortunately if the panel you test is the manufactures single '1 out of every 10000' dud you get the wrong impression !

The best close to new output panels I ever came across were well over 20 yr old BP branded panels (who knew an oil company was into solar back then) and that was about 2012 I think , still in service with a lead acid storage bank.

Sticking to CEC accredited panels is not foolproof but a good start.
25th July 2021, 02:08 AM
drivesafe

Thanks again John and my two oldest panels are BP Solar and the oldest one was acquired from their factory/assembly plant in Sydney, around 30 years ago.
25th July 2021, 06:21 AM
windsock

Quote:

Originally Posted by drivesafe

Does anyone have any way of determining true quality of solar panels?

Best I can do is refer you to an independent test lab website where the test reports are freely available on registration. I think there are still test reports dating back to around 2014 or so. Just need to register and download. Not only is the PV cells tested but also the Bill of Materials that comprise the rest of the module.

PVEL | Bankability Testing for the Solar Industry
25th July 2021, 06:51 AM
Vern

Quote:

Originally Posted by drivesafe

these panels have stickers on the back of them, listing there specs and stating they are "Products of Australia"

Not something you see on too many panels today.

Does anyone have any way of determining true quality of solar panels?

That because no panels are made in Australia anymore.

Yes pretty sure we can test panels with our irradiance testers and other gizmos, thats more for our engineers than myself.
Quite offen i have tested panels onsite and they performed higher than their specs say.
25th July 2021, 09:50 AM
windsock

1 Attachment(s)

Quote:

Originally Posted by johnp38

The best close to new output panels I ever came across were well over 20 yr old BP branded panels (who knew an oil company was into solar back then) and that was about 2012 I think , still in service with a lead acid storage bank.

Quote:

Originally Posted by drivesafe

...my two oldest panels are BP Solar and the oldest one was acquired from their factory/assembly plant in Sydney, around 30 years ago.

I am about to redeploy a 20 year old BP275 (75W) panel soon to charge a 12V battery that will power an electric fence energiser and to provide some very occasional makita battery powertool recharging capacity. The panel still ticks over so will be interesting to see what the output is after 20 years. Been in storage the last few years so i hope it still works now it is just out of it's power warranty period... [biggrin]

Attachment 172465
25th July 2021, 11:32 AM
350RRC

Quote:

Originally Posted by windsock

I am about to redeploy a 20 year old BP275 (75W) panel soon to charge a 12V battery that will power an electric fence energiser and to provide some very occasional makita battery powertool recharging capacity. The panel still ticks over so will be interesting to see what the output is after 20 years. Been in storage the last few years so i hope it still works now it is just out of it's power warranty period... [biggrin]

Attachment 172465

I was offered any number of BP batteries by a third party about 10 years ago, a long time after BP got out of solar.

$100 each, had never been filled with acid, i.e. never used. Dunno if they're still around.

DL

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