Question re solar panels and regulators

silver-fox

silver-fox

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I currently have 2x 80 watt solar panels which generate a peak current of 9 amps and this is passed through a MPPT voltage regulator which is advertised as supporting a maximum current of 20 amps and a.notional maximum of 250 watts.

If I double the number of panels I expect to generate a maximum current of 18 amps but I will have increased the notional power of the panels to 320 watts, which is beyond the manufacturer's recommended notional limit of 250 Watts.

I simply don't understand the importance of "notional power" other than it is theoretical maximum in perfect conditions. Can anyone advise me if I am OK to proceed to 4 panels providing I don't exceed the maximum supported current of 20 amps?
 
Do you intend to connect the 4 panels in parallel and thereby generate 18A max at 20V-ish or will you use any in series and therefore keep the current down but increase the voltage, perhaps up to 40V-ish? What is the maximum voltage handing of the controller?

I would have thought that a controller that can handle 20A max would probably be competent to handle around 400W but perhaps yours has a lowish voltage rating.

Richard
 
Someone will be along soon who knows much more than me, however, my understanding is;
You cannot exceed the maximum voltage of the controller without causing damage to it. In respect of the PV wattage, I believe that if you use panels of a higher wattage than the controller is designed for it will simply “waste” the excess power and only deliver to its maximum value. However, controllers working a max for long periods will get warm.
 
silver-fox said:
I currently have 2x 80 watt solar panels which generate a peak current of 9 amps and this is passed through a MPPT voltage regulator which is advertised as supporting a maximum current of 20 amps and a.notional maximum of 250 watts.

If I double the number of panels I expect to generate a maximum current of 18 amps but I will have increased the notional power of the panels to 320 watts, which is beyond the manufacturer's recommended notional limit of 250 Watts.

I simply don't understand the importance of "notional power" other than it is theoretical maximum in perfect conditions. Can anyone advise me if I am OK to proceed to 4 panels providing I don't exceed the maximum supported current of 20 amps?
Click to expand...

What controller are we talking about ?
 
The panels are connected in parallel to a 12 v battery bank. Output at the panel is around 19v.
Current measured between voltage regulator and battery. The voltage regulator is made by Marlec for use with the Rutland 1200 and solar panels.
 
The MPPT controller will increase the current produced from the panels and under ideal conditions the output will be well above 9A from your existing 160w.

Your existing controller will handle 20A, which is more than enough for 160w, but not enough for 320w. Under ideal conditions the output from the controller would exceed 20A. However, the amount of power that is wasted will only be very small.


As the current will exceed the capabilities of the controller, it is important that the controller can limit the current to the 20A maximum. Nearly all controllers have this self protection mechanism built in, but you need to check your controller as this is not quite universal.

An alternative would be to keep your existing controller and use a second controller for the additional 160w of panels. Two controllers will produce a little more power, provide some redundancy and would be a little more reliable, as the controllers are not working close to their maximum capabilities or needing to engage their self protection mechanism.

An aditional controller such as the Victron 75/15 would be about £80.
 
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silver-fox said:
My two panels have never exceeded 10 amps, why should 4 panels exceed 20 amps? BTW, there is overcurrent protection, so can I suck it and see?
Click to expand...

If your current panels have not exceeded 10 amps as measured into the batteries it means the batteries have always been well charged and no/little load so do not take the current or you have not had sufficient sunlight at the right angle hitting the panels. Essentially 160w panel should give (max) 160 divided by 14 so 11.5 amps less the inefficiencies of the converter of about 5 to 10 %. Something like you get. For low batteries it would still be trying to deliver 14v (or more) to the batteries even when they are only at 12v so current remains the same.
So assuming the controller has an internal limit of 20 amps you should be OK. However I would be inclined to be doubtful of makers claim of 20 amps output capability (optimistic as with so many devices quoting max capability) I would go for less panels or 2 controllers. olewill
 
320w is capable of producing more than 20A output, but it will not happen often. Our previous yacht had 330w and peak outputs were around 25A. A 20A protection circuitry would have certainly been required to prevent damage, even scaling down to 320w.

It needs a good installation with low voltage drop in the wiring and a good controller capable of tracking the panels correctly. If your maximum recorded peak is under 10A from 160w it suggests there may be a minor problem with your system unless the panels are situated so that they cannot simultaneously receive direct sunlight.

silver-fox said:
BTW, there is overcurrent protection, so can I suck it and see?
Click to expand...
Looking at the manual for the regulator, it has some overcurrent protection, but unlike most regulators that reduce the current to stay within the limit, the Marlec regulator will shut down completely. It looks like it has to be manually reset, which will be annoying if the boat is left unattended and the current exceedes 20A.
 
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