Understanding Panel Ratings

[EssexBoy]

Hi All

I've been looking on ebay at the large wattage solar panel, but have been confused by the ratings I've been reading, such as this one:

The panel is a 250W one, so my maths says 250W/12V = 20.83A, but the label says max current = 8.41A
Now, I think this is because my MPPT controller does the clever bit & turns the max voltage stated as 30.33 into 12V & provides the 12.42A I think I'm missing? this means that I can almost ignore Max Volts and Amps ratings and concentrate on it being true 250W?
Could one of our more cleverer patrons put me straight please?
Thank you
Steve

 

[DBK]

The figures on the panel are correct. For max power the panel needs to be at 33.33 volts when it will be pushing out 8.41A. Multiply those together and you get 255W.

A good MPPT controller (I recommend Victron but might be biased ) will sort the input side out and do the charging stuff automatically.

 

[EssexBoy]

I have one of the MPPT controllers recommended by Andy Techno...

So, I think I'm right in saying then that this panel may be inputting 8.41A at 30.33V at the controller but all I really need to worry about is that it will be 12 to 14.4V (for battery charging purposes) and about 20A on the output of the controller?

In short, the config of the 250W input to the controller isn't important, as long as its in the range of the controller.

 

[DBK]

I have one of the MPPT controllers recommended by Andy Techno...

So, I think I'm right in saying then that this panel may be inputting 8.41A at 30.33V at the controller but all I really need to worry about is that it will be 12 to 14.4V (for battery charging purposes) and about 20A on the output of the controller?

In short, the config of the 250W input to the controller isn't important, as long as its in the range of the controller.

Yes, the controller can cope with a range of input voltages but will bring them down to the correct level for charging. Mine copes with two panels in series producing up to around 40 volts. The voltage is reduced by the controller but the current is increased so give or take the odd percentage for losses you get all the power going into your batteries the panel can produce.

Volts(in) * Amps(in) = Volts(out) * Amps(out) (ignoring losses )