More Solar for "Us"
Ok, I went off.the deep end? Bought 3 used 37watt uni-solar panels and a blue sky 2000e controller for the hefty price of $400, They were being listed as 75w panels, they are not The tested open...
Forum Discussion
There still seems to be some confusion in how to calculate the amps to the battery for MPPT and PWM comparisons.
For MPPT with its buck converter it is all about watts, where with PWM, watts don't matter.( Also with PWM there is no "working voltage"--just battery voltage)
EG, using 260w of panels in each case ( a 260 for the MPPT and a 160 and 100 in parallel for the PWM) Full high sun for each case at 25C ambient, 50C panel temp (the usual situation for panel heating then--as I have measured it too in the summer as reported in the past)
A. MPPT 260w. Heat loss =10% power at 50C so 260-26= 234w. Line loss panel to controller 2% (1-3 is decent) 234 x2/100 = 4.7 so 234-4.7 = 229.3w controller input. Controller efficiency 97% so controller output is 222.4w
Assuming no line loss controller to battery--Amps to battery is output watts /battery voltage. Using 13.5v = 16.48 amps
B. PWM 260w. You get Isc amps to about 13.5v (see IV curves)
Isc 100w panel = 6.2a and 160w = 10.1 so total Isc = 16.3 amps
So they are nearly equal.
You can get better results for MPPT with a lower battery voltage and less panel temperature, but as you all know, battery voltage in the morning with solar on, is over 13v on the way to 14.x, so picking a battery voltage in the 12s is just for "spin" as used by MPPT controller salesmen.
Their other spin fav is to claim that PWM fails to use all the panel power, while MPPT does, so PWM "wastes" all that power. Note the actual power from the MPPT in the above.(222 out of 260) Neither MPPT nor PWM gets all the power to the battery. But who cares? It is amps that charge the battery, not power.
For MPPT with its buck converter it is all about watts, where with PWM, watts don't matter.( Also with PWM there is no "working voltage"--just battery voltage)
EG, using 260w of panels in each case ( a 260 for the MPPT and a 160 and 100 in parallel for the PWM) Full high sun for each case at 25C ambient, 50C panel temp (the usual situation for panel heating then--as I have measured it too in the summer as reported in the past)
A. MPPT 260w. Heat loss =10% power at 50C so 260-26= 234w. Line loss panel to controller 2% (1-3 is decent) 234 x2/100 = 4.7 so 234-4.7 = 229.3w controller input. Controller efficiency 97% so controller output is 222.4w
Assuming no line loss controller to battery--Amps to battery is output watts /battery voltage. Using 13.5v = 16.48 amps
B. PWM 260w. You get Isc amps to about 13.5v (see IV curves)
Isc 100w panel = 6.2a and 160w = 10.1 so total Isc = 16.3 amps
So they are nearly equal.
You can get better results for MPPT with a lower battery voltage and less panel temperature, but as you all know, battery voltage in the morning with solar on, is over 13v on the way to 14.x, so picking a battery voltage in the 12s is just for "spin" as used by MPPT controller salesmen.
Their other spin fav is to claim that PWM fails to use all the panel power, while MPPT does, so PWM "wastes" all that power. Note the actual power from the MPPT in the above.(222 out of 260) Neither MPPT nor PWM gets all the power to the battery. But who cares? It is amps that charge the battery, not power.
