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
IMO
the real gain of MPPT is with higher voltage panels, 20v's or more at the controller
example the 2000e can accept 30v input, batteries are charged at less than 1/2 , batteries are charged at 13.6 to 14.2v
30v panels would create 14v output "earlier in the day OR with bad weather" before my 17v panels do, so they would start charging sooner ( just a few amps into the controller ) before mine even start to have any usable output, then as the sun climbs and the voltage goes up the MPPT controller converts the excess higher voltage into amps
some controllers can take 70v input
any way a 100w panel at 17.2 volt produces 5.8amps max at 100 watts and 17.2v
a 100w panel at 30v would produce 3.333 amps at 30v for 100w
but it might produce 15v and 1.6 amps at dawn while mine does nothing that is high enough to produce a charge from the controller, so the sun ARC, charge time is extended on both ends of the arc with higher voltage panels and mppt controller, it won't be in max mode at dawn, IN THIS EXAMPLE, at dawn it will be just passing power thru, but something would be happening, once the voltage passed the power point setting the DC converter mode would be activated and the excess voltage converted to amps, my panels have open circuit voltage of 23v and working voltage of 17.2 so at MAX output there is 3v to convert to amps instead of reducing the voltage as wasted heat in the controller, the older PWM technology, pulse the charge to try an use the voltage above 14v but it still wasted power to heat reducing the voltage, thats one of the reasons early panels were 15 or 16 volts, less waste in the controller, improved technologies allow for more voltage, MPPT uses that instead of wasting it. but you have to have clear skys and good sun angle to so the panels create that voltage and full power
also lower amps per watt produced means less voltage drop between panels and controller ( amps * wire Resistance = power lost )
so higher voltage panels get more power into the controller to be converted to amps out at the correct charge voltage
here is a QUOTE, an example using different numbers
from this web page power compare
the real gain of MPPT is with higher voltage panels, 20v's or more at the controller
example the 2000e can accept 30v input, batteries are charged at less than 1/2 , batteries are charged at 13.6 to 14.2v
30v panels would create 14v output "earlier in the day OR with bad weather" before my 17v panels do, so they would start charging sooner ( just a few amps into the controller ) before mine even start to have any usable output, then as the sun climbs and the voltage goes up the MPPT controller converts the excess higher voltage into amps
some controllers can take 70v input
any way a 100w panel at 17.2 volt produces 5.8amps max at 100 watts and 17.2v
a 100w panel at 30v would produce 3.333 amps at 30v for 100w
but it might produce 15v and 1.6 amps at dawn while mine does nothing that is high enough to produce a charge from the controller, so the sun ARC, charge time is extended on both ends of the arc with higher voltage panels and mppt controller, it won't be in max mode at dawn, IN THIS EXAMPLE, at dawn it will be just passing power thru, but something would be happening, once the voltage passed the power point setting the DC converter mode would be activated and the excess voltage converted to amps, my panels have open circuit voltage of 23v and working voltage of 17.2 so at MAX output there is 3v to convert to amps instead of reducing the voltage as wasted heat in the controller, the older PWM technology, pulse the charge to try an use the voltage above 14v but it still wasted power to heat reducing the voltage, thats one of the reasons early panels were 15 or 16 volts, less waste in the controller, improved technologies allow for more voltage, MPPT uses that instead of wasting it. but you have to have clear skys and good sun angle to so the panels create that voltage and full power
also lower amps per watt produced means less voltage drop between panels and controller ( amps * wire Resistance = power lost )
so higher voltage panels get more power into the controller to be converted to amps out at the correct charge voltage
here is a QUOTE, an example using different numbers
that’s where the DC/DC converter steps in. As a simple example, say you find that 2 panels in parallel give you 14.5V at 1.9A going through your non-MPPT charge controller, or 27.5W delivered to your batteries. Wired in series using MPPT they give you 37V at 1.25A or ~48W. You would get more power by wiring in series for a higher solar voltage of 37V, which is too high to charge a 12V lead acid storage battery. Now you need a MPPT.
The MPPT takes the 37V, 1.25A from your panels and gets ~48W, looses 2W in conversion inefficiencies(give or take) for 46W out, and converts it to 13.6V to charge your battery array at 3.38A whereas had you wired the two panels in parallel you would get about 27.5 watts in this illustration.
MPPT systems are found in high voltage solar arrays (100V+) because the peak power points in these systems are up high in voltage and low in current.
from this web page power compare
