Feasible to use 3 panels instead of 2 or 4? 48 volt system.

softdown

Say “45 volt” panels. Currently I only see 45 volt output or 135 volt output when employing three 50 volt panels. 

When does voltage become significantly “inefficient” for a 48 volt system?  135 volts too much? 

littleharbor2

That all depends on charge controller type and voltage range some of the charge controllers in the all-in-one inverters wouldn't even accept 135 volts is being too low so we need to know what charge controller you're using

softdown

Considering this one:

POWLAND 80A MPPT Solar Charge Controller,12V/24V/36V/48V Auto,Max Input 150V LCD Display

Almost no way the very inexpensive, light weight charge controllers are going to last for years and years. But I only need additional solar for 2 months out of the year right now. I need to pare down my freezing and refrigeration demands. Takes a long time to empty a freezer.

littleharbor2

At 135 volts open circuit you getting dangerously close to the Charge controllers maximum limit so if you have cold cold weather where you are I wouldn't recommend three in series but why don't you go 2s2p, two in series twice with  your four panels

softdown

littleharbor2 said:

At 135 volts open circuit you getting dangerously close to the Charge controllers maximum limit so if you have cold cold weather where you are I wouldn't recommend three in series but why don't you go 2s2p, two in series twice with  your four panels

40 volt panels so margin of safety.
No room for 4 panels due to roof adjoining sunroom.

littleharbor2

45 volts open circuit* 3 equals 135 volts at 75° F you put those in cold temperatures like you were talking (-21 f) about they're going to burn up your charge controller

softdown

I was guessing at the 45 volts. I have 35 and 40 volt panels. Assumed that the larger panels would be higher voltage. They are lower voltage. 

I said 40 volts on Aug. 9th post. 

BB.

With electrical/electronics... "No Guessing"!

-Bill 

softdown

Good point. I’m trying to schedule knee surgery. Climbing ladders can be onerous. Made sense, to me, that panels that are 25% larger would be higher voltage. A clear mistake in retrospect. 

Now I don’t think there is any way to approximate panel specifics without looking at the information label on the back. Which the sun may have eroded fwiw.