PV Switch

dmholmes

Solar Enthusiast
Would a residential installer do a grid tied system with a manual switch before the string inverter to route the PV DC to a separate MPPT/battery system for outages?
 

crossy

Solar Enthusiast
Make very sure you use DC switches/breakers of the correct voltage rating.

I would be more concerned how you connect your now off-grid system to your home safely.
 

Hedges

Photon Sorcerer
If there were approved plans and permit, shouldn't be a big issue but they would have to carefully examine the plans.
Getting someone to design it and create plans would be the difficulty.

Under 125 Voc, I think I could accomplish that with a pair of interlocked Square D QO branch circuit breakers.

Higher voltage, you need a suitably rated transfer switch. Disconnect switches are easier to come by. The UL listed transfer switches I know of will cost more than the PV panels they disconnect (!) i.e. cheaper just buy more panels.

My redneck engineering approach would be a suitably rated disconnect (with cover that can only be opened when off), and touch-safe connectors inside.

Best approach is make your MPPT/battery system grid tied and assign some panels to it.
 

dmholmes

Solar Enthusiast
If there were approved plans and permit, shouldn't be a big issue but they would have to carefully examine the plans.
Getting someone to design it and create plans would be the difficulty.

Under 125 Voc, I think I could accomplish that with a pair of interlocked Square D QO branch circuit breakers.

Higher voltage, you need a suitably rated transfer switch. Disconnect switches are easier to come by. The UL listed transfer switches I know of will cost more than the PV panels they disconnect (!) i.e. cheaper just buy more panels.

My redneck engineering approach would be a suitably rated disconnect (with cover that can only be opened when off), and touch-safe connectors inside.

Best approach is make your MPPT/battery system grid tied and assign some panels to it.
Our plan currently is to go with a Tesla installation, but somebody in the FB Bluetti group posed this question which piqued my interest. She was asking if she could use a 4 kW grid-tied installation, 2 strings of 2 kW, and divert each of the strings from the grid-tied inverter to a AC300 (2,400 kW PV input each).
 

Hedges

Photon Sorcerer
Haven't found PV input voltage for AC300, but likely different from GT inverters so need to segment PV string and rearrange series/parallel.

I could figure out a way to do it (with a bunch of connectors) but not something for everybody to do. Ideally ganged connectors so just move one group between two others, but depending on voltage I might use individual MC paired up with cable ties or heatshrink.
 

Hedges

Photon Sorcerer
If GT PV inverter has 600V string, need to segment in four.

I would run the PV string through a 600VDC switch to interrupt current (best to switch off at AC breaker anyway).
Assuming that switch is 3PST, only 3 substrings can be swapped, with switch keeping them open-circuit until it is turned back on. The fourth substring would remain connected to GT PV inverter and not be used.

Inside the switch box (interlocked lid won't open when turned on), I would have three pairs of MC connectors wired to three 150V max segments of PV. three pairs wired in parallel to AC300. three pairs wired in series to GT inverter. While switch is off, unplug from one and plug into other.

I would use MC3 connectors which have no lock, or cut the locks off MC4 connectors. Unless some other connector is touch-safe and rated for 600V.

If you don't have either GT inverter or all-in-one, you could get a grid-backup system instead of swapping PV connections.
Tesla with Powerwall.
SMA Sunny Boy/Sunny Boy storage
Sunny Boy/Sunny Island
Sol-Ark
MPP
Outback Skybox
several others.


Some use 400V batteries. Some 48V. In some cases, batteries optional.

If you get a GT PV inverter that does frequency-watts, you can add a battery inverter later which performs frequency shift control.
 
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