MPP LV6548 and SMA Sunny Boy Grid Tie?

Hedges

I See Electromagnetic Fields!
Joined
Mar 28, 2020
Messages
8,434
"Today not even a small solar panel is connected to OffG inverter. Not needed."

Moving some PV panels to it will let it run longer during grid failures. Too much PV, and available power goes to waste because you're not using it for loads at that time.

If you rig up a way to switch over some panels during a power failure it can remain up longer.
I would get a switch rated for Voc of the PV string (e.g. a 600VDC heavy-duty disconnect) and use that to open the GT PV string.
Then inside the box, have pluggable connectors (e.g. MC4 with retaining clips cut off), bundled so suitable groups of panels either connect in series for GT inverter, or connect in parallel (if required for lower Voc limits) to MPP.
A 3PST switch might serve to connect up to 3 strings to the MPP, so no current flowing while mating connectors. Once box is closed up again, throwing the switch connects the strings.
 

mrzed001

Voice of reason
Joined
Apr 10, 2020
Messages
721
Location
Hungary - EU
"Today not even a small solar panel is connected to OffG inverter. Not needed."

Moving some PV panels to it will let it run longer during grid failures. Too much PV, and available power goes to waste because you're not using it for loads at that time.

If you rig up a way to switch over some panels during a power failure it can remain up longer.
I would get a switch rated for Voc of the PV string (e.g. a 600VDC heavy-duty disconnect) and use that to open the GT PV string.
Then inside the box, have pluggable connectors (e.g. MC4 with retaining clips cut off), bundled so suitable groups of panels either connect in series for GT inverter, or connect in parallel (if required for lower Voc limits) to MPP.
A 3PST switch might serve to connect up to 3 strings to the MPP, so no current flowing while mating connectors. Once box is closed up again, throwing the switch connects the strings.

The battery is 14,4 kWh. The house needs 10-12 kWh/day (with electric oven and cooktop). So I am not afraid of a little blackout :D
I was thinking of a switch for PV. Even to switch 4kW of the array, buy a 5048MGX inverter and that has a 500Vdc MPPT (connect to the same battery, so DC coupled)
But then I choose the SolarEdge inverter for GT (shading) and this blocked everything (SE optimizer for all panels).
So in a BIG blackout I have to manually disengage the SE optimizers. It is not ideal, but maybe (I hope) I never need it.
Also I can separate everything from the grid, and with a little 1kW inverter produce sine wave to start GT ... I know it is risky, but with care (and constant loads like a heaters) it can work.
 

Sanwizard

Photon Sorcerer
Joined
Feb 2, 2021
Messages
1,302
The battery is 14,4 kWh. The house needs 10-12 kWh/day (with electric oven and cooktop). So I am not afraid of a little blackout :D
I was thinking of a switch for PV. Even to switch 4kW of the array, buy a 5048MGX inverter and that has a 500Vdc MPPT (connect to the same battery, so DC coupled)
But then I choose the SolarEdge inverter for GT (shading) and this blocked everything (SE optimizer for all panels).
So in a BIG blackout I have to manually disengage the SE optimizers. It is not ideal, but maybe (I hope) I never need it.
Also I can separate everything from the grid, and with a little 1kW inverter produce sine wave to start GT ... I know it is risky, but with care (and constant loads like a heaters) it can work.
Quick update. Putting up solar panels on an almost vertical roof by yourself sucks, but I finally got it done. The wife balked at my ground mount idea, as she didnt want panels in the yard, so I dropped the count from 16 to 12, and am feeding ea
ch LV6548 with a 6S string 240V. (Each PV input on an LV6548 can handle 250V). So that leaves 2 x 4000w PV inputs available if needed.
I have been wondering how much this all would have cost if I had it done professionally. I imagine just buying the mounts and installing the panels, then wiring everything to the combiner box, grounds, lightning protection alone would cost a lot. Then there is 26KW of Lifepo4 battery (probably $10,000 for the batteries alone? How much is a commercial 26KW Lifepo4 battery? )
Then 13KW of inverter power, and all the DC and AC wiring including transfer switch, load panel, etc in electrician costs.
Has anyone ever figured out how much you saved by using this forum to DIY a system like this? Will should run the numbers. Probably a cool exercise to show value and return on investment for this hobby.
 

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