Last week, I mentioned a bloke who was beaming after placing his order for a new 30 kWh home battery. The plan was simple: charge it with solar during the day, then use it to both run his house and charge his EV at night. He reckoned he was set for energy independence.
Here’s the problem: unless his installer has done some careful system design – and unless this budget battery actually has the control interface required – he’ll still be pulling power from the grid every time he plugs in his car.
What the Fine Print Reveals
The retailer’s marketing looked impressive, but the small print told a different story. Backup power during a blackout? That’ll cost extra.
That’s already a red flag. Most people assume a home battery always provides backup. It doesn’t. Always check the quote and get it in writing.
Then I dug into the datasheet. It was billed as a:
“30 kWh battery with 5 kWh hybrid inverter.”
There’s no such thing. They meant 5 kW, not kWh. If the people selling you the system can’t tell the difference between power and energy, that’s a worry.
Why 5 kW Isn’t Enough
A 5 kW inverter1 running a 30 kWh battery is like trying to drain your hot tub through a drinking straw.
To fully charge from solar in winter, it would need about six hours of perfect sun. To discharge, the limit is still 5 kW.
Now think about the EV. A standard single-phase home charger pulls 7 kW. That means as soon as the car plugs in, the battery can only cover 5 kW of that demand. The missing 2 kW? Straight from the grid.
Add in the rest of the household loads – cooking, lighting, heating, hot water – and the grid is doing even more work. The battery will run out of power way before it runs out of energy.
Can It Be Fixed?
In theory, yes. A good installer can set up a smart EV charger to monitor grid draw and throttle the charging speed so you always stay under the 5 kW battery limit. But that requires:
1. A battery, inverter and EV charger that support those smarts.
2. An installer who’s sat down with you and worked out your load profile.
I’ll be blunt: at under $10k for 30 kWh installed, I doubt either of those things have happened.
The Bigger Picture
The federal battery rebate has triggered a flood of deals on oversized battery systems.
Cheap, giant batteries are flooding the market. And they’re being sold like flat-pack furniture: one size fits all, just whack it in the garage and “energy independence” is yours.
But batteries aren’t flat-packs. They’re high-energy machines that only pay off optimally when the design matches the household. Without that, the dream of “no bills” becomes a reality of “mystery imports.”
So by all means, grab a 30 or 50 kWh battery while the rebate makes them tempting.
Just don’t expect a cheap, cookie-cutter install to make your bills disappear. Without proper design, all you’ve really bought is an oversized box that still needs the grid every night.
Phase Shift is a weekly opinion column by SolarQuotes founder Finn Peacock. Subscribe to SolarQuotes’ free newsletter to get it emailed to your inbox each week along with our other home electrification coverage.
Footnotes
- Even 10kW hybrid inverters often allow 10 kW of solar power but only 5 kW of battery power – always check the specs! ↩
About Finn Peacock
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Honestly, should 5kw inverters even still be a thing? It would be a small household indeed that never used more than 5kw of power at once during busy periods these days.
People selling systems with a 5kw inverter are no better than snake oils salesman in my opinion.
Secondly, charging an EV and a big battery from your solar array is still a big ask if you are draining them both significantly daily – given the size restrictions on both inverters and arrays imposed by regulation. That means a very well designed system is required.
Unfortunately the biggest inverter you can connect to the grid in WA is 5kw.
Hi Durra,
That’s not entirely true these days. Fronius has set about educating the authorities so they’ll allow 10kW per phase now.
Anthony, does WA understand programmed export limits, I wonder? In NSW there’s no problem having 20 kW of inverters on a 10 kW export limit. All that takes is a CT on the grid connection, and a very small amount of smarts. It’s old tech now, thoroughly proven in extensive on-grid use.
I don’t know if Victoria is equally with it, being off-grid here, with the BEV as the only export opportunity.
The only substantive effect of limiting self-generation to the export limit is to unnecessarily deprive households of more than minimal self-consumption, I submit. And given a low export limit, that perversely boosts national CO₂ emissions, to global detriment.
oh wow, that’s ridiculous.
With a 5kW inverter, an all electric home can cover most of its loads, most of the time. People with Powewall 2s know this. Drawing a bit from the grid briefly when you put the heating, induction stove and oven on might cost you what, 50c? It’s not like you do this everyday. And if you’re smart, you can avoid it.
Regarding the EV example, why do you need a 7kW inverter if you’re going to charge it from a battery (ouch efficiency nerds like me) overnight? You’ve got tons of time.
I’m not saying that 10kW isn’t better. It is. But unless you want to export to wholesale or you’re on a demand charge, the annual savings of having a 10kW over a 5kW inverter will be what $20 per year. Even if it’s $300, you probably saved more money by getting a cheaper system
Agree David I find the same. I have 40kWh battery and it’s filling plenty for my solid use, from solar and a couple of wet days from Amber at 9 cents kWh. Most days still above 20% in the morning so can fill it up from my 13.2kWh solar even with 5kWh inverter. If I need to use my ducted RC power is always available and only exceeds 5kWh briefly. Stopped using gas for heating now too. I am hooked up to 3 phase house with single phase inverter [3 phase smart meter] and also working well with brief power outage this week my fridge and a few circuits working from battery. I am in credit with Amber with best day credit $4 but not fussed about pushing extra back to them.
To the ev charger using. 7 kw. thats only the case if the person has a fixed not movable charger in place that charges the car similar fast than the type 2 charger from the charging station. Otherwise it might be just a regular charger that uses between 8 pr 10 amps that just plugs into any powerpoint even a 3kw generator that I always take with me just in case and have used plenty of times on my Nissan leaf EV. Those regular chargers that come with the cars look like a very big laptop charger and take ca dopple the time to charge than those 7 kw chargers. And in an YouTube movie I’ve even seen someone charging a Tesla on a 2.1 kw generator.
Sorry if this has already been mentioned ex but 1st July 5kW limit was raised to 10kW in WA.
Very true Andrew,
I just had a new system fitted and because my preferred Option of a 8kw Inverter with multiple batteries 30kw, would not fit sideways along my internal garage space available and rules that apply
So the only option the installer gave me was a smaller 25kw vertical stacked, but with only a 5kw Inverter sadly 😥
That means you can only ever draw 5kw at an instant ever from my batteries 🔋
Which is easily exceeded if you switch your HWS to heat up and a moderate air conditioner load during the evening.
So say goodbye to any dreams of being VPP
Take care
Andrew, I’ll second your motion. It’s grid-mandated misdirection which has some outdated thinking stuck in the Tiny Inverter Trap. There’s proven to be no big battery or inverter limit, I find.
My on-grid brother’s solar set-up with 25 kWh of LTO batteries was installed 5 years ago, and there is zero issue, because it was designed for purpose. He has 8 kW of battery inverters + 12 kW of PV inverters, and a 10 kW export limit. There is ZERO relation between that limit and inverter size(s) – just export throttling instead.
My off-grid system’s inverters, with 46 kWh of LFP batteries, are pumping out only 10 kW at the moment, into the BEV, HWS, two aircons, and two fridges – 14 kW earlier today. With 24 kW of inverters, that’s a modest load. The DC coupled arrays are supplying 8 kW, the AC coupled delivering 3 kW, with capacity to spare.
Energy resilience requires load-proportionate generating capacity. How hard is that to understand, really? Half measures half do it.
5kW is a fantastic and useful size. Most things solar ramp in 5kW (h) rates. 5kW is a manageable installation in many terms- the wiring is manageable at approx 20A- many installs will make fo with 4mm wiring, 6mm gives a decent overhead. 15kW inverter is a much more complex install.
The big issue is units that don’t allow any expansion/parallelability. The CEC should really address this as it creates huge waste and lost financial efficiency. This is where Victron is amazing. I’ve only set them up off grid- but I’m sure CEC listing isnt far away if not already there. I have a system with 15kW solar and 38kWh battery running a machinery shed- utilising 3kVa inverters-10 of them. Started with 3x3kVA, slowly upped to the now 30kVA total. I have set up plenty, most with parallel units. I have installed few standalone 10kVA and 15kVA systems, but they can easy expand too.
Moral of the story is the hardware we install really should be modular, upgradeable and COMPATIBLE.
John, when I last looked, there were half a dozen Victrron inverter models on the approved list. As my brother has had two Multiplus 5000 inverters on-grid for 5 years now, any approval paperwork delay is at least half a decade behind us.
Anthony must be busy, or he’d remind that Selectronic is a solid Aussie alternative, but I too have found the Lego-like Victron building blocks, including MPPTs and system controllers modular and easily expandable.
But even AC coupling half the system, with a pair of Fronius inverters was easy expansion, using delta-f throttling for management by the Victrons. (It can also be done via comms, if the Fronius has Victron-compatible firmware installed.)
You have laudable system redundancy – there’s only 2 battery & 2 PV inverters here, for minimum off-grid redundancy. With 12 kW of Fronius & 16 kVA of Victron, compressor starts & welding are no issue, even on battery alone.
I have a hybrid inverter and 10kwh storage im running 2400w single string of panels. My daily use over 10kwh but as i use high drain appliances during peak solar my storage is almost full by sundown. If needed i run a 3.5kw generetor for an hour in the evening. Using 1.25 l of fuel. Completely off grid. Solar has produced 13.5kw a day a couple of times and i get the manufacture stated max 400w per panel on these days. I assembled my own battery and solar instal. Hybrid smart inverters are easy to set up if you read their manual. Obviously full cloud cover days require generator to keep batteries topped up. Im still paying far less for power than i was on grid.
Simon, are you tempted to whack up another string or two of panels, now cheaper than ever, and stop paying for petrol? Most inverters have two string inputs, anyway.
well the reason they exist is default grid limits.
many areas have a default limit of 5kw per phase.
can you have more? yes but it’s on a by application basis. you have to apply for it.
this was done as a way to reduce grid upgrades and to try and reduce curtailment.
you can get export limiting inverters too but they are more expensive.
Another great piece, I’m seeing so much of this in the community now, bigger is better status games. To link it back to another recent post from you about efficiency, we have a single Powerwall 2 at home, have had it about 3 years. When the rebate happened, I thought hmmm, do I need a second Powerwall 2? And then I zoomed out and looked ay my design not of the hardware, as you talk about here, but the design of my weekly energy use.
And I realised for example that our EV travels a few hundred kms per week, mostly on Thursdays and Fridays. And that it can do that without recharging, so that if I leave that until the weekend it can all be from our own solar. Previously I was charging overnight, every night, using cheaper overnight rates. But I realised I didn’t even need those, through consideration of the design of our own energy use, another dimension of design that should probably precede any solar install? Maximising self-use, as you say, but that needs design.
yes how you use power matters. and that is the bit people forget about.
you can make quite a difference just by changing how and when you use power.
energy efficiency and efficient use is the side of the coin that is often forgotten.
Chris, the sun spills into the infinite black abyss, as much surplus energy in a second as the world uses in 650,000 years. There is no efficiency benefit once solar meets all needs, and that’s more a capacity consideration than efficiency, given enough batteries and generation diversity to defeat clouds and night. Just kill coal and ICE transport now – that is absolutely essential.
For those with limited roof space, solar & wind farms increasingly provide low cost energy, free at midday. With zero fuel and operating emissions costs, we already have intermittent curtailment, because of excess free energy.
We are now spending over $1T p.a. to boost generation exponentially, and x3 to x5 excess capacity will go in for uninterrupted supply.
Energy abundance is galloping at us, and it has nothing to do with AI.
Material – the opposite, until population falls, as it will.
Thanks Finn. As usual, critical information for those of us who are seek a good quality, well designed and supported installation under the current rebate system. I have learnt so much here that, while at times overwhelming for my small, non-electron focussed brain can be a bit too much, but at least I now know the main traps to avoid and the right questions to ask.
I have recently requested you provide me quotes for expanding my system with addition solar and a battery and I will probably buy an EV with a larger capacity battery in the not too distant future. But my charging will be predominantly at home. Blackout coverage will be useful but not critical as the infrastructure locally is relatively new and seems reliable. It will probably outlast me!
I know what I need and want I now know what I don’t need and don’t want. Extremely useful. Some of my friends who have bought big systems at very reasonable prices may not necessarily have received what they hoped for.
Patrick, especially if retired, BEV range + judicious use can greatly boost self-consumption. I’ve delayed BEV charging through the last six consecutive dim overcast days here, running it down a bit with trips to town – to finally charge today in a little 3hr, 20 kWh, catch-up. Even without V2H, that effectively extends the house battery a bit, as it similarly performs consumption time-shifting.
Solar-surplus-only would have charged it over the 6 days, but I find it convenient to just whack in 7.2 kW when it’s sunny. That predicates a sufficient inverter or two – best to have with a BEV or other substantial loads, to avoid grid draw.
A grid isolator and islanding capability is easy, if manual switchover is sufficient for your needs. Automatic failover can be pretty simple too, given adequate inverter capacity.
Thanks Eric I am retired, I will be living in a well insulated house (when I finally finish it!) with a rented flat powered from the same system (so no control on usage there) in the temperate climate of the mid-north coast of NSW. I will be able to manage/time shift loads as necessary.
But I want minimal hassle or maintenance and time input to all this and I am not the sort of person who will constantly watch an app or spend time changing parameters. I don’t want to spend time monitoring and setting it up, I have much more important things to do, including travel! After a long career sorting out complex problems in government and business and having to learn heaps of new systems and processes I am over it. My objectives are ease of use and little or no bills.
So getting it set up properly in the first place by the installer is important to me. I am about to have a discussion with the people recommended by Solar Quotes and hope they know their stuff and set it up properly.
5kW is indeed too low for, let’s say, running a ducted AC system. For the EV, if the charger is a DC charger, and directly integrated without having to convert from DC in battery to AC and then back to DC, it could work.
I have ordered a SigEnergy stack which has a 40kWh battery, 10kW inverter and a 25kW DC charger. This goes with a 15kW solar panel array. I also have OVO Energy’s EV plan which allows for cheap charging between 12am and 6am, so it should work well.
I only have 5kW, and run AC splits throughout the whole house totally fine, never had an issue. As well as charge an EV overnight.
yeah it will work fine. but how much did you draw from the grid?
it may be hard for you to tell depending on what inverter you have or other power monitoring.
like Finn says your inverter is rated for 5 kW if your load was 7kw the extra 2 was from the grid and you paid your full tarrif price for it.
Ashley, I can see yours moving from its current exemplary status, showing the imminent future to all, to a common standard in 5 years max. Its utility and fitness for purpose must quickly become generally evident.
Some say AI ought to foster abundance, despite that fact that is produces nothing, but it is overflowing solar energy which is beginning to do that where sufficient panels and batteries are installed – whether privately or gridscale comes to the same – it’s all equally CO₂-free beneficence.
Ashley, I might be wrong but I believe the Sig inverter needs to be of similar size to the EVDC charger. Pls check before you buy…
No, that it is the good thing about the DC charger, it doesn’t need to be converted to AC from the panels or batteries. The inverter size only comes into play if the PV + battery (the batteries can provide 20kW) is unable to provide the full 25kW.
‘But batteries aren’t flat-packs. They’re high-energy machines that only pay off when the design matches the household. Without that, the dream of “no bills” becomes a reality of “mystery imports.”’
I think “no bills” is a myth unless you go off grid. As more batteries come on stream, DNSPs will have to increasingly recover more costs from the fixed daily usage charge than from energy supplied. I’d predict the daily supply/service charge will eventually be a fixed cost greater than the kWh charge. Which is fair(er) to those who have batteries, but not so much to those can’t afford them. My 2 cents worth.
And regarding battery inputs and outputs, something of a surprise to me was that the new Powerwall 3 has max 8kW in (although if it doesn’t have at least one expansion pack it’s stuck at 5 kW) and 11 kW out. As much as I hate Elon, I have to admire Tesla tech.
For me (with a 32kWh battery and 10kW inverter), the big problem with a 5kW inverter would be with exporting excess to the grid within the window of time in which it is profitable. With a 10kWh battery, you wouldn’t care so much because you’d be self-consuming mostly. But there is no point to 30kWh on a normal home if you aren’t going onto a wholesale tariff (Amber) and using some of that capacity to earn some shortening of the payback.
I am finding a 90 minute peak window in which I average 15kWh of exports for a couple of bucks on a daily basis works great (added to which some serious price spikes will get me about $1,000 a year).
Given that taxpayers paid for nearly half of it I also think powering three other homes through dinner in the peak on renewables without involving the transmission network matters as well. a 5kW inverter couldn’t do that job and therefore the rebate shouldn’t allow one on a bigger battery.
I’ve gained a good general understanding of the Australian battery market from this article, but as a non-technical person, I need practical, accessible advice on adding battery storage to my existing solar setup (10.4 kW panels, 8.5 kW GoodWe inverter). An installer quoted me an AC-coupled system: a 5 kW Hiconics inverter and a 30 kWh battery. I’m also planning to purchase an EV early next year and install a heat pump water heater. Is the proposed setup suitable for significantly lowering my electricity bill and maximizing self-consumption across my solar, battery, EV, and hot water needs? I would greatly appreciate guidance or suggestions for optimizing this system design.
I’d consider a larger inverter. Your AC coupled solar, if maxed out at 8.5kw, then only up to 5kw of this can be charging the battery. That means unless you have at least 3.5kw of constant load in the house, you will be exporting some of your solar, not maximising self consumption. It also compromises your ability to charge quickly from the grid during free/cheap power periods, in cloudy conditions. An 8kw inverter would probably be a better match for your existing system, or larger if you plan to add more panels in the near future. The capacity of the battery, 30kwh, should be more than enough for a typical household.
I have 40kWh battery with 5 kW inverter. 13.2Kw solar. Running my ducted RC in Winter and pool pump/bore in Summer – rarely exceed 5kW [on startup] and not at all fussed as saved up front the price difference of going to 10kW inverter. Feeding back with Amber enough power to keep my usage in the positive. No EV.
Keeping the purchase price down kept my battery ROI to under 3 years after Fed and State VPP rebates. [SA $2k]
Plus using more power now [AC] and saving $ not using gas for heating.
Daughter with 20kWh battery and 5 kW inverter also very happy {split AC}
I got 2x11kWh BYD batteries installed to pair with 6kW fronius inverter, so it would all work well with fronius ecosystem and wattpilot too. Except no one told me that BYD HVM battery modules 11kWh stacks can only charge or discharge at 4.5kW. And to fix this I need to add more modules to the stacks to raise the voltage. And I used the subsidy for this first install…
Ah, yes, the Little Battery Trap: Each battery type has a maximum (dis)charge
rate – for LFP, that can often be between 0.3 and 0.5C if you want maximum cycle life. Your 4.5 kW limit on an 11 kWh battery is pretty typical, then. That seems ample in your case, though, as 2 x 4.5 = 9 kW, which is more than your 6 kW inverter can deliver.
But given a bigger inverter, or two of them with ample PV, it can be worthwhile to install a bigger battery, well above daily consumption, to grab solar yield during limited clear skies, not least here in Spring. If off-grid, it’s advisable – else the generator gets a workout.
The experience makes you more expert now, so you can be the one able to tell others. 😉
yeah, I thought that too when choosing an option with 2 stacks of batteries, but as it turns out they will charge as slow as 1 stack. From what I understood the limit comes from the fronius 22A limit on DC connection to batteries. HVM modules are 51v nominal each and I have 4 of them in a 11kWh stack, so ends up 204v * 22a = 4.5kW
If I went for a smaller capacity 19kWh but one stack with 7 modules the voltage would be higher and the max it can accept would be around 7kW, so the inverter would be limiting at 6.2kW.
Damn, no wonder you’re miffed. That’s a Tiny Inverter Trap on today’s standard battery capacities, slightly ameliorated by the high voltage, but not enough to write home about.
If it were me, the battery sizes are similar enough that the extra opportunistic yield from 6.2 kW charging 19 kWh would outperform 4.5 kW & 22 kWh in most variable weather, I sense. (Not that there’s heaps in it, admittedly.)
I’m just back from a 65 km trip in the MG4, bringing home 8 bags of cement in the back. At 100 km/h, that’s used 23% of range; the sun’s still shining, and I’d rather recharge with 6.2 kW PV + 1 kW battery to whack in 7.2 kW, leaving more for overnight than 4.5 kW PV + 2.7 kW battery draw. (I just figure that production trumps storage once a workable amount of storage is there – a good day’s worth bare minimum. There is admittedly a fuzzy use-case-optimisable balance in the middle of panels/inverter/battery relative sizing, so long as there’s enough of each.)
Referring to “Even 10kW hybrid inverters often allow 10 kW of solar power but only 5 kW of battery power – always check the specs!”, what do I look for in the specs? Is it Max. Charging Power?
I’m getting the Goodwe GW9900-ET-20 and the data sheet notes Max. Charging Power is 15kW. Not sure what that means because the inverter is 10kW.
My install will also include Goodwe Lynx 28.8kwh battery, Goodwe smart meter GM3000 and a changeover switch. Is the smart meter good enough to manage the system? I have 10kw solar panels (no more room on roof for more, sadly!!).
To further confuse me, the installers won’t remove the original inverter (Goodwe 10kW) and will AC Couple the new hybrid inverter to it. Do you have any articles on managing multiple inverters?
Cheryl, others will be more familiar with Goodwe products than I, but even then, a little bit of clarification might help. We read that both the old and new inverter are 10 kW, and you have 10 kW of panels. If the inverters are to be AC coupled, does that mean that the changeover switch is on the DC side, allowing solar array switchover to the old inverter if the new one fails? (There would presumably then be neither battery charging nor utilisation, until repaired.) Some instructions on a big fat equipment label would then be helpful even to an expert coming in cold. The installers should provide adequate documentation – before you pay them.
In general, there is no reason why a hybrid inverter with 10 kW AC output can’t deliver 15 kW on the battery charging port. That would be a nifty design, allowing faster storage of excess sun for later use. Only a bigger battery like yours safely allows that! But full utilisation of that would need more panels. Add a carport, perchance? 🙂
You’re a gem, Erik! I am so grateful you took the time to reply and I’m in awe that you responded to at least 20 comments!! 🤩
Same as Tommo, I have tried to get panels onto my pergola roof but I’ve been told it’s not able to safely hold the weight and I’m asked “is it worth it for extra 4kW?” (Yes, was my answer and I got eye rolls)
After bugging the installers, I have this information now:
Panels connected to old inverter which converts panel DC to AC for home usage and export to grid (I don’t have any limits because it’s an older install) and now, it also sends solar power to the new hybrid inverter to charge the batteries.
Changeover switch is for the new hybrid inverter in case of failure in the hybrid inverter or the batteries then when I flick this switch, it will basically cut off the new set-up and return to drawing power from grid (or solar).
Cheryl,
While the Yellowbox pergola I built 40 yrs ago still stands, I’d not put panels on it now. A galvanised steel pergola would last – but the cost is painful. A new wooden one with sufficient 10 x 10 cm hardwood posts, and ample roof members, roofed in zincalume to exclude weathering, could readily be made to take panels. My porch does.
I agree entirely, another 4 kW adds up very healthily over a year – it would more than cover my aircon loads, given the 46 kWh battery to carry over sun gaps. Add a BEV in the next decade, and too much is just enough, I promise.
OK, I understand the changeover is Grid/Inverter, i.e. going off-grid (islanding) in the event of a blackout. With enough battery capacity (kWh) and hybrid inverter power (kW), you could power the whole house as long as the battery lasts. My brother does that with 19 kW solar, 25 kWh battery – with an electric stove, multiple fridges, freezers, and aircons. With exports, they pay him every year. Only 5% imports.
Your Goodwe proposal sounds a bit like mine. I only have 4.8kW panels from 2018 but I can see I could get around 10kW if I replaced and expanded it in the future but it’s functioning well for now. I too considered a carport expansion but after asking around, got a few blank stares when I mentioned this and what strength requirements the carport would need. I’m surprised it isn’t more common.
have you read this story – these look to be a great idea.
https://www.solarquotes.com.au/blog/vela-solar-carport-mb3237/
Downsides to retrofitting (that I know of), which I hope Anthony will do an in-depth article on, are:
– Batteries won’t charge from solar if grid is not connected. I’m told it’s because the old inverter (connected to the panels) is grid tied (that’s all I have, I don’t understand what grid tied is or why it can’t force charge the batteries)
– Backup will work in a black out but you’ll essentially be draining your batteries without any incoming charge
– The rest of the house that isn’t backed up won’t have electricity during an outage even if solar is in full generation.
This is not ideal for me but the only way around this is to get new panels, new wiring to go straight to the hybrid inverter. That’s gonna cost a lot and I just invested in this battery so not gonna be something I can do for a few years.
Cheryl,
They appear to be telling you that the old inverter isn’t directly parallelled with the new, so it would also go off-grid via the changeover switch. That’s nuts!
It normally slaves off the grid, stopping if that fails. On changeover, the new hybrid inverter must grid-form if you are to operate off-grid at all. Then it substitutes for the grid, allowing the old inverter to still contribute while there’s sun.
The hybrid inverter should charge batteries whether on of off-grid – unless they’ve cut corners in the design, so it can’t supply load and charge simultaneously. That’s crappy consumer-hostile incompetent design, not fit for purpose in the 21st century. (Admittedly, my brother and I both have separate PV and battery inverters, for full system flexibility, charging *whenever there’s sun*, no excuses!
Whole house on batteries, overnight & in blackouts, is only a matter of sufficient battery and inverter sizes. Mine does it every night, brother too.
(Errr, and budget. Oops)
I currently have a 8.8 kw PV system coupled with a 8.2 kw fronius inverter and 2 x Tesla powerwall 2. No EV !
Seems adequate for my low energy use household.
As more people intergrate batteries with their PV systems, requiring less electricity from the grid and surplus electriciy being supplied to the grid during the day.
The electricity retailers lower the feed in tarrifs to near zero and increase the un avoidable daily supply charge.
My minor issue is with my Solar Hot water (collector pannel type with 3.6 kw boost)
Connected to controlled load 1.
I want to remove the CL 1 as I am paying a seperate daily supply charge.
I want to boost my hot water via my own solar suppled electricity.
What is the best way ???
I am on the North coast NSW.
Hi Brad,
You already have a Fronius, it already has a relay output to control a load so you’re half way there.
Get a contactor installed to activate the HWS when it’s sunny.
https://www.solarquotes.com.au/blog/using-fronius-inverter-smart-meter-relay-make-solar-electric-hot-water/
Controlled loads are usually on a (DNSP) dedicated and separately metered circuits and as such are not fed by your solar system.
In SE Qld I had to contact my electricity retailer to remove CL1 to pool pump. There was a cost to me to have it removed (metering charge) but may not for you. You would need to talk to your retailer about removal and if any charges will apply.
Beware as your retailer may move you to a different electricity plan as your current one may not be applicable once CL metering is removed.
It’s much more satisfying and cost effective knowing you’re using your own clean generated power.
Another option is to get one of the Catch units. I have the Catch Green that diverts solar to the hot water when available. It can also top up at night from the controlled load if necessary (I can set it to top up for 2.5 or 5 hours). Or I can heat at any time from peak power.
It’s not cheap (added about $900 to my solar install), but it’s been very good. I’m happy to keep the controlled load connection as a back up. The connection fee for me is only $3.80 a month.
Can someone tell my why the daily supply charge is unavoidable? Our system has been operating for 13 months now, and we only drained the battery on two occasions this July. Typically, we are still above 30% each morning, and even the most overcast days still generate enough solar juice to keep us going. So I’m tempted to close our retailer account, since the FIT is now next to nothing, and not bother engaging with an alternative retailer (with a lower daily supply charge) until next winter. But no one else seems to be doing so. What have I missed?
Oh, and what are my chances of getting the retailer to cough up the unused Federal power rebate?!
I have had a few suggestions, not sure which way to go as yet.
My main wish is to
1 : be rid of the additional Controlled Load 1 daily charge.
Have my thermal solar hot water system
(Rinnai 315 ltr, 3.6 kw boost)
This system rarely needs boosting during the summer months, only winter and inclement weather.
2: boosted using my own produced electricity, either directly from Solar PV system or batteries (2 x Powerwall 2)
or a mix of both.
Thought on a fox ess 9.9kw single phase inverter and 29kw battery set-up my current system is 9.6kw solar
The components seem proportionately dimensioned, if the inverter’s charge rate is similar to its AC output. That would be about as much as you can whack into an LFP battery of that size, if you want long cycle life.
It looks fine for domestic use on-grid. If off-grid, more solar panels would help avoid running the generator after a couple of dim days, but 29 kWh battery could suffice even there, for some households.
Then if you have a BEV on the horizon, the inverter could deliver 7.2 kW for full whack BEV charging, but need a drop from 3.6 kW to 2.4 kW on the HWS element in order to do both without taking anything from the grid. The PV array wouldn’t deliver all of that, though, so a moment’s thought on how far off the BEV is, could pay off. (Yes, the BEV can be charged slower, or the excess can be grid-supplied. Depends on the game plan, really.)
Hi Erik,
You seem across system designs.
I’ve had 14.4kwh Enphase (with microinverters) for a few years. Recently got a 40kwh Sigenstor Battery with 15kwh inverter (three phase). Car charger goes at a max of 11kwh.
Does the design seem about right?
I’m yet to get my handover docs from installer so hope there’s no issue with the retailer or DNSP re size.
Dan, you’re going to find out now, aren’t you? 😉
OK, it’s hard without a provided knowledge base – but there are system design courses run in NSW & Victoria, if infrequently. Even a 1-day one is great for a householder with enough caffeine on board to benefit a lot.
But your system sounds very workable. The 15 kW 3Ø inverter can run a lot of house/workshop loads, given some throttling of the EV charger from it’s nifty max rate, when house loads are over 4 kW. If the EV charger has solar-surplus-only smarts, that’s automatic and hassle-free.
The 40 kWh battery is x3 on what your PV might yield – that’s an optimal ratio with LFP batteries, I’d contend. And 40 kWh would amply serve many folk even for off-grid. Your ambitions, given 3Ø, might aim higher, but you have grid reserve, so worry-free.
As you’re on-grid, 14.4 kW PV seems good. More aids self-generation in poor weather, but a big battery substitutes.
You’re only 5 kW/Ø generation – even a backward state can’t complain.
Thanks for such a thoughtful and helpful response Erik.
I started with a standard 5kw setup with Goodwe grid tied inverter and 2 arrays. I use around 8kw per day. The set up I now have is a Victron multiplus 2 5000w inverter in tandem with the Goodwe and is not grid tied. I have 19500w AGM Batteries ( 200ah 48v). In NQ the tariff between 11am and 4pm is 7 cents. The Victron uses the solar power ( apprx 30kw per day)first and then uses the grid ( a rainy day)to recharge the batteries and the HWS in the 7cents period. All excess is sent to the grid at 8.3cents. Generally the solar is sufficient to do the recharging and I rarely use the grid. I am well aware that the AGMs do not have the same lifespan as lithium but as a rule I rarely go below 70% discharge which will guarantee a reasonable life. I can switch one array through to the batteries side stepping the grid system completely if there is a blackout.
If there is a blackout and I am economical I have three days of power without using solar.
I will continue in new post
Carrying from previous post. Now the costs at current prices. Victron multiplus 2 5000w $1100. 8x 200ah AGM Batteries $2640. Not including labour ( for me $1000 which i will not include) . Therefore for a total of approx $3800 I have a setup which will probably last for 5 to 6 years which I can replace the batteries or I would assume there will be better and cheaper batteries ie. sodium or whatever available then. For those starting afresh without solar but with an open inverter and batteries being charged 7cents a kw makes it very attractive with the ability to grow without being locked into a proprietary system.
Lachlan, sodium batteries exhibit much greater discharge voltage droop than LFP, e.g. on a nominal 48v battery: 60-40v
But a Victron Multiplus handles 38-66 Vdc, so it’s sodium compatible, I figure.
SoC will just plummet toward the end, as ever more current is drawn to maintain power output.
I hear your “open system” and scalability message – not least since adding a substantial PV array need be no more complicated than banging in another MPPT. And if that’s ELV, then it’s DIY to boot.
I went for two Multiplus 8000, as three Multiplus 5000 wouldn’t fit between the windows in the workshop wall. It’s like Lego, with a gratifying choice of building blocks – entirely avoiding the upgrading pain caused by inflexible consumer style single purpose offerings.
QLD Energex has a somewhat hard 10kw inverter limit as well, even when the export allowable is only 5kw (or lower).
For those who have existing solar installs around the 5kw mark, adding an AC coupled battery is hard without replacing the existing perfectly fine inverter. You can go 5pv +5 battery, but can’t do 5kw pv +10kw battery without a custom connection agreement – even if that battery inverter capacity is purely for self consumption.
Bruce, is it that Qld doesn’t yet understand programmed export limits, or is it just that the equipment in question lacks the simple facility of export limiting? I remember a number of blogs in past years, talking of a CT or smartmeter on the grid connection, so that much is old hat.
In NSW, 20 kW of inverters on a 10 kW export limit is no issue, and hasn’t been for at least 5 years. Maybe Qld can catch up with the tech one day.
Admittedly, depriving prosumers of reasonable self-generation capacity does improve corporate profit, at the expense of climate mitigation.
What about dc coupled systems?
Dean, mine is 50% DC coupled, with 10 kW of MPPT charging capacity, with 13 kW of PV feeding them. So, yes, you’re right, that’s immune to the Tiny Inverter Trap.
But a substantial battery can only deliver whole-house oomph through an ample battery or hybrid inverter/charger, and mine offer another 11 kW of charging capacity, fed by a pair of Fronius PV inverters off another 14 kW of PV.
So that’s 22 kW of charging capacity with just 50% DC coupling. (5 kW limit? Pffft!) My brother has 20 kW charging on-grid, 50% DC coupled, also, no tiny inverter trap there, either.
Within budget, the biggest battery trap is going too small, as that can limit (dis)charge rate below useful levels, even if you’ve installed an adequately sized inverter – 10 kW minimum, I figure.
If in a dopey state without soft export limits (yet), I’d take half the system off-grid, with a battery inverter driving off-grid loads, so its output can’t be counted in prosumer-hostile bureaucratic nonsense.
Thoughts on 28.8kWh battery with 7.5kW inverter? 6.6kW existing solar panels.
Upgrade to 10kW inverter is additional $1350.
No plan to buy EV car, but planning to add heat pump to replace gas in the future.
Hi – I have an AlphaESS SMILE-G3-S5 system installed with 10.1KWH battery and 7.04KW of panels. Have had it since February so have seen both summer and winter conditions. I work in electronic engineering so have an understanding of the technicalities, although I not an expert in domestic solar equipment.
Overnight careful management is needed for the battery to go the distance, with grid use up to several KWH per night. Daytime exports are usually over 10KWH, even on moderately bad days.
First question – if I doubled my battery capacity, would that be potentially worthwhile? – I could avoid the careful management and would avoid excessive export.
Second question – The system is specified as having 10KW max solar input. How is this used? Does this mean it can battery charge at 5KW, while also supporting 5KW load? Or does only process 5KW total, regardless of solar total?
Further comment – I can always stay within 5KW total consumption, without trying too hard.