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Not sure if covered here but toying with idea of using a switch or (latching) relay to turn an AC panel into a DC panel by inserting DPDT switch or relay between panel o/p (DC) and microinverter input. Wiring would be such that the switched from (not sure if there's a tech term for these contacts? Common?) would be from the DC panel and the switched to #1 would be to microinverter (grid tie) and switched to #2 would be to a solar charge controller to feed a battery bank/inverter/etc. Purpose of this set up would be so that otherwise "dead" AC panels could be used in a grid down scenario. I'm pretty sure I know how to wire up to charge controller (panel parallel/serial, wire size, runs, etc) but curious if anyone has taken this approach. Or propose a different. Latching impulse relay(s) could be controlled from inside house and pretty quick switchover. Primarily thinking of just a fraction of the panels set up this way to have maybe 2-3 kWh/day utilization so as to not $$$$ with gobs of batteries/inverter size/etc. Basically, utilize this as backup power vs. a gas generator. It seems like this could/should be offered by installers of AC panels (even if only wired this way without the rest of the hunks and pieces).
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If the microinverter is not functioning, it's unlikely to need to be "isolated" with a DPDT switch. Just wire into the DC and use it. All the precautions, fuses, proper gauge wire still apply
Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A
solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-Lister -
Point is if grid is down the AC panels won't work. All of the microinverters are fine but they need the 60 Hz from grid to work. This is actually for my in-laws as my mother in law has been pleading for a backup generator for years. They used up their entire lot with home rebuild several years ago so can't place a genie anywhere because of setback/aesthetic requirements. I'm trying to set up a dual-purpose use of their existing AC grid-tied panels. Flip a switch (or relay) and the DC from panel fed to an off-grid system. Pretty sure there's no design issue, per se, just looking to see if any one else has done this or may have a better idea. Father in law talking about wanting 10 kWh of battery storage. Figure one panel to keep batteries charged and about 7 (350W/panel) to keep them up and running in extended grid down situation. They have 20 panels.Comment
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How do you plan to connect DC wiring to the 20 panels and also have the microinveters connected? If you want batteries then wouldn't an AC coupled home battery be simpler?
Hard to imagine a home with space for 10kwh batteries but not for a generator. What size generator are you looking at? Portable generators can be pretty small.Last edited by solardreamer; 02-23-2022, 12:21 AM.Comment
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Two batteries:
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7 of the 20 panels to service (i.e. keep charged in grid down situation) these two batteries. Use a double pole double throw switch or relay (pls read my original post) on the 7 panels (between DC panel and uinverter). They (my in-laws) were thinking like the Generac systems you can see on tv commercials. They have to run outside for exhaust. LiFePo4 can be operated inside. BTW, didn't intend to post a huge pic!!
Their currently installed system runs fine. Just looking for a clever way to get a backup power system for them.
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Current configuration is 20 panels with microinverters. The panels consist of a DC PV panel and a microinverter. One each. Direct grid tie as the microinverters output 220 VAC. These panels will only work with the grid up by design (lineman safety, etc). What I was thinking of doing is putting a DPDT switch (or relay) on 7 of them ("normal" grid tied usage in one switch position and in other switch position just use the DC output from the panel itself...as in cut both wires between the DC panel and the microinverter and insert one switch per panel. Then DC lines go to a MPPT charge controller/batteries/inverter/etc. Essentially now an off grid system utilize a transfer switch at the electrical panel if/when grid down. This being a way to utilize existing panels for an emergency back up system.
So no...to running to microinverters (already have that). And no to AC coupling because the panels will not generate power in a grid down scenario. Mostly just spitballing here because in law has room for additional panels on roof and that's a much simpler approach and really only extra costs would be panels as need for all other elements (batteries/charge controller/inverter/etc). would still be there. Figure at most 2000 W of new DC panels.Comment
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Switching serious DC is not a trivial problem. I never mess with panel wiring
when it is not dark. Bruce RoeComment
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So you want to insert the DPDT's between the panels and micros on the roof? Not sure where you are located but that could be a pretty harsh environment for typical DPDT's to operate long term. Also, not sure you really need the DPDT's since you plan to have a switch panel. Seems like you could just use splitter connectors between the panels and micros.
You have incorrect understanding of AC coupled home battery systems. They use specialized inverters (e.g. Schneider Conext, etc.) that activate and control power from grid-tied inverters during grid outages.
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Thx Solardreamer...Will look further into AC coupled. Especially like the idea of just doing all at the electrical panel and leaving the current installation alone. Also would have all of the panel power available vs. just the 7 or so I was thinking of.
SoCal location so installing at panels in specialty metal box would probably be ok if that route taken but do like the idea of switching inside house. Would require two pairs of wires for each panel but could probably be 14 Gauge. (~60 V @ ~ 7 Amps).Comment
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BTW Bruce...I worked with 6 - 20 kV DC in my younger days. Got bit a couple of times...not fun. Also heard a zap and was first to discover a coworker on the ground (alive) and yet smoke coming off of her body. This in a test lab....not up on an AC pole. I'm really confident in my "don't get bit" skills these days...had a chuckle w/your comment!Comment
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Yes safety matters too. But my comment was relative to hardware needed
for making and breaking DC circuits. A contact on DC can draw quite an arc,
which an AC duty switch is not set up to deal with. Even my array test light
draws a nice, current limited arc.
If shutdown was needed, I would open the AC inverter output first, with
the DC current stopped, circuits would arc less. Bruce Roe
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