Solar panel current variation ?

[Jake Royd]

Reasearching solar panels at present.
Looking at max current I note that an expensive one (Photonic universe) lists max current at 9.9A for a 200w panel.
Lots of Ebay cheapies list it as around 5-6A for the same wattage.

Is this true?
Why is it?
I accept it may just be that the cheaper ones are just crap panels ?

I was comparing monocrystallines.

TIA

 

[tonyidle]

It depends on how it's measured and on panel voltage. Normally quoted as short-circuit current making voltage irrelevant.

 

[Misterg]

Is this true?
Why is it?

Can be...

The 5 to 6 amp panels are likely ~40V nominal voltage, whereas the ~10 amp ones are likely ~20V nominal voltage - its just that the cells are wired up in a different combination of series/parallel within the panel.

For a PWM controller (charging 12V) the lower voltage would be (much!) better, but it doesn't make much difference for MPPT controllers, provided they can take the higher voltage.

You may find that the lower quality panels have higher s/c current and higher o/c voltage for the same output power as better panels. This is because the losses within the lower quality cells are greater when actually generating power.

 

[SomeoneElse]

Reasearching solar panels at present.
Looking at max current I note that an expensive one (Photonic universe) lists max current at 9.9A for a 200w panel.
Lots of Ebay cheapies list it as around 5-6A for the same wattage.

Is this true?
Why is it?
I accept it may just be that the cheaper ones are just crap panels ?

I was comparing monocrystallines.

TIA

Yes the current can vary on a 2 to 1 basis as some panels are designed for 12V and some for 24V systems. Remember power is volts times current. So doubling the voltage needs only half the cuurent for the same wattage. Some controllers can use a 24V panel to charge a 12V battery, some can't.
Make sure all your components (battery, controller and panel) are compatible.
Also don't confuse short circuit current with max-power current.

 

[Off da Grid]

A solar panel can give more than the rated volts and amps given the right conditions
They are actually more efficient when cold, it is possible to get more power on a frosty clear sunny day if the panel is angled correctly than in the height of summer when it’s very hot.
So your controller needs to have a safety margins of 10% above your panel size.

A pwm controller will waste the extra power of a large solar panel ( mine around 255watt 8.3 Amp 30.5 volts open circuit from memory) or cluster as the panels would be pulled down to the voltage of the battery 12.8v nominal.
An mppt controller depending on conditions takes the extra volts around18 of them and convert that to amps maybe even close to double the amps if your battery is fairly discharged therefore charging your batteries quicker.
It’s the amps you want.
When you drop the volts you up the amps the power in watts stay the same.
Best case senario not accounting for loses in the system.
255w / 30.5v = 8.36A
255 / 12.8 = 19.8A
They are also better in low light and cloudy days, but a decent one like Votronic aren’t cheap.
Also the higher the volts from the panel the less voltage drop you get over the length of your cables.

See the altE store channel on YouTube Amy does some brilliant videos on all the different types of controllers and solar setups to get the best out of your system.

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[Jake Royd]

Interesting isn't it. Using W/IxV then a 200w panel at say 20v no load voltage should produce about 10A.
But of course the voltage is pulled down to may be 14v by charging and by the regulator.
This

 

[Jake Royd]

Sorry about the above post. I’d started to ramble on and hadn’t noticed I’d pressed the post key.
Yes, the voltage of the whole system at the battery end is pulled down to the battery charging voltage probably about 13v

 

[DBK]

Sorry about the above post. I’d started to ramble on and hadn’t noticed I’d pressed the post key.
Yes, the voltage of the whole system at the battery end is pulled down to the battery charging voltage probably about 13v

The voltage is only "pulled down" by some of the cheap controllers. An MPPT type controller converts the higher voltage of the panel to the optimum charging voltage and increases the amps in the process. So you might have 5 amps coming from the panel but 8 going in to the batteries.

Panel voltage is dependent on the number of cells on the panel. I wouldn't get too hung up about this, it is the panel wattage which is important.