3.3 KW off Grid System

Barbar0ssa

Solar Enthusiast
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Mar 3, 2021
Messages
77
I pulled all 4 input strings and measured them. 94v, 94v, 30v, 3v. So 2 strings are worse than useless at the moment and I probably need to get back on the roof to debug them. I guess that is good news because that means there is some hope for improvement in the future. I left only the 2 performing strings connected.

My latitude is 41.079639. And I think my calculator for my sub-optimal angle and direction (~45, pointed 265 degrees West) mislead me so my best case scenario is probably not as good as I had hoped.

The MPPT range of my SCC is supposed to be 60v - 120v, but soon after connecting the strings (closing breaker), the voltage drops all the way to 54v or 55v on the meter. Before I close the breaker, the panel output is 94v and the solar input terminals on the SCC are battery voltage (53-54v).When the breaker closes, I watch the voltage slowly work it's way down. Is this the expected behavior for MPPT?
 
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Supervstech

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I pulled all 4 input strings and measured them. 94v, 94v, 30v, 3v. So 2 strings are worse than useless at the moment and I probably need to get back on the roof to debug them. I guess that is good news because that means there is some hope for improvement in the future. I left only the 2 performing strings connected.

My latitude is 41.079639. And I think my calculator for my sub-optimal angle and direction (~45, pointed 265 degrees West) mislead me so my best case scenario is probably not as good as I had hoped.

The MPPT range of my SCC is supposed to be 60v - 120v, but soon after connecting the strings (closing breaker), the voltage drops all the way to 54v or 55v on the meter. Before I close the breaker, the panel output is 94v and the solar input terminals on the SCC are battery voltage (53-54v).When the breaker closes, I watch the voltage slowly work it's way down. Is this the expected behavior for MPPT?
Yes, especially in low angle weak sun combined with low outdoor temps.
 

chrisski

Photon Sorcerer
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Aug 14, 2020
Messages
2,365
Yes, especially in low angle weak sun combined with low outdoor temps.
I only deal with three 100 watt panels in series, but that would not be normal tome.

I would expect voltage to drop from open circuit voltage to working voltage, whatever the panel sticker says, but 10-15% is what I expect. Maybe a little more, but not that much.

The OP is getting 40% which in my limited experience is too much for sunny panels,but in cloudy and partly shaded panelsvoltage can drop40% or more and not be bad.
 

Barbar0ssa

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Mar 3, 2021
Messages
77
I took off the MC4 connector of one of the two strings producing nothing. When I unscrewed and then tugged on it, the connector came off but the crimped piece let go of the wire and stayed in the plastic. 😭 I am fairly certain I have some bad connections on the roof. This is infuriating because the connectors were highly reviewed and everything crimped positively and withstood a vigorous tug while assembling.

So, until I am willing to rent another cherry-picker, I have a 4 panel 1800w solar system. The wife is incredibly sick of this system so it may be a while. This system usually produces ~850w in the glancing sun though I have seen it spike briefly to 1700w.

It looks like I am averaging 3kwh a day coming in (according to the inverter app) with less than half of that going to the batteries for some reason. I might need to get a shunt on there to try and make sense of what the battery is seeing beyond the data from the BMS app.

As far as the voltage for MPPT, I did see it sitting at 79v yesterday afternoon so it is not always dropping so close to battery voltage. It seems like it is working, if only at 1/4 of design capacity.

Lessons learned:

1. Calculators may underestimate power production for sub-optimal angles/direction.
2. Test Test Test before returning the heavy equipment no matter how exhausted you are.
 
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chrisski

Photon Sorcerer
Joined
Aug 14, 2020
Messages
2,365
For me, if I have large loads on Ike the microwave, the amps produced by the panel go into the inverter,but do not pass through the battery shunt.

My Microwave takes 155 amps, and my panels can produce 74 amps, so the battery shunt only pulls out 81 amps from the batteries.

Some thing when other loads kick on, if I’m seeing the panels push 60 amps with no loads, I will see 60 amp on the battery shunt, but when the 9 amp propane heater blower motor kicks on, amps to the battery drops to 51, but amps from the SCC remain 60.
 
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