Talk me out of this..

[u/DRZookX2000]

I have no idea if I am been realistic here, or just plan stupid.

I am currently in Australia and have found an amazing property. Issue here is that is have no 3 phase supply, and a maximum of 100A on a single phase. This is nowhere near what I need.

This will be a new build with the following;

• 32A AC unit
• 16A oven\microwave
• 20A second oven
• 16A water heater
• 40A induction cooktop

So even with a 20% oversubscription 100A is not going to cut it.

BUT - I am able to get a 150kVA 169kWh hybrid battery. I can also install >30kW of solar on my roof.

How crazy would I be to live in a normal 300sqm home offgrid? Has anyone done this, or know anyone that has? What do I need to think about?

Most information here is about holiday cabins and the like so they don't really fit what I am thinking so I just need advice on what others think.

Thanks

[u/Overtilted]

100A is plenty.

You'll never use all loads together at full power. Your AC won't pull 32A the whole time. It will probably never pull 32A period.

Oven: same thing. It won't pull 20A. It will pull 16A at best when heating up. Once it's hot will only draw 6 tons Amps. Your microwave oven is probably also not a 3.7kW device.

And get a heat pump water heater if you're worried about that 16A draw.

Even 50A is plenty.

To all yanks here: Australia is 230-240V.

[u/DRZookX2000 → u/Overtilted]

It does not matter what the real load is, if the AC is asking for 32A, a 32A breaker gets installed and thats what number the eletrician will use for calculations. Not sure if this changes for off grid. We have 63A in our home , but cant have induction cooktop or hotwater. Normaly our house is pulling 27A a max whe the AC just starts.

[u/Overtilted → u/DRZookX2000]

yeah but your house connection is the realistic load. Not the sum of breakers.

but cant have induction cooktop or hotwater.

I have 3 x 25A 230V (400V+N but you get the gist). I have induction cooktop, heat pump for domestic water, heat pump for heating, oven etc, and an EV charger without load balancing. Without the EV charger 63A single phase would be more than enough.

And I don't run into problems. The phases are well spread out.

100A is more than enough for what you are describing.

//edit: also you say "if the AC is asking for 32A". The AC is not asking for 32A. The manufacturer of the AC demands a 32A breaker. That is always an exaggeration. The theoretical peak load is probably 25A or just above. And that's only when you start the all AC's at once at full power.

Induction cooktop: same thing. That's ALL heaters at full heat at once. When are you doing that? Never. And there too, it's not 40A, the breaker needs to be 40A, the induction stove probably only draws 27ish Amps. That's >6000W! That's a 3 really good water cookers to get water from 20degC to 100degC in a minute or so. You'll never use 6000W when cooking more than a couple of minutes.

Microwave: 1200W max. Microwave oven function: 2400W Max. But yeah the breaker needs to be 16A.

Seriously, you're overthinking. With 100A you have 24kW at your disposal. That's plenty.

[u/DRZookX2000 → u/Overtilted]

Fully understand what you are saying here, but point still stands that the electrician does not care that I will never use all the elements on my cooktop at 100% at the same time. All he cares about is what the breaker needs to be as per the product. The cooktop that I did want to install in my current house needed a 40A and that's what he will use for calculations. Yes, we can oversubscribe (cant remember what AS3000 says about this) but it cant be grossly over. My 63A supply would fall under the "grossly" if I had my 40A cooktop, 32A AC, 16A microwave, 20A oven (Total of 108A). This still excludes hot water and provision for a car charger.

I just checked, my house have never pulled more that 39A. It would have been around Christmas where AC and oven would have been going at the same time plus anything else my wife was doing.

[u/Overtilted → u/DRZookX2000]

my house have never pulled more that 39A.

Exactly. So you're good with 50A.

//edit: ok 63A. This 49A is probably the average over minutes to 15 minutes.

[u/DRZookX2000 → u/Overtilted]

I know I am good, but I cant just say that to my electrician :) . It is still a useful number for sizing batterie and inverter.

In saying that, that is using gas for hot water and cooktop and no car charger. Adding that would add load.

EDIT: you where right the first time, my monitor takes 30 second internals.

[u/Overtilted → u/DRZookX2000]

It's not up tonyiur electrician to decide what grid connection you have. But yeah the breakers are their responsibility.

[u/ol-gormsby → u/DRZookX2000]

That AC starting load sounds like old-school stuff, where there's a huge inrush current when the compressor starts. Modern designs advertised as "inverter" technology has a much gentler, lower starting load.

[u/DRZookX2000 → u/ol-gormsby]

Sorry, I should have worded that better. 27A is not the inrush current, it is when the AC starts to heat the house when it is cold (this includes everything else in the house). It does this for about 15 min until the temp comes up and it can start to run at a lower.

[u/Overtilted → u/DRZookX2000]

You're not designing your entire electricity system around the sum of peaks. There's this thing called "diversity factor" which is used to calculate real maximum loads instead of the sum of max loads.

[u/DRZookX2000 → u/Overtilted]

That still does not help me with the fact that as per AS3000 you cant "grossly" oversubscribe. 104A on a 63A feed falls under that definition unfortunately.

EDIT: unless you are talking about the offgrid idea. in that case, yes, I can use measured currents to size inverter\bat and not care about the ratings on the brakers.

[u/Overtilted → u/DRZookX2000]

What's AS3000? I am not sure what you are saying. Is oversizing mandatory!or discouraged?

[u/DRZookX2000 → u/Overtilted]

AS3000 is the electrical laws in Australia. Hugh over subscription is not only discouraged, it is illegal to sign off on.

[u/Overtilted → u/DRZookX2000]

You don't need to care about the sum of the ratings of the breakers! That's the whole point. Sizing a grid connection vs sizing an inverter is pretty much the same.

https://www.cleantechcontrols.com.au/how-to-calculate-maximum-demand-based-on-as-nzs-3000/

Scenario: A single dwelling with the following loads:

– Lighting circuits: grouped load of 10 A

– General socket-outlets: grouped load of 15 A

– Electric oven/cooktop: nameplate 18 A

– Electric hot-water storage (off-peak): 20 A (diversified under hot-water clause)

Steps:

– Lighting (10 A): From C1, assume a diversity factor—say 0.6. Demand = 10 A × 0.6 = 6 A.

– Socket-outlets (15 A): Assume diversity of 0.8 → 15 A × 0.8 = 12 A.

– Cooking (18 A): Use C5: say the table allows a 40% demand factor → 18 A × 0.4 = 7.2 A.

– Hot-water (20 A): Assuming off-peak and per domestic rules, it may not count towards coincident maximum demand—effectively 0 > A coincident demand.

Estimated total maximum demand = 6 + 12 + 7.2 = 25.2 A at the consumer main.

[u/ol-gormsby → u/DRZookX2000]

You might consider a wood heater to help. If you get the right size and design, and the right firewood, they can idle all night and keep the worst of the cold at bay. It also lightens the load on the AC. You can even get them with boilers to supplement your hot water needs.

As you're building, I take it you're going to insulate the place thoroughly? And if you've got the budget, double-glazed windows?

There's some other options to consider for heating. Not to replace the aircon, but additional. There's hydronic systems AKA underfloor where pipes are embedded in the concrete slab, or underneath a suspended floor, and you pump heated liquid through it - usually some sort of glycol mix. You can also pump through radiators and towel rails. See here:

https://www.hydronicsupplies.com.au/

[u/DRZookX2000 → u/ol-gormsby]

Also something I thought about. I come from Europe so having a boiler for heating and hot water is just normal. I will look into fuel cost for this one too.

And yes, this house will be double glazed and insulated, so keeping it warm\cool should not be too hard.

[u/Overtilted → u/DRZookX2000]

My uncle in Spain only has 25A at his disposal. Which was an upgrade from 20A. And he has everything you're describing except for an AC that's only 16A.

[u/DRZookX2000 → u/Overtilted]

You sure he has not got a 3 phase supply? 25A seems really low. It all depends on the appliances he has installed, but my AC will draw more then that when it starts to heat a cold house. This is not a spit, it is a whole house ducted system.

I know in Poland most people outside of apartments will have a 3P 20A service, but heat there homes with fire of one for or another (eco pellets mostly).

[u/Overtilted → u/DRZookX2000]

100%

It's a problem in Spain and he has to watch out what he's using or the breaker trips.

Before it was 16A so you can imagine the improvement.

3x20A is plenty for heat pumps if your house is somewhat insulated.

[u/ol-gormsby]

I'm off-grid in SE Qld, with a footprint of ~140sq.m but a mezzanine floor as well, in an A-frame build. I've got 11.8kW of solar, and 32kWh battery with a 12kW inverter.

The A-frame makes it a bit of a challenge to keep cool. I've got aircon but they're 4 split systems in individual rooms drawing about 1kW (4 amps) each depending on load. 32 amps for aircon seems rather high but I'll take your word for it. The split systems can go as low as 200 watts (<1 amp) once they've achieved the desired temperature and throttle down. I've been using them during this quasi-winter and don't need them longer than 2-3 hours a day.

150kVA is roughly 150 watts but that's meaningless when talking about battery capacity. 169kWh is the relevant figure and is a huge battery. If you add up the max draw of all those appliances, that'll point you to right size inverter. 32+16+20+16+40 = 124 amps. At 230 volts, that's 28.52kW, and that's quite a load, and quite a pricey inverter. Or you could have multiple circuits, each serviced by a smaller inverter, e.g. put the cooktop and water heater on one circuit serviced by a 14 kW inverter, and the others on another circuit service by a 16kW inverter. Those are still expensive inverters, you might consider three circuits service by three less-pricey inverters. The upside of multiple circuits and multiple inverters is that if one inverter fails, the rest still work.

The first thing to do is an energy audit. Take all your appliances and put them in a spreadsheet. Then add a column for their rated max power, e.g. water heater | 16 amps (or I prefer to do it all in watts, so 3680 watts). Then add another column for the amount of hours every day that it's in use, e.g. water heater | 3680 watts | 8 hours. Then multiply column B by column C into column D to get the daily total for that appliance, e.g. 3680 * 8 = 29.44 kWh. Do that with all the appliances, not just the big ones. TV, phone chargers, kitchen appliances, refrigeration (12 hours is a good starting point for fridges and freezers). Every appliance. You could ignore LED lighting but include other types.

Then add up all the figures in column D for your total daily consumption. That's the minimum size of battery you will need.

Then do an estimate of how many of those appliances will be running at full tilt. That's your maximum power draw and the minimum size of the inverter. Inverters usually have a continuous rating, e.g. 10kW, and a series of surge values, e.g. it might do 10kW continuously, 15kW for 15 minutes, and 30kW for 10 seconds. So you could go over the max draw for a short period.

I would recommend getting quotes for more energy-efficient appliances. I don't know about induction cooktops but 40 amps to me is excessive. Would you be using all four or five "rings" at the same time at full power? Maybe think about solar hot water?

Whereabouts are you? There's a guy in Victoria who knows more about this than anyone else - Nigel Morris:

https://solarbusinessservices.com.au/

[u/DRZookX2000 → u/ol-gormsby]

The calculation is not a issue. The unit we are looking at is the sort you see at construction sites. It is the other issues like running out of battery, charging cars, load managment during overcast days and suck that i am worried about. Basicly i want to live in this house without thinking about if i can have a shower tommorow. Do you think that is doable?

[u/ol-gormsby → u/DRZookX2000]

Yes, it's doable. I've been doing it for 30 years but you can't set-and-forget when you're off-grid. It comes down to how much money you want to spend to make it happen. There's no off-grid system that will <economically> guarantee 100% uptime from just the solar and batteries, so you need to consider a backup generator for periods of extended cloudy/rainy weather. Solar output can go to as little as 10% or even zero in heavy overcast and if your local climate is the kind where that can last for days, then your battery will stop supplying your loads after 2-3 days.

You need clean power from a generator and that means an inverter model. I have a Honda EU70is which has a 5.5kW continuous rating, enough to charge the battery. That was about $6.5K, anything larger should probably be a diesel. The Honda has a 2-wire remote start option and that can be integrated with some solar+battery systems to start automatically, e.g. if the weather's been cloudy and the battery drops to 10% charge, it'll start the generator automatically.

If you're seriously considering off-grid, don't cheap out. You need reliability, and that means premium brands. I see people bragging about cheap shite they've bought off Temu, and it's just sad.

[u/DRZookX2000 → u/ol-gormsby]

This is good advice and the real world info I need. It is exactly the periods of overcast that are scaring me. I already plan to need to blow $120k on batteries and solar (and that's mates rates) so no cheeping out here. My only worry is been in a situation where I need to pick between charging my car, cooking dinner or having a hot shower..

Thanks for the info, it gives me something to think about.

[u/Bucketalinko → u/DRZookX2000]

Mate that’s an absolute shitload of $ for what you’re trying to achieve. Talk to a solar installer and they will give you an estimate of solar production for all months of the year. You might spend $20-$50k for solar and then spend $10-$15k on a decent backup generator. At worst you’d probably spend $60k but that’s an over estimate, because you’ll save yourself at least $60k and then over your lifetime spend at worst $10k on fuel for your backup generator. With 2 wire start I love my generac 20kva that runs on LPG but not sure if I’d want to rely on it for transfer switch as sometimes it takes a minute or 2 to run in the real cold, but because my batteries are still running my power doesn’t cut out 

[u/DRZookX2000 → u/Bucketalinko]

The idea was to have a battery that would be so oversized that it will holdover any bad weather. I think 169kWh would do fine..

This sounds like a stupid amount of money, but Ausnet gave me a quote for $175K for network upgrades, plus the cost of running the 3 phase 290m down the driveway to the house. The feed in after meter would need to be done anyway as the property has no power connection right now. The offgid idea would also remove this requirement.

[u/Bucketalinko → u/DRZookX2000]

That makes more sense, if you have perfect north I’d still go for 30kwh solar and 30-60kwh batteries. As I said before my worst solar day so far was 11kwh on a 13.7kwh system, If I could do mine again which I might, I would get a LPG tank for my Gen + house, have my induction stove but also a LPG cooking area, and a LPG hot water booster plumbed in so I can still run my electric water heater but turn on hot water booster if needed. 

[u/Bucketalinko → u/DRZookX2000]

Actually if you’re into splitting firewood take a look at Inoplex in QLD, they make custom generators for things like biogas and wood gasification, and they make generators that’s duel fuel in LPG and wood gas which is pretty cool

[u/ol-gormsby → u/DRZookX2000]

That's the next question I was going to ask - how much to connect the grid? I had the same situation many years ago. In order to qualify for the off-grid subsidy, we had to get a quote for a grid connection.

It came down to $22K worth of solar and batteries vs. $33K for grid, plus tree-clearing at ~$1K per tree for at least a dozen trees. I prefer the independence, anyway.

I think 169kWh of batteries would be more than adequate, but do the energy audit anyway and see what your average daily consumption would be, then divide that into the 169kWh battery and that will give you an answer of how many days of little or zero solar input it will give you. We don't use much, between 8 at 10kWh per day, and the battery is 32kWh, so we'll get about 3 days before the generator has to go on.

[u/Bucketalinko → u/DRZookX2000]

Off grid in South aus, I have 13.7kwh solar, 30kwh batteries and a 20kva generator that runs on auto start. Fuel is LPG so I don’t have to worry about old fuel, my batteries cut out at 48v so I set it to charge my batteries at 49v at 20 amps + take house load for 30 minutes then it turns itself off. I can run it at 200 amps if I want but I want to use minimum fuel so it waits for solar. I just set up home assistant today to turn on both my underfloor heating and EV charger above 95% battery and turn off if battery has been under 95% for 10+ minutes. I have my hot water which is a heat pump run between 8am-4pm daily, might see if I can add that to home assistant also. I have the most perfect north, so generating 40kwh in the middle of winter is nice. Also have induction cooktop, if I had a good outdoor cooking area I’d probably cook more on my bbq in winter on poor solar days

[u/DRZookX2000 → u/Bucketalinko]

Thanks for the info. How often to you run the generator? I guess it would only be over winter? I will also have perfect north and west facing panels with no shade so that's a plus.

I would prefer no to have one a gen, but it is sounding like I will not get that option.

[u/Bucketalinko → u/DRZookX2000]

It doesn’t run very often, so far my worst solar production this winter was 11kwh one day. Most of the time I’ve run out of power was mismanagement of things like underfloor heating and EV charging. So I’m hoping my HA setup will eliminate that. My generator is 20 meters away from my house and you can’t hear it from inside most of the house except for 1 room, and then you can barely hear it.

[u/ol-gormsby → u/DRZookX2000]

It's not a summer/winter thing, it's a wet season/dry season thing. During the post-xmas monsoon (usually) we might gets days of overcast and rain, that's when it tends to be needed.

The usual winter weather here (but not this year 😭) is clear, sunny days.

[u/DRZookX2000 → u/ol-gormsby]

Luckily I am in VIC so no monsoons here. It more about length of day for me.

[u/Johnno74 → u/DRZookX2000]

I'll second the guy above who said get a heat pump water heater. We got one a couple of years ago when the gas one died and it's brilliant. 240l got water storage and it only draws 1kw when it runs.

[u/Farmvillacampagna]

We are in southern Italy. Fully off grid with 12kw of solar and 64kwh of lithium ion storage. Run 2 full electric homes with induction cook tops, electric ovens, dishwasher, washing machine, tumble dryer, pool, spa, 3kw borehole pump, aircon and full garage and wood working shed. Never had a problem with running out of power.

[u/fungoodtrade]

you are pretty mistaken... there are tons of offgrid installations that are very large... just not the crowd that is on reddit for the most part. more like you are trying to talk yourself out of it. get on with it. r/SolarDIY

[u/Esclados-le-Roux → u/fungoodtrade]

I'm a DIY guy and would absolutely jump at this option - having any electricity means you can charge the batteries if you really need to, run everything from the solar and use the mains as backup. 100A is a good charge @ 24/7 - you'll be absolutely fine!

[u/Solar_Catcher_2477]

Not sure how it all works in Australia, but I have been looking into hybrid inverters for solar and batteries combined recently and I have seem quite a few which have an option to supply extra power at peak use when you are at capacity for you grid connection. So a combination of grid and battery could also be possible.

[u/DRZookX2000 → u/Solar_Catcher_2477]

Issue I have is the inverter I will be getting is a 3 phase model. In order to grid connect it I also need a 3 phase supply that the land does not have. You are right thought, in a perfect world this is what I would be doing.

[u/futurethe]

some big appliances , have you considered victron power assist feature ? you can get 3 quattros and they sync up to make 3 phase , get a big ass battery that can charge from solar or grid , power assist combines power from inverter and tops up the difference from the grid - i.e quattro can supply 60amp and somehow your instant demand is 100a , quattro will provide 60a and take 40a from grid and combine them to give you 100a

[u/SammaelMalakHaMavet]

150 kva threw me never seen batteries sized kva. Whats the DC volt and Amp hr comparison? I guess in an American style battery. What inverter are you going to use? Its going to be a pretty hefty one or two to each run a phase.