How to test a solar output direct from panel?

[MattBW]

I have a new folding panel 160w compared with the older previous 50w one. Slimmer, better looking and far greater output.

However, there some marks on the front and a few imperfections which I wasn't pleased about and make me prone to send it back. However the vendor has offered a big discount if it's working fine. It will get marked in time anyway so I could be persuaded if the output is good. Of course he said plug it in see if its charging but that doesn't prove how much of its capacity its making nor that the PWM is efficient in any way.

I am dubious as to it's output which could be the rubbish PWM charge controller as at present the 50w panel puts more amps out but that could be difference in chargers.

How do I test the output in amps of the panel without a charge controller? I can see the voltage fine. If its ok I may just get a victron mppt to to go with it

 

[Andy]

I believe you need to put an amp meter inline on positive wire with panel wired up to a controller & battery.
If it produces volts near panel max in good sun lite I recon it should be OK.
How much is list on it ?
You need to use mppt controller to get best charge.

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[MattBW]

Thanks Andy. I got myself a Victron SmartSolar 75/15, I am going to try it with both panels and get an idea of the output from each. The app is rather good.

It was so overcast yesterday I couldnt get a thing out of the panel, it was barely making 16v.

 

[MattBW]

The Victron is indeed excellent and has given me a good insight into the panel.

160w in direct sunlight about 2pm UK yesterday the most I was getting was 3.2amps or 42-45w... Now I would never expect full capacity but this seems very low for 160w of panels to me but I could be wrong. My old 80w panel on my T25 would in summer put out close to 4amps The 50w suitcase put out 2.2amps on the same day same controller...

Does it sound like these panels are under-performing? They do have a few imperfections and a little crack in one cell which is why Ive raised a dispute with the seller.

I did put the battery under load to test.

 

[MattBW]

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[Skewif]

What sort of load did you use? The only time I see the maximum solar panel output is when either the batteries are well drained or I'm charging the bike battery which consumes more than the max the solar can produce.

 

[MattBW]

I may just be seeing a full battery in that case. I used all rear lights on (about 1.5a of load) and the webasto heater on startup.

As I have a separate NASA BM1 battery monitor I could see the battery was being drained by far more than the panel charger was putting back in.

I guess as the panel looks a bit ropey Im trying to decide whether to return or just accept a discount to keep it.

 

[Amarillo]

I did put the battery under load to test.

I have never seen more than ~6 Amps from my 200 Watt panels even when the battery is under load from our 12 Volt, 20 Amp kettle.



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[MattBW]

That is reassuring then, seems it's probably fine despite the damage..

 

[MattBW]

Does make me think my little 50w panel is actually pretty amazing for kicking out 2.2 amps then

 

[Amarillo]

Does make me think my little 50w panel is actually pretty amazing for kicking out 2.2 amps then

Maybe it's a quirk of the battery: it finds it easy to swallow 2.2 Amps from a 50 Watt panel, but much harder to swallow 8.8 Amps from 200 Watt panels.

I now wonder if the experience is different for Ocean owners with two leisure batteries.


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[Skewif]

Just saying but often see near and even over the rated 200W fitted. On a cloudless day can get a steady 12A+ when the sun is high, with roof down and enough load.

 

[MattBW]

Wow that's pretty interesting, I wonder if the number of leisure batteries makes a difference as Amarillo says.

 

[Amarillo]

Just saying but often see near and even over the rated 200W fitted. On a cloudless day can get a steady 12A+ when the sun is high, with roof down and enough load.

Next idle moment with a cloudless day I'll run another test. The charger is in the tailgate tool box and I have no other system to monitor solar output.


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[MattBW]

You've done mostly off grid though am I right, so even if you've never seen more than 6A you havent had any capacity issues?

I also need to work out what profile to use on the Victron for my 80ah lead acid.

I definitely think another leisure battery under the drivers seat is in order, if I can work it around the heater ducting.

 

[Skewif]

I also need to work out what profile to use on the Victron for my 80ah lead acid.

I'm just using the std profile, seems about right for an AGM from what I have read.

 

[MattBW]

I am using the same one too at the moment and seems close to the alternator levels of voltage but mine is lead acid not AGM hoping it wont cause any harm.

 

[Skewif]

I am using the same one too at the moment and seems close to the alternator levels of voltage but mine is lead acid not AGM hoping it wont cause any harm.

AGM is a type of lead acid battery. It's probably the type you have.

 

[briwy]

It makes a big difference where you are.
In the UK I think the maximum we ever got from our 100w panel was 81w. Regularly getting 90+ with 99 yesterday here in south of France. The angle of the sun makes the difference.

 

[Amarillo]

It makes a big difference where you are.
In the UK I think the maximum we ever got from our 100w panel was 81w. Regularly getting 90+ with 99 yesterday here in south of France. The angle of the sun makes the difference.

We were in the extreme north of Europe in the summer, and Southern Europe in the winter, so that makes sense.


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[Amarillo]

Overcast most of today. Cleared up a little at 3pm. 115 Watts in hazy sunlight, dirty panels with two roof topper bungees casting shadows.


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[Roger Donoghue]

Be interested to see a link to your 160W panel Matt - thee figures seem low.

For reference:

- A "framed" (regular bulky) 100w panel will kick out 6 amps max on a good sunny UK day with the panel angled facing the sun (i.e. at 90 degrees to the sun). This is with a PWM charger.
- Thin 100w panels kick out a little less as they can't dissipate the heat so well. Expect more like 5 to 5.5 amps.
- Solar regulators back off when the battery approaches full - expect to see the amps drop as it sails past 13 volts. The only way chargers (regulators) can judge how full a battery is is by looking at the voltage.
- If your battery is full, switching on a load will see the same amount of solar going back in. So turn on a fridge when the battery is full and expect (sun shine allowing!) the charge rate climb from 0.1 to 0.5 of an amp, to 4 amps (ish) depending on the fridge.
- to really test your solar setup you need to run your battery down to a point that it needs a full current bulk charge for long enough that you can watch it happening. Disconnect solar, run your fridge and other things for perhaps, the whole morning, then switch solar back on and watch the charge. Obviously choose a clear sunny day to get a valid result.
- If you ever see "float" charge on your Victron, do not expect to see big charging amps - this stage is supposed to be gentle.
- partial shading has a dramatic effect on current loss.

I'd expect a 160w panel, framed, to produce a peak of around 9 amps. Even with just one battery. The charging current is only limited by your panel, the charger, and how empty the battery is. Even a battery half the size would happily take 20 amps until it started filling up. The panel needs to be pointing at the sun, not layed flat.

 

[MattBW]

Hi Roger,

This is my panel, now seems to be on Amazon UK, although I have a Victron 75/15 with mine.

https://www.amazon.co.uk/dp/B07DW8PBNM/?tag=eliteelect-21.

You will see my 3 star review on Dokio on there

It was flat on the ground but I did test it at high sun.

 

[Roger Donoghue]

Hmm - surface area stacks up with 160w. Ratings (11 amps) a touch optomistic. Should produce around 9 amps by my reckoning. Might just be the battery voltage was high enough to slow it down.

Flat on the floor would cost you around 20% or more.

 

[MattBW]

Hmm - surface area stacks up with 160w. Ratings (11 amps) a touch optomistic. Should produce around 9 amps by my reckoning. Might just be the battery voltage was high enough to slow it down.

Flat on the floor would cost you around 20% or more.

Best I've seen is 3.5amps under load, even in this sun but the battery was about 70% I believe.

I need to run it down a bit and try again.