Watts needed
I have read where folks suggest any where from 1 to 2 watts of solar per ah of battery. My question, is this based on battery rating (ie 215 AH) or is it based on useable amp hours(105)? All reply...
Forum Discussion
Two 285s in series will add their voltages so the controller does need about 80v for the total Voc so yes, 100Voc input would be right.
A 20 amper will just run what one of those 285s can do, so at least a 40 amper would be needed. I would choose a 40 instead of going to a 60 because the panels will get hot in the sun and be about 10% down in watts from that heating, so that keeps you under what a 40 can do. Also if mounted flat they will not get full sun, so that keeps the watts down too.
Tracer makes a decent 40 amp MPPT that would do at a good price. Lots of other choices with various features and prices.
MPPT uses output watts / battery voltage for amps out (which go to loads first and any left over go to the battery)
2 x 285 = 570w less 10% for heat = 513w minus say 2% wiring loss panels to controller, so now 503w input to the controller. controller efficiency maybe 96% so output watts = 483w so picking three battery voltages:
483/12 = 40.25 amps
483/13 = 37 amps
483/14= 34.5 amps
As you see, you get more amps to the battery when the battery is low. However you get more watts into the controller at mid-day high sun. but by then the battery is higher in voltage, so you likely never see the set--up doing all it could do. for that you would need to aim the panels at the sun at high noon and have the battery voltage down low.
Solar gets the job done though, so expect to be pleased you got it.
A 20 amper will just run what one of those 285s can do, so at least a 40 amper would be needed. I would choose a 40 instead of going to a 60 because the panels will get hot in the sun and be about 10% down in watts from that heating, so that keeps you under what a 40 can do. Also if mounted flat they will not get full sun, so that keeps the watts down too.
Tracer makes a decent 40 amp MPPT that would do at a good price. Lots of other choices with various features and prices.
MPPT uses output watts / battery voltage for amps out (which go to loads first and any left over go to the battery)
2 x 285 = 570w less 10% for heat = 513w minus say 2% wiring loss panels to controller, so now 503w input to the controller. controller efficiency maybe 96% so output watts = 483w so picking three battery voltages:
483/12 = 40.25 amps
483/13 = 37 amps
483/14= 34.5 amps
As you see, you get more amps to the battery when the battery is low. However you get more watts into the controller at mid-day high sun. but by then the battery is higher in voltage, so you likely never see the set--up doing all it could do. for that you would need to aim the panels at the sun at high noon and have the battery voltage down low.
Solar gets the job done though, so expect to be pleased you got it.
