We have solar without batteries - cheap way to have power during an outage

Forums › Home Workshop DIY › We have solar without batteries - cheap way to have power during an outage

boland

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#315801 17-Aug-2024 10:42

We have solar panels with a Sunny Boy inverter, without a battery. It seems the costs for home batteries are not coming down, a 13.5kWh Powerwall still costs $17k.
While it's possible to save some money with a home battery it's not a good ROI.

I'm now looking into cheaper options. We don't want a petrol generator, but based on this topic I have an idea.

Get 1 or 2 12V 100A deep cycle batteries
12V to 220V inverter
Transfer switch kit installed in the house by a sparky
Then, during an outage, I'd plug in the 220v inverter into the transfer switch kit.
This would fire up the solar inverter and then most of the power would come from the solar panels.
Get a 12v battery charger to keep the deep cycle battery topped up.

So the 12v batteries would just be a buffer and a kick starter for the inverter, plus they would keep the fridge on when there's no sun. It probably won't be enough to last through a night, but that's fine.

Would this be possible? There is a loop (sorry if that's not the right word) as the 12v batteries both power the house but are also being charged from the house. There's a 12v => 220v inverter in between, but not sure if that would be an issue?

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#3272813 17-Aug-2024 11:18

Solar inverters will not sync with things that are not a grid. I know people who have tried it with some not quite legit in NZ grid tie inverter on their caravan that would invert fine when on wall power, but when on a generator or inverter they would just flash up error. It was not a matter of the grounding because that error would come up straight away when it was powered on if there was no neutral to earth link on the incoming supply.

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boland

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#3272818 17-Aug-2024 11:24

richms:

Solar inverters will not sync with things that are not a grid. I know people who have tried it with some not quite legit in NZ grid tie inverter on their caravan that would invert fine when on wall power, but when on a generator or inverter they would just flash up error. It was not a matter of the grounding because that error would come up straight away when it was powered on if there was no neutral to earth link on the incoming supply.

Thanks. But how does it work when we'd have eg a Powerwall? We've been told that then the solar inverter would work as usual and keep the lights on & Powerwall charged.

richms

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#3272830 17-Aug-2024 11:46

boland:

Thanks. But how does it work when we'd have eg a Powerwall? We've been told that then the solar inverter would work as usual and keep the lights on & Powerwall charged.

Those inverters in powerwalls etc are designed to support bidirectionality on them. Otherwise if you have an inverter that doesnt support that, the solar inverter will have nothing taking its power when the load doesnt like at the lower parts of the AC wave for most non resistive loads.

There are plenty of grid tie inverters on aliex that you can get and have a play with, but they are technically a prohibited item here, so I don't know if customs are out to get them like they are with baofengs and other walkietalkies.

Richard rich.ms

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#3272831 17-Aug-2024 11:47

boland:

richms:

Solar inverters will not sync with things that are not a grid. I know people who have tried it with some not quite legit in NZ grid tie inverter on their caravan that would invert fine when on wall power, but when on a generator or inverter they would just flash up error. It was not a matter of the grounding because that error would come up straight away when it was powered on if there was no neutral to earth link on the incoming supply.

Thanks. But how does it work when we'd have eg a Powerwall? We've been told that then the solar inverter would work as usual and keep the lights on & Powerwall charged.

i believe it's because It's able to generate the grid frequency to keep the inverter running. it also has an automatic disconnect for the grid.

A regular inverter like you mention while generating 50hz does so pretty poorly.

larknz

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#3272940 17-Aug-2024 16:49

Most solar inverters are designed to shut down in the event of a network power outage to avoid electrocuting any workers working on the network. This is a requirement of the standard they must comply with.

neb

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#3272959 17-Aug-2024 17:59

richms: Solar inverters will not sync with things that are not a grid.

Well, in theory if you've got a grid-forming inverter you're OK, but they're generally utility-scale devices and I can't imagine how many regulations you'd violate if you connected one of those up here.

Overall though as you point out, the amount of not-very-legit custom plumbing the OP would have to install, and the fact that it's unlikely that anyone qualified will want to sign off on it, doesn't really make it worthwhile. You really need something that ties the inverter and batteries to an ATS (automatic transfer switch) that safely isolates the grid from the house power during an outage, and for that you really can't go down the DIY route if you want it to be above-board.

raytaylor

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#3273024 17-Aug-2024 20:10

I dont know much about your inverter or its capabilities but I would go with...

1) Get a 240v AS/NZS 3112 and transfer switch input installed on your breaker board.
You can use this to supply your house from a generator or electric vehicle.
This gives you the most flexibility in model of generator, inverter or car type but does limit you to 10 amps / 2kw or your inverter output if lower.

Flexibility is key - eg. a car with a 240v output and a range of 200kms will run the basic appliances for over a week.

2) Get some deep cycle lead acid batteries with an inverter, a standard 30 amp solar controller and have a transfer switch installed on the solar panel wiring.

When you throw the switch, only a few of the solar panels (max 30amps 100v) are connected to the mini solar controller to charge up the batteries and run the inverter.

We were without power for a week in Napier after cyclone gabrielle.
I rigged up some solar panels to some batteries and an inverter so we were able to power most things silently in the house (fridge, tv, router, lamps, phone chargers) without the noise of a generator.

Only needed to start the generator to run the microwave

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SomeoneSomewhere

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#3273041 18-Aug-2024 01:16

I believe in general the battery inverter/BMS either needs to communicate with the PV inverter (compatible brands, cables), or the battery is connected via the DC bus in the inverter.

I don't think any of the systems are approved to just have the battery pretend to be the grid with the PV inverter not knowing the difference - at minimum, things will fall apart once the battery is full and stops accepting current.

You might get marginal results if you had CTs and the grid-tie inverter configured not to export, but I suspect even that is optimistic. At minimum you'd want more kVA in the battery inverter than the grid-tie inverter and that's not going to happen in a cheap setup.

One of the standards, either generating sets or the PV standards, explicitly says that your transfer switches can't be set up so that a grid-tie inverter can be connected to an off-grid supply.

raytaylor:

2) Get some deep cycle lead acid batteries with an inverter, a standard 30 amp solar controller and have a transfer switch installed on the solar panel wiring.

When you throw the switch, only a few of the solar panels (max 30amps 100v) are connected to the mini solar controller to charge up the batteries and run the inverter.

We were without power for a week in Napier after cyclone gabrielle.
I rigged up some solar panels to some batteries and an inverter so we were able to power most things silently in the house (fridge, tv, router, lamps, phone chargers) without the noise of a generator.

Only needed to start the generator to run the microwave

This is a reasonable option, but proper 600VDC rated isolating switches don't come cheap, especially when you're trying to find versions that can be interlocked. If your system relies on people switching things in the right order, sooner or later someone will operate a switch in the wrong order, and find out that the switch can't break DC loads. That's not a pretty situation.

chimera

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#3273125 18-Aug-2024 09:27

A single 12V 100A battery is way too small, you won’t even boil the jug with that.

SomeoneSomewhere

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#3273233 18-Aug-2024 14:10

Boiling a kettle is actualy a pretty large demand.

Still, it should be pretty achievable: that's 1.2kWh and the kettle needs 2.5kW for about 5 minutes. You're doing about 2C; much better than most UPSs.

Regardless, what OP wants seems to be just as much power as the solar can deliver while the sun is shining.

michaelmurfy

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#3273248 18-Aug-2024 15:56

For the odd time you need to power things in an outage how about looking at upgrading your car to an EV with vehicle to load capability (like any of the MG’s, BYD’s or even the Kia’s).

Then you get a new vehicle you can charge from your solar and a 60kwh battery you can use during power outages to power essentials. These can normally supply a good chunk from V2L to power things like your fridge / freezer, jug, air fryer, TV and router etc.

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boland

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#3273268 18-Aug-2024 17:04

michaelmurfy:

For the odd time you need to power things in an outage how about looking at upgrading your car to an EV with vehicle to load capability (like any of the MG’s, BYD’s or even the Kia’s).

Then you get a new vehicle you can charge from your solar and a 60kwh battery you can use during power outages to power essentials. These can normally supply a good chunk from V2L to power things like your fridge / freezer, jug, air fryer, TV and router etc.

Thanks, yeah, also had a look. I'm not a fan of MG based on many different stories regarding build quality and safety. They are depreciating very quickly.
BYD maybe, but they are still ~$30k+. Same for Kia Niro. But I guess EV prices will keep coming down.

In terms of kWh and dollar value, it's so strange that a 13.5kWh Powerwall costs $17k but for a bit more I can get a whole car around it with 4 times the battery size.
That's why I don't want to buy a PW.

boland

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#3273271 18-Aug-2024 17:12

Thanks all for the replies. I guess my original solution is not going to work.

I did the maths on a Powerwall and we'd save about $500 a year, assuming we can charge it at night / with sun during the day for cheaper rates and thus avoid peak rates.
Not financially worthwhile.

Probably our best bet is to get an EV with V2L and optionally a transfer switch in our house.

It's still strange there isn't a cheaper home battery solution. We'd only need a ~6kWh battery for the basics. I believe only the Powerwall can be installed without inverter, all the other battery solutions require an inverter.

I'm happy to pay more than my original solution, up to around $9k, for a decent, approved solution. Definitely not looking for a not-so-legal solution.

chimera

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#3273276 18-Aug-2024 17:35

I’ve bought 15kwh for about NZ$4300 landed, it’s on a ship from China, yet to arrive. Will let you know once it’s setup and let you know my thoughts. PM me direct if you want to know what I got (have done endless research) Bear in mind they are for a hybrid inverter, so if you are just grid connected only and doing separate battery inverter YMMV.

EDIT: I should elaborate on my post, I’ve done a heap of research and found a very good quality compliant enclosure with BMS and batteries to run here, and am 99% sure they will be all good, but don’t want to post publicly until they arrive, everythings setup, with solar installed and everything signed off first. You could upgrade your inverter and get the batteries for less than your $9k budget. PM if you wanna know what I got.

michaelmurfy

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#3273289 18-Aug-2024 18:43

boland: They are depreciating very quickly.

Don't worry about depreciation. New vehicles have always deprecated quite quickly but it's not like you're selling anytime soon. Work out the savings over the time of ownership (including maintenance which is nearly nil on EV's) along with having a new vehicle. The V2L capability is fantastic and I wish my Tesla had that (or Tesla's had it in general). For longevity the BYD's are the better buy due to the BYD blade batteries that are lasting really well.

I did just see the Powerwall 3 is available in NZ: https://www.tesla.com/en_nz/powerwall (only just got that email) so not sure if you're quoting the Powerwall 2 or 3 in your pricing. Not sure of the pricing of the 3, but could be worth having another look there.

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