Fifteen years ago, one of the hardest parts of selling solar was explaining why your panels shut down in a blackout. No grid meant no power, even on a sunny day.
Today, batteries fix that. Yet I am seeing thousands of homes getting large batteries with either no backup at all or poorly designed backup. That’s because – as batteries go mainstream – a set of myths has taken hold.
Let’s knock them over.
Myth #1: You should not even bother installing backup
Some shonky retailers actively advise against any backup, blaming warranties or vague electrical issues. This is rubbish. Good hardware, installed properly, can back up a home or essential circuits, and it is covered by warranty when done right.
Of course not paying for backup can be a valid choice if you live in an area where grid outages are so rare to not worry about, but any retailer advising all their customers against backup without consideration of their local grid’s reliability is showing their cards: they don’t have faith in their subcontracted installers to handle the slightest complication. Avoid these retailers at all costs.
Myth #2: Backup must be whole house or nothing
The opposite of the retailer who is scared of wiring a backup circuit is the retailer who claims anything less than a whole-house backup is subpar. Whole-house backup is not always the best choice. In many homes, backing up only essential circuits is smarter. Your battery lasts longer, avoids overload, and delivers power where it matters when you can’t top up from the grid.
Myth #3: Backup limits self-consumption
I am now seeing at least one new-to-Australia manufacturer claim that if a circuit is not backed up, it cannot use the battery for self-consumption. That is horseshit from a clueless support team. A battery can both support normal daily use on all circuits and also provide backup on only essential circuits. These two things work together with proper design and well-trained installers.
Myth #4: Three-phase homes need three-phase backup
If you are putting a battery on a three-phase house, it’s a valid design to use a single-phase battery system. I only back up one phase on my three-phase house, and it works perfectly, including solar charging the battery during blackouts1. Don’t be pressured into spending more on a three-phase battery system if you don’t need or want it.
The good news is that these backup myths are excellent filters. For sure, any retailer who repeats Myth #1 or manufacturer who repeats Myth #3 should be filtered out immediately. If they cannot get backup right, they are not the people you want designing or supplying the most valuable electrical system in your home.
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
- You only need a three-phase backup if your existing solar inverter is three-phase and you want to AC-couple it, because the solar needs to see all phases to keep running. ↩
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Our initial installer, whose work mostly had to be removed and reinstalled including some wiring, tried to tell me the only time the battery could supply the house was if this big contactor in the system disconnected the grid! So only circuits on back up could be powered by the battery. (Insert expletive of choice here) hilarious.
Minor point re your start to the blog; there are a few inverters that will supply power when the sun is up giving battery free back up during the day. Some Fronius models, will not sure of others.
That the grid must be isolate d from the circuits that are backed up is true. Fronius’ backup uses 2 contactors do this when wired according to Fronius’ instructions.
Yes, but you need to be careful, the problem with backing up only 1 phase of three phase is you need to put all your essential circuits on the 1 phase, which means you will probably need a bigger inverter than otherwise.
They still flog a lot of 3 phase solar systems with inverters only capable of 5kw per phase, 5kw is pretty useless for more than minimal backup functionality.
“They still flog a lot of 3 phase solar systems with inverters only capable of 5kw per phase, 5kw is pretty useless for more than minimal backup functionality.”
Huh? 5kW/phase/15kW total gives the same capacity as a standard 63A single phase grid connection that most households have. As long as the circuits are spread fairly evenly across the 3 phases, whole house backup is easy with the only caveat being large DOL motors. Those are increasingly rare these days with inverter A/C’s and pool pumps being standard issue.
I’ve had 2 x 8 hour planned outages on a 15kW 3 phase inverter and nothing changed for us – A/C ran, EV charged, dinner was cooked in the electric oven etc…
Obviously your backup must be of all three phases… not just one.
Sorry, I didn’t realise you were talking about installers only backing up one phase of the three. That would indeed be sub-optimal (and lazy).
A trap that cheap pricing may bring is backup on 5kw inverters.
Sure, that might work for small homes, perhaps a retired couple or even a working couple.
Backing up the most essential needs is important, doing the whole shebang and you might get wasteful . . . even with basic needs, circuits with LED lighting through the home, fridge(s) / freezer(s), kitchen sockets, computer power, and maybe even a split (or 2 ?) in sleeping areas, it can be a lot of draw.
That’s going to be a problem if these things are needed simultaneously, minor draw items, say 2 splits, the fridge cuts in, someone wants a coffee = brownout or juggle things.
I reckon 10kw inverters should be a minimum in most homes that want a decent back up, and of course then the battery size and the solar to keep it topped off realistically for perhaps up to a few days (or a week ?) means the inital investment is quite high . . . a lot of solar sales people want cheap so it makes an easy, fast, dirty sale.
Myth 1. If you don’t get blackouts where you live, or they are so rare they don’t bother you then why pay $1,000 to $2,000 on wiring backup and changeover switches or installing Gateways plus the cost of upgrading all backed up circuits to Type A RCDs? It’s not retailer laziness, it’s intelligent spending. Putting that unnecessary spend on backup into another battery module makes more sense.
I believe Solar quotes are based in Adelaide. Perhaps your grid is less stable than other places like Perth
Hi Drew,
If you really look into reliability… as more renewables are deployed the grid reliability only goes up. SA was the most reliable grid last I checked. It’s so obvious even the Liberal party was claiming credit for it.
https://reneweconomy.com.au/five-years-after-blackout-south-australia-now-only-state-with-no-supply-shortfalls/
However that didn’t stop a few storms creating isolated week long blackouts here and there.
https://www.electranet.com.au/strength-reliability-boost-to-south-australias-electricity-network/
I’m also in Perth. Unplanned blackouts are very infrequent and generally fairly shot so I don’t believe they should be the #1 selling point for spending extra money on back-up capability. I already have enough off-grid power to get by (a small 12V system I’ve had for years with a 200W inverter to run computer, TV, modem etc. and now the MG4 V2L if I can’t live without doing the ironing or making a toasted sandwich).
Still, when the time came to install my Sungrow battery we included back-up capability. Seemed silly not to.
I agree, in 10 years I’ve had less than 1 hour of unscheduled outages. I have the switch gear at home to do the isolation, haven’t installed it yet because it’s not urgent.
Backup is optional. If outages are rare where you live and you are happy to ride them out, skipping it can make sense.
What I am criticising is retailers pushing “no backup” as the default for everyone, without asking how often the power goes out or what matters when it does.
Finn, its good to point that detail out, I think most posters just respond without reading a few letters or responces first. I am surprised at the almost lies some installers mention and its a pity householders do not know how to get a second opinion.
I have whole house backup on 5kW. It’s never been a problem as; if you’re home you just turn off non-essential loads and if you’re not home there won’t be any non-essential loads. Our Backup only kicks in after 3 seconds so any air cons shut themselves off and don’t restart when the battery power kicks in. Otherwise I guess it would be possible that we be away from home and have left the oven and all the air cons running when the power goes off. But that would be a pretty rare event. I’d say our washing machine and dryer also wouldn’t automatically turn back on after three seconds of disconnect either.
I have noted recently that quite a few appliances remember their operational state when a blackout occurs. My dishwasher does this, as does my TV.
The TV doesn’t draw much current and it’s not likely to be on when no one is at home, so it doesn’t matter, but the dishwasher can be consuming quite a bit of power as it heats its own water. So if a blackout occurs when the dishwasher is on, it could result in an uneccesary discharge for the battery.
Not sure if my dishwasher would kick back in. I haven’t had it running when the power went out. The three second delay is a SolarEdge “feature” and other Backup systems are instantaneous with no loss of connectivity.
Solar / battery should be about future proofing, and not only for ever increasing power pricing.
Les- perhaps I’m misunderstanding your argument, but you seem to make the case for going the full shebang, or else there may be situations where you are caught short (e.g. two A/Cs, fridge and kettle), therefore you recommend a 10kW inverter minimum. But then you make the point that it gets quite expensive.
Isn’t that just the point of sizing the back-up appropriately and not necessarily going for full-house backup? In that case, a 5kW is probably ample for many households. Indeed, in our 3 bdr house with 2-3 occupants, including one WFH, in 6mths of solar, we have only consumed more than 5kW on two brief occasions (a few minutes each time), and that’s with no prioritising or scheduling of usage. So we could essentially do full-house backup on our 5kW inverter if we had to. (currently no battery, so it is a mute point, but it is likely a future addition).
Backup was the one reason we went for a battery! Our installer wasn’t overly bright. We have a SUNGROW battery, where backup is standard, and luckily we read Finn’s pages. As he described his SUNGROW backup system and how it worked, I went outside to check ours, but it wasn’t wired up! A quick phone call and days later another installer completed the job. Thanks, Finn!
The backup works very fast; even our computer doesn’t go off. We only know because our air purifier in the bedroom goes off when we get a blackout.
I think we survived 4-5 blackouts. One of our best decisions, even without the rebate.
Please excuse my apparent ignorance, but I assume your backup system provides power to your whole house during a blackout as if the mains was still available, and there is an isolator that drops the connection to the grid for anti-islanding.
If so, why does the air purifier go down?
I was thinking the same
I had a stand up argument with the installers of my first Tesla battery. They were adamant that they could only back up a small part of the house but could give no sensible reasons. Took a couple of long phone calls back to their office “experts” before they pulled their head in.
I have enough panels that as long as the sun is shining I can run everything forever including aircon and cooking. Sure, the more I run, the less backup hours I have after sunset but that is my problem not the supplier’s.
I had the same problem. Had to push and push to get whole house. Got it eventually.
I have 3 x Powerwall 2’s and 2 solar systems (8kW and 10kW inverters) on 3 phase power.
In a blackout only phase 1 of my home is backed up – lights, fridges/freezers, TV, Internet and a few power points. It has proven very very handy in about 10 days of blackout in 4 years.
When I bought the second solar system and second battery in a package the installer told me before installation that both solar systems would recharge the batteries in the event of a blackout.
Come installation day the installer had difficulty setting that up and spoke to Tesla on the phone. He said that Tesla said only 1 solar system could backup the batteries in the event of a blackout. That is how it is setup.
I would be very interested to know if that is also BS…..
Hi John,
I have 2 powerwall 2s and two separate solar systems. One 5kw and another 6.67 kW each has it’s own inverter. The solar systems and the powerwalls were installed separately, as in the original 5iw system in 2009, powerwall 2 in 2019. Then 6.67kw system in 2020 and second powerwall 2 in 2023.
I can confirm that three powerwall “sees” both solar systems as 1 single entity and has no issues with them working with both powerwalls.
I’d say BS indeed
Regarding #2,
It’s a shortcut. It is A LOT easier to backup the entire house than selected circuits.
Doing a partial backup takes more time, usually requires adding a separate enclosure (which quite often won’t fit in the meter panel), rewiring (and sometimes extending) all the backup circuits to the new enclosure… And customers are wondering why it costs so much to do backup.
A full backup is easy. You place your inverter between your mains and your switchboard and you are done. No re-wiring.
Yes, that’s definitely the case with Victron battery inverters – wire the grid to line in, and loads to line out. No effort, no fuss, just an installer configuration setting. It’ll even apportion battery and grid supply as needed to supply load, short of a complete failover, if desired.
All it takes for it all to be simple, is for someone to know what they’re doing.
We are still in a pioneering phase, complete with an uneducated consumer base. That some installers are equally uninformed reinforces the wisdom of my brother’s path – engage a system designer to map out a system to meet your written requirements – and include in the contract, a commissioning test. In his case that included throwing the grid isolator, on load, to see if the lights flicker or the computer borks. (Oh, OK, that does require the consumer to think through *all* needs … and not all manage to anticipate all of them. But with 25 kWh of batteries, installed 5 years ago, full backup is no issue for him.)
I have a 15kW 3 phase inverter and my whole house is backed up across the 3 phases using two simple 4 pole contactors, each with 2 sets of NO & NC contacts.
Works a treat, A/C, oven, EV charger, all power and light circuits, HWS are all backed up. Of course you have to be sensible – charging the EV at 11kW while baking a cake and heating water is out, but life is pretty much unchanged when the power goes out these days (6 outages last year, 2 of them > 24 hours.
Hi Beau,
Sounds like a good setup you have there. I take it you have a series connected inverter with the whole house switched to the backup port when the mains fail?
I’d be curious to know how the contactor arrangement is set up.
I assume they’re energised by the mains, so an outage means they spring open. The backup port is connected to the NC contacts with A & B phases through one and C phase through the other contactor?
Hi Anthony
Yes, spot on with everything you said. I have 1x Chint NCH-8/11 (1NO, 1NC) and 1X Hager ESC465 (2NO, 2NC). A Phase connected to the Chint, B&C phases connected to the Hager. Grid supply wired to NO, EPS port wired to NC. Loads wired to other side of NO and looped to neighboring NC. Coil energised by the grid.
Grid drops out, coil de-energises, loads now isolated from grid supply and connected to EPS port. I have to use this arrangement because FoxESS H3 inverters cannot (for now) be set to energise the EPS port upon loss of grid, its either permanently on or off. Single phase KH & H1 inverters can be set to energise EPS only upon loss of grid so you can reverse the above connections and energise the coil from the EPS port, preserving the contactor coil.
I’m not sure that Myth #1 is a Myth for everyone. I had less that an 1 hour of unscheduled blackouts and 2×8 of scheduled outages in 10 years.
I actually have the switch gear at home to support blackouts, but haven’t bothered to install it. I’ll do it at some point but it’s not urgent.
Backup is optional. If outages are rare where you live and you are happy to ride them out, skipping it can make sense.
What I am criticising in Myth #1 is retailers pushing “no backup” as the default for everyone, without asking how often the power goes out or what matters when it does.
Yeah it may be optional and some people might have limited outages.
But when you have outages (planned or not) and 2 young kids at home and $1000 of food in the fridge/freezer its great to have Internet, TV, lights and power for the fridge/freezer as a minimum.
The longer the outage the more it’s worth. One of our outages was 72 hours (regional NSW).
Hi John,
It’s a little difficult to put a price on the labour involved too.
Cleaning out a freezer, separating all the plastic & disposing/composting all the contents is a chore.
In some instances the dog will eat like a king I suppose…
Please dont give your dog things not safe for you or your kids to eat. I’m a vet & well – it’s expensive for some gastroenteritis & especially treating panreatitis. Not fun for the dog either.
At the tail end of Covid, the grid was down in our street in Tecoma for 5 weeks – in winter. I was slow to react, and on the second day it was impossible to buy a generator in Melbourne. It took a while before some were trucked in from NSW. I managed to make coffee and some hot food on a camp stove perched on the electric stove, but soon escaped to off-grid heaven in Gippsland. (After a week, a hot shower is no longer just a luxury.)
The game has changed. Piddly 5 kW inverters went with piddly 6.6 kW arrays in the old days. Amateur hour has been displaced by lower cost higher capacity equipment, fit for purpose, on a thin grid, or off it. 100% backup is simple and effective. A big array and battery, plus a generator input on a substantial inverter, make for a capable system. Build or buy a house on high ground, and prepare adequately over the next two decades. It will be worth the effort.
That’s fair enough Finn. There are certainly people where unscheduled outages are so frequent the price of a backup solution would probably more than cover the cost of spoiled food over the life of the system.
We got panels in 2024 and batteries last year. I kept stressing that backup capability was one of the most important things for us (being a pessimist and expecting more blackouts in the future). Cost was not really a concern, functionality was. I was surprised by the difficulty I encountered in getting straight answers, particularly re being able to recharge during a blackout. I still don’t know whether that is possible. I think we ended up with a standard single circuit backup option – but to be honest I don’t really know how to turn it on. It was weird – people were raving on about how quickly the backup would click on (differences in terms of seconds), but I believe there isa switch in our meter box that I have to flick over? So what’s the point.
Hi Peter,
What exactly did you buy in terms of make and model?
Hi Anthony, we got an AlphaEss Inverter (Smile G3 – B5) 5kW, and 2 x Smile G3-BAT-10,1P
Hi Peter,
I just had the AlphaESS inverter and 2 x Smile13.3P batteries installed. I am of the understanding that the failover to backup is automatic and virtually instantaneous. You should double check that the installer wired the backup circuit(s) correctly.
Myth 4 –
AS/NZS 4777.1:2024 – phase balance – 3 phase
Where single-phase inverters are installed for both ESS and PV they shall be installed on the same phase.
Maximum rated apparent power imbalance of all IES shall not exceed 5 kVA between phases.
Putting aside the option of multiple single phase units on each phase since that is not what is being discussed for the “myth”.
Unless you are going to install a 5kW storage system only single phase solutions on 3 phase are very limited if you apply the standards, that have very good reasons for existing to prevent neutral issues.
I just had new panels and batteries installed. During design phase I was adamant that I wanted whole house backup and was assured that was no problem…. It was a big problem!!
Installer said that my setup could only handle 21 Amps and that even if they backed up the whole house the inspector wouldn’t pass it. To do it, they said, would require a different battery setup in order to cover 64 Amps to back the whole house up.
Unfortunately, that was just one example in this whole installation that was WRONGLY designed and advised by my chosen company.
So, now I only have a couple of essential circuits backed up and will not even be able to run a single aircon unit during a blackout. I installed nearly 27kwhs of batteries – though they are limited by a 5kw inverter.
I had panels installed a few years ago, and added a second battery and backup recently. I noticed that just after the recent install that at night (no solar generation) but with fullish batteries, sometimes there was power going from the batteries into the grid, and sometimes power from the grid into the house. This would change backwards and forwards several times a minute. It wasn’t large amounts, but seemed unfortunate that I was selling power on the cheap one minute, then shortly after buying it back at a much higher price from the grid even though the batteries were almost full.
I rationalised it away as being some sort of ‘balancing’ requirement, but is that unavoidable?
I haven’t checked recently to see if that was still happening.
Lost power for 6 hours a week or so ago.
It was 43 degrees outside and with full house backup in catastrophic fire conditions I and the mob that joined us were more than happy that we went the whole way on backup.
We went through a 7 day blackout during the Black Summer fires, but have had very few since and those were short. Nevertheless, I’m concerned about the blackouts of the future, also due to increasing storm activity (we’re south coast NSW).
We would like to include air con in the backup, so are tempted to go with the full/gateway solution we’ve been offered with a SIG battery system with 10kW inverter.
We’ve heard that, re the back up tech, SIG offers a similar level of functionality to Tesla (?), including storm watch mode and manual charging from grid in anticipation of bad conditions (?).
Any comments/feedback gratefully received.
Thank you (am new to the battery game, learning on the go…)
Sigenegy has a decent backup solution. The only thing to be wary off is the size of your AC for start up surge if it’s an old unit it can be a significant peak surge higher than running current. You won’t have an issue on-grid but depending on size might be a problem off grid.
I don’t recommend 10kW if you’re talking about 3 phase either, 3.4kW per phase far to small for many people.
Yes it has a storm watch, as reliable as weather data…
However you can manually set whatever reserve power in battery you want to keep.
I recently survived a multiple day outage with out issue with a Sigenegy. But I do have a lot of solar and thus kept the battery charged each day from own generation.
Thanks very much Darren,
We asked re black start capability (is that what you were referring to?) and the advice was we’d need to set the app to “off grid” before the battery drains completely to support that. Does that address the concern you raised?
We are single phase. The proposal is to add 8.8kw to an existing 10yo 4.9 kw system (max we can get due to shading), plus 16kwh battery with 10kw SIG inverter. We’d like to be able to run (low) air con on backup, assuming weather permits sufficient output/charging while off grid, and are considering an EV in the next 5 years.
This combo prob isn’t optimal, but we’re struggling to justify the numbers of going to a larger battery (unless we get the EV, plus not sure we’re the right types for the Amber/VPP option to boost the ROI). So we’re thinking to maximise the panels on the roof for now, and maybe expand the battery later.
Point taken re weather forecasting!
Thanks again.
Oops sorry Darren just re-read your message (obviously half asleep the first time) – you were talking about the air con. So, basically, we are on single phase and the 10kW inverter is intended to support the intended system/use (potentially including daytime EV charging) and maybe system expansion.