Lately at SolarQuotes, we’re getting slammed with this question:
“I’m gonna get a battery at some point. Should I get a hybrid inverter or a regular grid-tie inverter?”
That’s the million-dollar question. I know which one I would get, but I’m not you!
First, let’s get this out of the way: A ‘battery-ready’ solar PV system is just a marketing term for a PV system with a hybrid inverter and no battery. Although designed to integrate batteries into your grid-tied PV solar system, hybrid inverters aren’t the only option for adding batteries later.
Any solar system can have batteries added later. Whether it includes a hybrid, string, micro, or stand-alone (off-grid) inverter, you can retrofit batteries to the whole lot. But which one is right for you?
Hybrid inverter plus DC-coupled battery on the left. String inverter plus AC-coupled battery on the right. These two look very similar, but they’re not the same!
What Would I Get?
I’ll cut to the chase. My personal opinion is that relying on promises of future tech to dictate your solar PV system choice now should go in the bin along with so-called ‘expandable solar systems.’ If you’re not ready to add batteries right now, it may not eventuate, so don’t let it influence your inverter decision.
That doesn’t mean you shouldn’t add batteries later!
If I were hypothetically forced to decide one or the other, I would err on the side of a standard grid-tie string inverter. Although I’m not a betting man, this choice gives me better odds of fulfilling my future battery plans. If I were buying a PV system from scratch with a battery, I would choose a hybrid inverter. But that’s just me!
Why? Let’s Break It Down
String inverter systems use AC-coupled batteries, and these batteries are ‘inverter agnostic’. That means they’re connected to the AC side of the electrical system, and it doesn’t matter a hoot which brand, or how many1 inverters are also connected.
On the other hand, hybrid inverters are DC-coupled and have compatibility limitations. Only a select number of battery models will work with each inverter. Not only that, but there’s no guarantee that your chosen battery will be around in the future, so when it’s time to install it, you might get caught with your pants down.
Although there are other factors to consider when picking an inverter, this one alone is enough to sway my hypothetical decision in favour of a string inverter when hoping to add a battery later. It’s like an insurance policy to strengthen my chances of fulfilling my plans.
Will your chosen battery be around when it’s time to drop your money? Place your bets now at Kim’s Casino! (my odds are crap.)
More Reasons To Play Safe
- String inverters are simpler devices, so installing one without batteries is a lower upfront cost compared to a hybrid inverter. Notice I said ‘upfront’ cost? That’s only part of the cost if you want the installer to return and do more work.
- Technology changes quickly! By choosing an inverter-agnostic AC-coupled system when it’s time to add a battery, you’re more likely to be able to take advantage of future technology and less likely to be locked into a particular brand ecosystem that may not support a chosen product later on.
Or Risk It For The Biscuit!
Maybe I’m playing it too safe? Boring! Hybrid inverters with batteries offer several advantages over string inverters AC coupled with batteries. Why not take a punt? You gotta risk it for the biscuit, right? In defence of the ‘battery ready’ hybrid inverters:
- Hybrid inverters are specifically designed to work with battery storage systems and are more efficient. They will marginally convert more solar power into usable electricity. Also, monitoring of solar generation, battery storage, and energy consumption is usually integrated together and viewable on a single app. Nice and tidy!
- Retrofitting a battery to a hybrid inverter is easier than AC coupling one to a string inverter system. That’s why they call it ‘battery-ready’. In the long run, it may2 be cheaper to choose a hybrid inverter over a string inverter, considering the initial solar install and then having the installer return to add a battery.
- You can put more solar panels on your roof (if you have room) with a DC-coupled solar battery system because the 133% oversizing rule doesn’t apply. Bear in mind that the installers aren’t allowed to connect the extra panels until you have the battery installed. This comes back to my initial point of making a bet that the necessary products will be there when you need them.
Line diagrams – Left: AC coupled string inverter system. Right: DC coupled hybrid inverter system.
Why Not Stick In A Battery Right Now?
I have no doubt that people are asking this question in the first place, mostly because they’re waiting for battery prices to come down. I can’t help you there, sorry, but I’ve laid out a pretty good case for both inverters. Now it’s time to make a case for installing a battery right now rather than later (BTW, I’m not for or against home batteries, and definitely not trying to sell you one!)
- All my misgivings mentioned above.
- If you’re thinking about a battery, no matter what inverter you choose, installing it at the same time as your solar is cheaper. You’ll save a ton of money by not having the team return a second time. I would say it goes without saying, but I’ve said it.
- They say a week’s a long time in politics, and the same rings true in the solar industry. Is your installer going to be around after all your procrastinating? Are the network rules going to be the same? Electricians typically aren’t keen on taking on other installers’ previous jobs. Their hands are tied to current regulations, which can lead to headaches and extra costs passed on to you.
A Couple More Things
Although a hybrid inverter is meant to be DC coupled with a battery, you can still add an AC-coupled battery to your system. All the stuff about being locked into a particular brand may not materialise. It’s not ideal though, and a waste of money if you pay for inverter features that you’re not using.
Lastly, don’t forget to tell your installer about your future battery plans during the design stage. Take that into consideration with regard to inverter location, possible battery location, switchboard modifications, and future cabling for battery, backup circuits and monitoring.
Remember, your inverter choice might not be the same as mine, and that’s okay. If you’re thinking about a battery though, it’s best to do it on day one. If, for some reason, you still want to wait, draw a line in the sand and write X number of months rather than X number of years; otherwise, you risk being blindsided.
I’d be very keen to hear readers’ inverter choices, and any of your experiences with ‘battery ready’ systems. Hopefully we can help someone who’s currently sitting on the the fence.
About Kim Wainwright
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Hi Kim, I have an AC coupled system using Enphase inverters and a Tesla 2 Powerwall. The downside for me is the losses to convert the AC produced at my panels to DC to charge my battery and then further losses to then convert my battery DC to AC for use in my home.
The biggest advantage with my system and other AC coupled systems is redundancy. My system has been operating for six years. In that time I’ve had separate problems with both the Enphase and Tesla equipment but I have never been completely offline so always producing green cheap power.
I know a few people with the “normal” DC coupled systems. Many have had inverter issues and it has been game over until a new inverter was installed. Can’t speak for hybrid inverters but they would probably be a single point failure source from your diagram. I understand the reliability of most equipment has and is improving but dealing with suppliers, installers is invariably painful particularly when they no longer exists and installation rules have changed
Hi Guy. Redundancy is certainly an issue that’s mostly overlooked. I should have had it on my list as a plus for AC coupled systems. Thanks for bringing it up.
DEYE Hybrid Inverters are my choice as you have the option of a Lead Acid or Lithium battery which means you can use any brand of any battery on the market. I have used the 5KW version for 18 months without any issues.
Hi Max,
How have you found the Deye product? I’ve seen them badged as NoArk as well, albeit with a less comprehensive range. Do they have good surge capacity?
Hi Anthony, I have had no problems with the DEYE product in the 18 months of operation. The main reason I purchased this Inverter was the ability to use Lead Acid or Lithium batteries and not be locked into a proprietary battery system. Other brands include Sol-Ark and Sunsync which I believe are made by Nigbo Deye in China. As far as surge capabilities go, I have had no issues running fridges / freezers and a Fujitsu split system air conditioner. Also, the ability to monitor the system and change parameters remotely is very useful.
I believe the DEYE Lithium battery should be available soon as well which I am very interested in. I think this product needs better marketing to get the word out about the capabilities of this inverter.
Hope this information is useful.
We need more grid-tied inverter options able to use ~48 V battery architecture. LiFePO4 options are way cheaper and easy to add capacity than the over priced Powerwalls of the world.
Hi Alex
The best ones have been available for years in 48v or 120v.
https://www.solarquotes.com.au/blog/selectronic-sp-pro/
I said we need *more* options, not that none existed.
Selectronic is a fine inverter but they are far too expensive and this defeats the purpose of being able to use lower costs batteries.
BATTERY FIRE BIG PROBLEM.
Hi Dave,
Using all capitals in your message indicates you’re yelling and the lack of nuance would also appear to make the comments irrational.
https://support.solarquotes.com.au/hc/en-us/articles/6041404837135-I-Want-To-Charge-An-EV-In-My-Garage-Can-It-Catch-Fire
Mind you I wouldn’t charge an e-scooter or similarly cheap product in my own house.
DNSP limits on per phase connection may make AC coupling a battery a problem later on.
You might put in an 8-10 kW PV inverter only to discover adding another 5 kW battery inverter is not permitted. Not helped when DNSP connection requirements are fluid (they’ve been changing in my area, becoming more restrictive).
Some inverters offer the option to add the DC coupling feature later on. e.g. Fronius Gen24. That way you don’t need to pay for a feature up front until you want to use it.
Hi Alex. Yes DNSP rules have limits for AC coupling too. I’ve tweaked the post to reflect that. Thanks for the reminder.
Hi Kim,
My newly installed system has now been operating for exactly two weeks. I opted for the Fronius gen24 hybrid inverter, 10kW worth of panels and BYD 19 kWh battery stack. The weather has been quite variable with not a fully sunny day but so far the system has been virtually “off grid” with no power drawn, and a little bit exported. I might add that I also charge my car and the only adjustment in my habits is that I don’t charge the car overnight. Since I am retired and mostly at home, that’s not a problem. The point I am trying to make is that it is now well possible to live off grid with a system that doesn’t cost the earth and can provide continuous power from the big nuclear thing in the sky. It may well cost less to install micro grids everywhere than one single earth bound reactor;-)
While a good read and enjoying all the feed back it does seem that it’s not getting easier to install either solar or solar /battery. I understand the need for safety first but really would like someone to make an all in one unit that has everything including the battery ready to connect to solar panels like a computer plug and play.
John here I am not very electronic but I have a regular inverter and added a battery my problems arise from the two are not from the same supply firms,
Once again, this article completely contradicts the advice the Solar Quotes approved installers gave me.
Can I submit an article on all of the bad advice I got recently ? A warning to others seeking advice from “experts” … will not mention any names or companies.
sure send it to [email protected]
A simple thing not to forget is (wall)space for the intended batteries. My brother has just added 6 more 1.9 kWh LTO batteries to a set of 8 already on the wall. Extending the modular busbars is simple – If there’s room in a straight line. Adding the new batteries must maintain equal length (for equal resistance) cables to all the parallelled batteries. The work is dead simple in technical complexity terms, but still costs several thousand dollars for the installer to do all the grunt work, as it still takes time. In this case, they made a model runout offer, avoiding missing out on the last chance for the simplest of upgrades. Handy.
I also have two battery inverters and two PV inverters, but off-grid. Adding more battery can again be done by stuffing more into the battery box feeding the battery inverters. But when bidirectional EV chargers become more economical, then leveraging the 51 kWh in the MG4 would be attractive. It has V2L, which could be fed into the system’s generator input, but it only outputs 2.5 kW or so. That’s enough to keep the fridge going and transfer enough to the house battery to run the microwave intermittently. But the Multiplus II is configured to draw up to 3 kW, so would need reprogramming first.
With at least a 300% oversized array, the 10% yield in medium overcast is still 30% of nominal needs, so dropping EV charging, HWS heating, washing, vacuuming, etc. allows cruising through a week of overcast _without_ dropping the battery reserve much at all. The “5 days autonomy” is more cheaply supported by PV array than by battery size.
Changing stuff costs time, effort, and money. The professionals who drop in to do it may not achieve instant oversight of your system’s peculiarities, so there might be more than one attempt to get it right. Planning is key.
Thanks Eric,
Finding a place for batteries can be a real challenge you’re right.
Hi Anthony,
I have been off grid with a grid connect changeover for the past 15 years and on my second set of AGMs which I am very happy with. I have 12 530amp 6 volt batteries connected for 24 volts with a 5kva Victron inverter. The system runs everything in the house except the electric stove and hot water system. The only servicing I do is wash panels, check panel connections and disconnect and clean battery terminals. Where I live we have had a couple of long term grid outages one 5 days and the last one 2 days. My nehbours use my spare freezer at these times.
Great sense of timing Kim. I am “sitting on the fence” at the moment.
Am about to replace my 8 year old 4.9kW system (Fronius 4.0 and 19 Trina Honey 260s), which has and continues to function seamlessly although not meeting all our demands. Purchased originally through Finn’s Solarquotes process by the way, and has now paid for itself.
We are considering replacing it with a Fronius GEN24 8 and 18-20 Trina Vertex S panels and to add a BYD battery stack. But which GEN24 to go with? I am particularly curious about your comment that hybrid inverters are “more efficient and will marginally convert more solar power into useable electricity”. Do you consider this and, for example, the integrated monitoring big advantages over the string model? I could probably be happy with either!
Read all Solarquotes without exception.
Hi Paul,
Sounds like you’re a fanboi like me, fan cooling is a great refinement. Are you on 3 phase? Can you retain the old system?
I would investigate the 10kW Gen24 because it might allow you a few extra panels down the track when adding 2kW more inverter is impossible. I’m pretty sure the larger Fronius units are all “plus” designation so they come with hybrid ability (and expense) straight out of the box. The nature of any hybrid means you can overdrive them and even though they have hit an export or AC output limit, there’s still DC energy available to charge straight into the battery.
(Kim might have a few words to add as well)
Thanks Anthony very much. Single phase only but that might change after
tomorrow’s meeting with our sparky about whether a possible install of a 90cm induction top cooker means having to go to three. Am giving some thought now to Kim’s suggestion we keep the current system and add another (size??? limited remaining roof space an some intermittent/morning shading). I will have to get my head around a battery install with both?
Hi Anthony, yes true. The Fronius Gen24 – Plus is a downloadable software change only, that the installers will dp for you.
Cheers
Hi Paul. Reiterating Anthony’s remarks, it would be a shame to lose your 8 year young existing system half-way through it’s life. Better to keep it and add another one if you can stay within the DNSP limits.
Re my comment about hybrids being marginally more efficient – it’s actually the DC coupling that’s more efficient. There’s 2 extra conversion processes in an AC coupled system that happen in the battery inverter which sometimes housed within the battery enclosure (AC to DC, and DC to AC). In the Powerwall for example the roundtrip efficiency in the data sheet accounts for this (read the fine print). It’s roundtrip efficiency is 90% compared to say BYD Bbox DC coupled battery at 96%.
That’s not the full picture though as there’s inverter losses, other system losses, and the battery losses aren’t relevant in solar self-consumption. Good luck with that calculation!
Either way, I’d keep your existing system until it dies. That’s a win for the environment and probably for your wallet as well.
Hi Kim, Thank you for your prompt and comprehensive reply. You and Anthony have really got us thinking with respect to keeping the old system and adding another. Not something we had considered given additional roofspace limitations and some early morning (to 9:30ish) shading issues, but probably doable with good design input. Would be nice to have the 440w
Trinas in the best north-facing position but assume best not to disturb the old system placement too much. As for the battery, are there major issues with charging from two systems? I think my DNSP limit is 10kW but will have to check. If so I assume I could have up to a 6kW inverter for the added system to go with our existing Primo 4.0-1. Was essentially aiming for an 8-9kW system overall with our replacement thinking. Happy to stay with another string inverter.
Hi Paul,
I put a 4 & 6kW Primo on my house to get to 10kW.
With a Selectronic SpPro it’s bulletproof but you’d have to find someone with a 6kW snap series primo I think. The Gen24 & Primo won’t talk to each other directly, and they need to be leader/follower configuration if they are both to work during a grid outage.
A 6kW Gen 24 would be good though if the DNSP allows it. May need a SwitchDin droplet for export limiting but the two inverters will show up on the same monitoring platform.
With the exception of Fronius who DC couple a BYD or LG battery, pretty much everyone else of note in the hybrid inverter market now has their own battery. Sungrow, Goodwe, Huawei/iStore, SolarEdge, SAJ, even Growatt.
Every single one of them assures me, several in writing, that their future batteries will be backwards compatible with existing hybrid inverters although some have drawn a line in the sand by saying ‘from this particular model onwards’. And why wouldn’t they? More profit by selling a battery to their installed base.
Oversizing is for me by far and away the biggest advantage of DC Coupling a battery. Most (again, except Fronius) allow 200% oversizing so 10kW (at least) on a 5kW inverter and 20kW on a 10kW inverter. With panels almost free that just makes sense to provide sufficient power to charge up a decent sized battery, especially in Winter.
If people buy a hybrid inverter option they typically pay about $1,000 to $1,500 more than the manufacturer’s ‘standard’ version but that often includes the Consumption meter with the hybrid. That’s the extent of their additional outlay. Come the time for a battery they can go with whatever DC Coupled option available or go for an AC Coupled option instead. Best of both World’s IMO.
AC Coupling a battery is fine as well. I have few arguments against it although it would be nice if they started bundling 3 phase inverters with the battery not single phase, as hopefully that would then allow it to grid form and keep the regular solar inverter alive to top up the battery during an extended blackout.
I’ve found in researching my new system, that there is a difference (albeit small) in efficiency between a grid tied and hybrid inverter (I was looking into Sungrow inverters).
Modelling this over the year results in 15911kWh’s for the normal grid tied inverter and 15820kWh for the hybrid inverter. A difference of 91kWh.
Although this is a small difference, it might be another reason to avoid installing a hybrid inverter just for the ‘chance’ of installing batteries at a later date.
What about 3 phase systems? We are in WA, have 3 phase connected to the house, and I understand that we are obligated to have a 3 phase inverter (except for a very small system).
I also understood that AC coupled 3 phase batteries are few and far between, and may easily violate limits on inverter size.
I am considering installing a “battery ready” system, in case we want to add batteries in the future. Was leaning towards a Fronius Gen 24 just to have the “PV Point” to provide some essential power during the day to critical appliances during very occasional grid outages.
Hi John,
Sounds like you’ve got a good handle on it. Fronius are a great device.
Read here for more
On three phase in WA, you are allowed a 5kW single phase inverter as long as you connect a battery to it. This would typically be a hybrid inverter and battery from Fronius, Sungrow, Goodwe, iStore, SolarEdge, SAJ, Growatt, Solplanet, Solis etc.
3 phase hybrids and batteries are not much more cost but they tend to expose one achilles heel, which is backup. During a blackout the battery power (topped up by solar during the day) is split equally (or very close to equal) across the three phases. This means that with most small inverters (5-6kW) you only get up to 2kW per phase which may not be enough for single phase loads. Less of a problem with larger 10-15kW inverters. It’s also why many people go for a small single phase hybrid and battery on 3 phase because then the full 5kW is delivered, albeit to circuits on one phase only.
AC Coupling a battery in WA can be done with a hybrid inverter as long as the inverter falls within your 15kW inverter limit. If that’s not possible then yes, it’s a bit of a problem. Tesla Powerwall 2 works fine in every regard apart from it can’t keep a three phase solar inverter alive (grid forming) during a blackout to top up the battery. There are a few other AC coupled inverter/batteries from Growatt, Goodwe, Alpha, Franklin, but yes, the choice is limited and the ‘grid forming’ issue is common to all of them.
These do not form part of your 15kW inverter ‘allowance’ because they are not hybrids. They can not connect to solar panels and for Western Power, that’s ok. Bonkers if you ask me considering we have 1.5kW export limiting.