sma sunny island grid feedback question

grgekeys

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Jul 8, 2021
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2
I recently bought one of those DC Solar auction trailers.

I've connected it to the house grid and enabled the back feed function where it feeds back extra energy from the solar panels not being used by the charger.

the problem is im only seeing half the power expected @about 1kW instead of the 2.5kW that's being generated by the panels.

does anyone know if there is a setting on the sma sunny islands that controls how much is fed into the grid?
 

Hedges

I See Electromagnetic Fields!
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Mar 28, 2020
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8,434
With DC coupled PV, if SCC charges battery higher than Sunny Island wants then Sunny Island will suck power from the battery and feed it to grid, of so enabled. Perhaps a higher target voltage on Midnight or lower on SI would deliver more.

Are you sure 2.5kW is being generated? Or can be? If it is generated, it is being consumed somewhere. If Midnight is moving off Vmp to reduce output because battery voltage is high enough, then there is an adjustment to be made somewhere. Maybe you're just having a bad production day due to haze, heat, angle? Ten 250W panels for 2500W STC aren't normally going to deliver a full 2.5 kW, but certainly more than 1kW.

A question no one has answered for me yet regarding these trailers ... Is there a battery shunt connected to Sunny Island so it knows how much current Midnight delivers? Or, is there a data cable from Sunny Island to a device MNSICOMM and from there to Midnight?


I don't know if SI is capable of grid export when it is capable of commanding Midnight.
 

grgekeys

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Jul 8, 2021
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yeah it's definitely producing roughly 2.5 at Times according to the midnite classic.

I've attached images of the classic and the two sunny islands, you can see the master reporting the power at 1.8 kW and the slave at .9kW it seems like the slave is the one doing the feed back into the grid.

20210710_124139.jpg
here's the master
20210710_124157.jpg
here's the slave20210710_124205.jpg
 

Hedges

I See Electromagnetic Fields!
Joined
Mar 28, 2020
Messages
8,434
I think that's one inverter sucking down -0.9 kW from grid and charging batteries, while other is pulling 1.8 kW from batteries to produce AC.

+1.8 kW - 0.9kW = +0.9 kW net AC production from battery.
2131W on Midnight - 900W consumed by SI = 1200W going into battery.

Both have a check mark next to grid connection. Suppose that means both connected.
I think they are set up for 120/240V split phase. Do you have both inputs fed from grid?

Master shows relay #2 closed? Probably default > 30% SoC, no need to shed load.


Does the trailer have a battery shunt, with sense lines to Sunny Island?
Does it have a data cable from Sunny Island to Midnight (probably through a small module to convert protocol)?
 
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