Usefulness Of MPPT Technology
This isn't a trick question. I wish to take a "Short Course" in the reality versus hype of MPPT control... Users who have MPPT and can report real-life experience... Let's say I get a pair of panel...
Forum Discussion
My proven method for calculating "expected amps" when pointed at a high sun, blue sky, with PWM is:
panel watts/130 x 8.2 = A
It has worked out right in real life using several different amounts, so it is fairly accurate, based on panels having an Isc proportional to a 130w with 8.2 Isc
So 360w should get you 360/130 x 8.2 = 23 amps. (note some mono panels have lower Isc per watt so they come out less, but most poly seems to be in the ball park)
Now what happens with MPPT? Most reports are that you get the same or a bit more, maybe 10% more tops. So your expected max amps with MPPT on 360w would be say 26 amps instead of 23.
Note there are some claims that the MPPT does better in the shoulder hours so you get extra AH per day than just comparing the expected max amps. No figures on that if true even. Say you get 15% more daily haul but just the 10% more max amps? No idea.
Note your controller whether MPPT or PWM should have an amps size 20% more than your expected max amps because there are times the solar does more amps than rated (edge of cloud effect is one) so for 26 amps expected, you should have a 30a controller. Some MPPT controllers clip the amps above their rating, so with them you can go to max, no 20% margin needed (eg Morningstar 15L ) With some PWMs they will let the amps through, but get too hot running above rated amps.
The other thing with controllers is their rated max voltage intake--total Voc of panels. One more volt than that for one second and you fry your controller! Yipes! So you need to figure the total Voc of your array when it is as cold out (when Voc is highest--not the rated Voc at 25C) as you will ever be camping and then allow some more margin besides to be safe.
In juggling panels and controller options you can have more than one controller, say if two smaller ones are cheaper than one big one. Same total amps on the battery.
panel watts/130 x 8.2 = A
It has worked out right in real life using several different amounts, so it is fairly accurate, based on panels having an Isc proportional to a 130w with 8.2 Isc
So 360w should get you 360/130 x 8.2 = 23 amps. (note some mono panels have lower Isc per watt so they come out less, but most poly seems to be in the ball park)
Now what happens with MPPT? Most reports are that you get the same or a bit more, maybe 10% more tops. So your expected max amps with MPPT on 360w would be say 26 amps instead of 23.
Note there are some claims that the MPPT does better in the shoulder hours so you get extra AH per day than just comparing the expected max amps. No figures on that if true even. Say you get 15% more daily haul but just the 10% more max amps? No idea.
Note your controller whether MPPT or PWM should have an amps size 20% more than your expected max amps because there are times the solar does more amps than rated (edge of cloud effect is one) so for 26 amps expected, you should have a 30a controller. Some MPPT controllers clip the amps above their rating, so with them you can go to max, no 20% margin needed (eg Morningstar 15L ) With some PWMs they will let the amps through, but get too hot running above rated amps.
The other thing with controllers is their rated max voltage intake--total Voc of panels. One more volt than that for one second and you fry your controller! Yipes! So you need to figure the total Voc of your array when it is as cold out (when Voc is highest--not the rated Voc at 25C) as you will ever be camping and then allow some more margin besides to be safe.
In juggling panels and controller options you can have more than one controller, say if two smaller ones are cheaper than one big one. Same total amps on the battery.
