Solar in emergency

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olivernz

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#288962 3-Aug-2021 14:42

Hi all,

I've been trying my best to find the answer to this but don't seem to get anywhere really. So last hope here.

Generally when you have solar it shuts down when mains has a failure. And I totally understand why. Don't want to fry the poor chaps trying to restore power. The thing is, one of the reasons for Solar is, that if we have "the big one" (Wellington) and power will be out for days/weeks (and my solar array has survived) I want to be able to use my solar panels at least during the day to charge stuff and potentially have hot water/heating. Is there a way that (adheres to standards and) \I can take my home off the network and keep using solar? I'm thinking of a big as switch that needs to be manually switched or something.

I know that you can somehow circumvent the whole thing by installing a battery. I don't want that (yet) as it's a big expense and my excess solar will go into the EV anyway.

Has anyone done some digging on the topic? Or any suggestions who i could ask for an answer that won't just say NO?

Cheers

Oliver

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#2754537 3-Aug-2021 15:30

Sadly the answer is just ..... no

As you note it is a safety issue. No getting around it beyond a battery (I have Solar/Tesla Powerwall to pretty much live off-grid and have that backup). The below is not bad at explaining.

https://www.ausnetservices.com.au/-/media/Files/AusNet/New-Connections/Solar-Connections/Solar-Systems-and-Blackouts-Fact-sheet.ashx

olivernz

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#2754540 3-Aug-2021 15:44

Hmmm. Yeah that variable power makes some sense.

Beccara

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#2754543 3-Aug-2021 15:48

Transformers work both ways, feed 11kv in get 240v out AND feed 240 in get 11kv out which creates a hazard for anyone working on lines that "should" be dead in the event of a blackout. Now i'm not 100% up with current standards but if you got a non-grid tied inverter and a separate set of sockets you could plug things into in an emergency you wouldn't backfeeding the grid but I'm not 100% sure if the standards have caught up with multiple inverter setups

Most problems are the result of previous solutions...

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wellygary

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#2754547 3-Aug-2021 15:57

Beccara:

Transformers work both ways, feed 11kv in get 240v out AND feed 240 in get 11kv out which creates a hazard for anyone working on lines that "should" be dead in the event of a blackout. Now i'm not 100% up with current standards but if you got a non-grid tied inverter and a separate set of sockets you could plug things into in an emergency you wouldn't backfeeding the grid but I'm not 100% sure if the standards have caught up with multiple inverter setups

Yeah, that's pretty much the only way I could think of doing it,

You would need an isolation switch somewhere to sever the PV output from the regular household wiring and connect it to the dedicated "solar circuit"

olivernz

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#2754569 3-Aug-2021 16:36

That was the original idea. A relay that would take the house into off-grid mode. But as Quinny stated there's the added issue with having stable power without having a battery which I'll admit I ignored. I guess it depends what you're running there. If it's non critical stuff...but then in an emergency you do want the critical stuff.

So I guess you won't get round a battery. Just read EnPhase 8 micro inverters can do something re connected while mains is out but haven't fully understood what they are doing yet.

Wellingtondave

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#2754601 3-Aug-2021 17:29

Totally possible but it seems like it's slow to come to NZ, maybe there aren't the accredited / approved inverters here yet. Yes you do need a disconnect so you don't backfeed the grid when it's not live. You need to contact some solar companies / talk to your electrician.

From https://www.powershop.co.nz/solar-power/solar-power-systems/

"Hybrid inverter

If your solar power system has a battery in place for storage, the inverter manages sending power to the battery to be stored and used. Hybrid inverters have the advantage of being able to continue running off battery if mains power goes out. For this reason they have safety functions to completely disconnect from the grid, enabling the battery to continue powering the home. Talk to your solar power system providers about their inverter options and based on what you want to do with, make an informed decision on which unit is right for you."

Daynger

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#2754613 3-Aug-2021 18:10

Technically if you flipped your main switch off you are isolated from the grid, but more likely there would need to be a changeover switch installed as is done for backup generators.

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andrewNZ

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#2754615 3-Aug-2021 18:13

Any system without a battery, no.

A regular grid tied system with a battery, no. Although, I feel like there could be a way if you had a grid tied battery system and a separate isolated inverter direct off the batteries.

You'd have to look into it a lot more though.

Edit to add. Grid tie inverters are not allowed to operate if they lose the supply. And before someone says, backfeed the inverter with another inverter or ups, those items strongly object to the treatment...

eonsim

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#2754844 3-Aug-2021 23:29

Some of the grid-tie inverters have an emergency powerplug that allows you to plug a device directly into the inverter during a black out. See Fronius GEN24 as an example, they can provide up to 3kw through that plug. Won't allow you to run the full house but can probably keep the Fridge and a few devices going for a few hours.

Zeon

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#2754853 4-Aug-2021 00:52

Apparently in the US where more people have generators people back feed their mains wiring just through a regular power socket. Not sure if the circuit breakers will work well in reverse but if you could isolate the main wiring from the utility then I guess it could work as long as your inverter is running? Not sure how stable your power would be just on solar though? Would probably keep every load off you can think of except fridge etc..

In terms of charging your EV, I was actually thinking about this. Most EVs with AC charging will try and pull whatever they are rated for which could overload your measley solar supply pretty easily. If you used CHAdeMO perhaps you could use a boost converter to get your voltage high enough and feed the battery as best you can? Not very knowledgeable on this sorry but maybe worth doing some investigation?

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neb

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#2755109 4-Aug-2021 15:45

Zeon:
Apparently in the US where more people have generators people back feed their mains wiring just through a regular power socket.

US electrical regs allow things that are illegal (due to being too dangerous) in the rest of the world, so they're not a particularly good example of good practice... I was also surprised how many people in the US have generators, even in big cities like LA. The only place I've seen a similar acceptance that you need to keep a generator handy because the power is so flaky is Africa.

olivernz

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#2755134 4-Aug-2021 16:24

So looks like EnPhase micro inverters IQ8 have the ability to stay up in a power failure even without a battery. Now don't ask me how. Still searching for exact details but there is a cut off relay involved. Also the IQ8 inverter is scheduled for late this year early next year at best.

Scott3

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#2755310 4-Aug-2021 22:18

eonsim:

Some of the grid-tie inverters have an emergency powerplug that allows you to plug a device directly into the inverter during a black out. See Fronius GEN24 as an example, they can provide up to 3kw through that plug. Won't allow you to run the full house but can probably keep the Fridge and a few devices going for a few hours.

Not sure if they offer a 230v 50hz version, but some sunny boy inverters have a feature called "Secure Power Supply" which does the same thing. Essentially a dedicated outlet that you can plug things into in daylight hours during a power outage.

Dedicated outlet gets around the issues of needing a switch to isolate the grid etc. Obviously a bit or a chore to run an extension cord to your fridge etc.

I don't know if there is anything to stop your sparky installing a generator transfer switch (essentially a big input switch that allows the house to be fed by the grid OR a generator, but not both), and either wiring the emergency output directly to the switch, or providing a cord that can connect it to the input connector (is it still called a socket if it is male?)

Of course the power available is going to be pretty limited, don't know if it would be able to start say a vacuum cleaner motor.

Scott3

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#2755314 4-Aug-2021 22:30

Zeon:

Apparently in the US where more people have generators people back feed their mains wiring just through a regular power socket. Not sure if the circuit breakers will work well in reverse but if you could isolate the main wiring from the utility then I guess it could work as long as your inverter is running? Not sure how stable your power would be just on solar though? Would probably keep every load off you can think of except fridge etc..

In terms of charging your EV, I was actually thinking about this. Most EVs with AC charging will try and pull whatever they are rated for which could overload your measley solar supply pretty easily. If you used CHAdeMO perhaps you could use a boost converter to get your voltage high enough and feed the battery as best you can? Not very knowledgeable on this sorry but maybe worth doing some investigation?

back feeding with a suicide cable isn't a great idea.... The nick name of the double ended male cable you need to do this is a strong hint alone. Not that NZ power with 230v phase to neutral is a bit more dangerous than US power (two phases, each opposite each other and 110v above neutural (and 220v apart form each other).

Regarding EV charging current, EV charge cords have two skinny signal wires that provide a signal to the EV as to how much power it can draw from the supply. My leaf is capiable of drawing 16A, but I have a cord with a normal 10A plug on it, that is that allows charge currents of 8A or 6A to be selected (NZ guidelines only allow drawing the full 10A from a normal socket if the plug has temperature monitoring). Most EV owners have some kind of cord that allows them to charge from a domestic socket, and many EV's allow the charge current to be tweaked from the dash (not my leaf, but the i3 i used to have could do that).

Directly charging the pack (cira 360V) DC is technically feasible, but a pritty epic project (dangerous too). Much easier to just feed it 230v via a cord that sends a signal calling for a 6A or 8A draw and use the onboard charger.

boland

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#2755542 5-Aug-2021 11:03

Scott3:

eonsim:

Some of the grid-tie inverters have an emergency powerplug that allows you to plug a device directly into the inverter during a black out. See Fronius GEN24 as an example, they can provide up to 3kw through that plug. Won't allow you to run the full house but can probably keep the Fridge and a few devices going for a few hours.

Not sure if they offer a 230v 50hz version, but some sunny boy inverters have a feature called "Secure Power Supply" which does the same thing. Essentially a dedicated outlet that you can plug things into in daylight hours during a power outage.

Dedicated outlet gets around the issues of needing a switch to isolate the grid etc. Obviously a bit or a chore to run an extension cord to your fridge etc.

I don't know if there is anything to stop your sparky installing a generator transfer switch (essentially a big input switch that allows the house to be fed by the grid OR a generator, but not both), and either wiring the emergency output directly to the switch, or providing a cord that can connect it to the input connector (is it still called a socket if it is male?)

Of course the power available is going to be pretty limited, don't know if it would be able to start say a vacuum cleaner motor.

I've got a Sunny Boy inverter and have done a lot of research about this as well. Unfortunately, the SPS is US only.

The only solution in NZ as far as I can tell is to get a battery. Have requested quotes from multiple suppliers, and it's not cheap. It's cheaper to just buy a generator...

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