Solar strategy in the east
I'm from Illinois. Camping out in the AZ desert at the moment, I can see that solar is easy out here. Do the math, install it right, and you are golden. Camping in the eastern 2/3rds of the US, i...
Forum Discussion
CA Traveler wrote:BFL13 wrote:
Nerd here. When a PWM 12v loses voltage from 21 volts (12v panel) it still has plenty to be over 13v so amps don't suffer. MPPT (37v "24v" panel) makes its amps from voltage so it does suffer if voltage goes down.
Wow - lets look at reality using your example. The 12V panel loses 7V or 7/21 of its power. So a 100W panel can only deliver 67% of its power with a PWM controller. The same panel with a good MPPT controller would lose only about 8% of its power.....
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The 100w panel cranks out 6.4 amps until battery voltage reaches about 13.5 then amps drop slightly till battery voltage reaches 15v and then amps crash (IV curve)
So at full amps at say battery 13v, watts is 6.4 x 13 = 83.2w So who cares if the panel is not producing all of its 100w, it is still cranking out full amps. (it's amps you want into the battery)
That is why PWM can "afford" to lose some voltage; you still get the amps. MPPT can't afford that. Look what happens to amps with MPPT when the panel loses voltage in the heat of the mid-day sun. Ouch! Meanwhile Isc (which PWM uses for amps) goes up in the heat. :)
