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 many 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 may1 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 the the fence.
Footnotes
- Depending on other factors such as back-up circuits required and whether they are pre-wired during the solar install. ↩
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