Solar Backup Without Batteries: Revolutionary or Ridiculous?

Battery-less backup

Solar newbies are often bemused as to why their rooftop solar shuts down during a grid outage. It seems counterintuitive, given that the idea of an alternative power supply is to generate electricity separately from the grid.

Installing a home battery is the obvious solution to keeping your lights on during a power cut. However, the cost of batteries puts them out of reach for many people.

A handful of solar inverters offer a seemingly magic backup power solution: backup power without a battery during a grid outage.

It sounds too good to be true, and you know what they say about that.

This article will highlight some inverters with this feature and explain their limitations. We’ll also discuss why it’s rare and whether you should even bother about it in the first place.

Why Does An Inverter Shut Down During An Outage?

All solar inverters are not equal. The one thing they have in common, and their primary function, is to convert DC (direct current) from solar panels or batteries into AC (alternating current), which is usable for household appliances. That’s where the similarities start and finish.

“Grid-following” inverters are the most common type used in grid-connected systems. Their AC output is designed to synchronise with the electric grid, ensuring the generated electricity is in phase with the grid’s electricity. The inverter typically shuts down when there’s a blackout or a power outage.

All inverters must disconnect from the distribution network whenever the supply is disrupted. If your inverter kept putting electricity into the grid, it could electrocute lineworkers who are trying to get you back on line.

Backup With A Battery

Adding a battery can provide backup capability during a blackout. There are many configurations and levels of battery backup available. However, in all cases, the inverter must still be able to disconnect from the grid during an outage.

In this scenario, the type of inverter used depends on the system’s setup. It could be either a hybrid inverter or a battery inverter. These inverters can switch modes – from being connected to the grid to operating independently as a backup. Once switched, the inverter provides a steady voltage and frequency, but only to a limited extent, powering emergency circuits from the battery. During this time, it remains disconnected from the main power grid

Can Solar Panels Supply Power During An Outage?

Yes, sometimes they can, but a battery is a crucial component. The battery has storage capacity and acts as a buffer. Relying on solar panels without a battery to power your appliances is skating on thin ice.

Most inverter manufacturers don’t offer “backup without batteries” as a feature, and even when possible, they certainly don’t make a song and dance about it. I think it’s for good reason. They don’t want to be setting you up for disappointment and damaging their brand in the process.

Stating the obvious – solar panels only generate power in the daylight. So that’s about 50% of the time you will be sitting in the dark. Also, their generation capacity changes instantaneously. The available power to supply loads is as variable as the weather. One minute, it’s there; the next, it’s gone. Is that what you call “backup power”?

Some electronic devices can be damaged by being switched off and on repeatedly over a short period, and many electric motors and compressors simply won’t start up without enough capacity to support their inrush current. One could argue that for the low-powered devices where this may not be an issue, you could spend your money more wisely for so-called “backup”.

So, having poo-poohed the concept of “backup without batteries”, without further ado, in no particular order here are some inverters I’ve found that will do it. There are most likely more to add to this list, but they’re keeping their heads low. Please let me know if I’ve missed any.

Inverters With “Battery-less Backup” Available In Australia

Fronius GEN24 Plus

Fronius hybrid inverters offer two levels of backup. “Full backup” requires a battery and “PV Point” (battery optional). You’d be hard-pressed to find the word “battery” mentioned in their PV Point blurb, but I dug deep. The following is an excerpt from the freely available installation and commissioning document entitled “Application Guide PV Point Fronius GEN24 Plus Series”:

“The PV point represents the basic emergency power function of the GEN24 Plus series and is integrated as standard ex-factory. It is a socket that is only supplied in case of grid outage based on the currently available PV generator power (or available battery). The switch happens automatically by the inverter and doesn’t require any additional grid separation components. Every important single phase consumer in the household up to 3 kW can be supplied by the PV point. A PV point installation does not (necessarily) require battery storage – an installation of a storage unit is optional.”

Fronius PV Point

Fronius PV Point – this graphic shows a European socket powered from the PV Point. The Australian version requires an electrician to hard-wire a socket outlet from the inverter to make it work. You’ll also need to provide an RCD (type A 30 mA), so add that to the bill.

Delta E5

The Delta E5 is another hybrid inverter that offers a battery-less backup feature. The datasheet states a capacity of up to 3600 VA when in “standalone mode”. It will also need a separate distribution panel with RCD protection for backup loads.

“The stand-alone function of the Hybrid E5 inverter allows the owner to use the battery to power critical loads when the grid is not available. This function will activate automatically during a power outage, although the E5 also has a button to manually switch the system to stand-alone mode. The inverter is still able to enter stand-alone mode even when the battery is not connected, as long as there is sufficient PV production to power the loads.”

The video below demonstrates how the Delta E5 can “deliver your solar power to your home during a blackout without a battery” or maybe just heat up last night’s spaghetti leftovers for lunch on a good day.

Huawei SUN2000

Although there’s nothing written in the official documentation about the Huawei hybrid inverter’s functionality regarding backup from solar PV only, it can certainly do it. The video below clearly shows the inverter in conjunction with a “backup box” supplying power to a porch light during daylight hours with the main switch and battery turned off.

The single-phase backup box is limited to 5kW, and the three-phase box is to 3.3kW on a single phase. Note that Huawei solar inverters, batteries and other solar products in Australia are now re-branded as iStore. I would assume that all functionality is the same.

“Battery-less Backup” Unclear Or Not Available In Australia

SMA Sunny Boy TL-US

It’s just as well that SMA‘s audaciously named “Secure Power Supply” doesn’t seem to be available on Australian models. Their tech tip on the USA website states:

“SMA’s Secure Power Supply is the easiest, most cost-effective way to provide opportunity power during daytime grid outages without costly batteries.”

Yet their installation document, “Connecting the switch and outlet for secure power supply operation” wins oxymoron of the year status for this doozy:

Secure power supply operation must not be used for loads that require a stable electricity supply. The power available during secure power supply operation depends on the solar irradiation on the PV system. Therefore, power output can fluctuate considerably depending on the weather or may not be available at all.”

Some websites quote up to 2000 W capacity, while others say 1500 W. In what looks like typical American oversell, the USA site has a webpage aimed at salespeople entitled “How to explain Secure Power Supply to homeowners.”

SMA Secure Power Supply

Presenting the solar oxymoron of the year – SMA’s “Secure Power Supply”, which shouldn’t be used for loads that require a stable electricity supply!

SolarEdge Backup Interface

There’s nothing official forthcoming about battery-less backup from SolarEdge. However, I found one interesting third-party FAQ site that hinted it might be possible:

Q: Can the Energy Hub and Backup Interface provide backup without a battery (PV-only)?
A: No. Although the system may operate, it is not supported, and results will vary.”

Growatt SPF ES Series

This popular DIY solar power YouTuber in the USA gets pretty excited when he tests the Growatt SPF 3000TL LVM-ES off-grid inverter and finds it can power his portable air conditioner without being connected to a battery. It should get us here in the land of Oz less excited because it’s not CEC-approved. However, the SPF 3500 ES and SPF 5000 ES are CEC-approved, but it’s yet to be clarified if they have the same functionality.

Sungrow SH Series

At least three Australian websites claim that the integrated backup on these hybrid inverters will support an emergency power supply directly from the solar panels in a blackout if enough power is produced (even without a battery). However, there’s nothing officially from Sungrow about this, and nobody’s been brave enough to post a video yet.

Enphase IQ8 Sunlight Backup

In 2021, Enphase launched the IQ8 microinverter with a lot of fanfare, enabling solar-only backup during grid outages. The following statement is from their USA website on release day:

“Unlike competing devices, IQ8 is capable of forming a microgrid during a power outage using only sunlight, providing backup power even without a battery.”

Their Enphase Sunlight Backup User Guide states the obvious:

“NOTE: Sunlight should only be used for the essential loads in the home. Using the solution to backup the entire home will lead to poor experience and is not supported by Enphase.”

The statement doesn’t go far enough, considering backup solutions rarely support the whole house, even with a battery. It’s a moot point anyway because, apparently, it was never offered in Australia, and the word is that since it was released on the US market, it has been withdrawn. As far as I can see, there’s no official line on that.

Backup – There’s No Such Thing As A Free Lunch

While the allure of “battery-less backup” from solar inverters during a blackout seems appealing, it’s essential to take a deep breath and approach cautiously. There’s no such thing as a free lunch. And a word of warning – be wary of solar companies overselling this feature without a clear explanation about the limitations. It’s not what they say but more about what they don’t say.

About Kim Wainwright

A solar installer and electrician in a previous life, Kim has been blogging for SolarQuotes since 2022. He enjoys translating complex aspects of the solar industry into content that the layperson can understand and digest. He spends his time reading about renewable energy and sustainability, while simultaneously juggling teaching and performing guitar music around various parts of Australia. Read Kim's full bio.

Comments

  1. Excellent piece, thank you. if one doesn’t already exist, I’d love more details on the whole concept of ‘grid-forming’ in general, what it takes to create a grid and keep it stable, including frequency, inertia etc. And how renewables are changing some of the thinking around all of that. I know a lot of it is very technical electrical engineering!

  2. Andrew McDonald says

    Hi Kim,
    Thank you for this well-researched and helpful article. You have identified almost every solar home owner’s frustration. “Why have I got no electricity when the grid is down and the sun is shining”.
    I was unaware that so many brands had some form of “emergency power generation” for grid outages. Clearly, manufacturers are listening to customer complaints.
    Hopefully, 2024 will bring more exciting developments in this area, particularly for three-phase homes and for people who would like a UPS function for essential circuits.
    Thank you again for your helpful explanations.
    Best wishes,
    Andrew

  3. I strongly suspect that more people, especially in rural areas, will find the money somewhere to get battery backup.
    There are PLENTY of people in the Gold Coast hinterland who have been without power since Christmas Day. In some areas the grid was effectively destroyed, and needing to be rebuilt from scratch.
    I know someone there with a Powerwall. He has had no issues since he lost his power, just needing to be a bit cautious on A/C use when the sun is not shining.

    • Like I’ve said to several friends, don’t tell me panels and batteries are expensive when you’re towing your $125,000 caravans with $120,000 4WDs. I’d love to see the ROI on those.

      • Hi,

        A bit OT, but:
        Our car & ‘van are nowhere near that price, but never expect a ROI (though I’m sure we’d be able to sell once we’re finished caravanning). We both consider that they are better than staying in hotel or motel, probably a BnB as well. My sisters and their husbands go on cruises & other holidays, I would think they’ve probably spent nearly as much as us, even counting caravan park & fuel costs. Also, we can go whenever, and wherever we want.

        I have an inverter that will run “batteryless”, and have done so once, when the battery was unusable due to a faulty BMS. It was OK during the day. I would not recommend it for long term usage. I now have 2 batteries. Just in case.

        Our system has paid for itself after 13 years, even though my wife didn’t believe that it would when installed (solar first, then batteries). I doubt that it would pay back as quick if I’d installed one now though because the Victorian Service concession ended late last year, and the PFiT ends this year.

        b0b

      • Reality shows most “grey nomads” use mainly dual cab 4wd vehicles costing (new) in todays market 50 – 60 K dollars, and vans costing in the same market 75 – 90 k dollars. With overnight park fees approaching $85.00 plus in coastal areas the use of solar and discreet off road parking the cost benefit ratio is IMMENSE.

        Stick to the issue/s under discussion.

        • This is the issue under discussion, much of the obstruction to renewables is a belief that the cost of living means people can’t afford it. If doing so much travelling that having your own van and a vehicle to pull it allows for full cost recovery was the problem ordinary non-retired Australians needed solved, then I’d agree with you. It’s not though, they face the challenge of feeding families and keeping the lights on.

  4. Warren Harvey says

    Been without grid power for about 25 years and can’t understand why townies don’t shaft the big power companies and tell them to take hike.

    We only have a 3.5k system with battery backup, and while it requires a little thought when we use electricity, we still manage to do pretty well with everything we want to do with it. Just have to work a little smarter and that isn’t a bad thing by any means.

    There are far bigger systems today for a lot less cost than we first paid, which ought to please almost everyone when it comes to power hungry appliances, even electric stoves and air-conditioners.

    On balance, we’re way ahead of the charges electricity companies apply to their town customers and it’s quite possible (if we can swing it) we may even forego moving to a town for retirement purpose due to the cheaper power costs we’ve become so used to.

  5. Adam Watts says

    Question. As someone with 3 phase power, it seems almost impossible to find an AC coupled battery that would provide “apocalypse proof backup” ie charge an AC coupled battery from a 3 phase solar inverter during a grid outage. Could the Fronius Gen24 Symo (3 phase) overcome that by charging a single phase AC coupled battery via the emergency power outlet during a grid outage?

    • Anthony Bennett says

      Hi Adam,

      I have seen this idea mooted as a way to get battery back up on the cheap. Using the PV point function to run something sensitive like a fridge, which has a large in-rush current and probably wouldn’t appreciate being turned on and off all the time by the clouds. A 3000VA UPS system (designed to back up a computer) or perhaps a “camping battery” would be a reasonable way to buffer the intermittent output from a PV Point into something that is more reliable and could last through the night. We’ll have a new post out on three phase battery backup very soon.

    • Tini Steinmann says

      The Fronius Symo GEN24 8 & 10 kW combined with BYD Batteries will provide stable 3-phase back up power.
      As will SMA STP Smart Energy inverters with BYD.

  6. Can you have a petrol/diesel generator and a grid disconnect switch and the solar inverters would still see the grid as being there because the generator is providing a “grid” like power?

    Where does the excess pv power go if your not using it all and have a generator hooked up like this?

  7. Robert Epps says

    When we had our solar installed three years ago, we were told an option was to add a “small” battery just to allow usage during the day if the grid goes out. Not enough to get through the night but at least keep the fridge/freezer on etc.
    I can’t remember the specifics but I’d imagine a 3kwh battery would suffice and wouldn’t break the bank. We’re in the Sunshine Coast Hinterland and get occassional outages, especially after a storm. It’s frustrating sitting there with no power while the sun is beaming down on our 10kw array! I’m seriously considering at least a small battery just for these occassions

  8. Question, does the goodwe ET 3 phase inverters have this Function? Officially or not?

  9. Even though the power is unreliable, I’m sure most people would appreciate the feature. It obviously isn’t ideal for running a TV or most other appliances as frequently turning them on and off could cause some components to fail, but it would be handy during power outages for things like turning lights on, turning on the fan in the bathroom and electric cooking and I can’t really see it adding much to the cost of installation, unlike a battery where the additional cost is significant.

  10. geoff brookes says

    I watched the 2 videos re; backup during a grid outage.
    The first guy showed he had enough power to reheat his
    spaghetti and the second proved that it was working when
    his porch light came on. (Prob. a 10W LED bulb.)

    When they can show enough power is available to power
    a 4kW aircon plus other household items without a battery backup
    then I will be impressed.

    Also I will comment that Pb/H2SO4 (lead acid) batteries are ugly,
    heavy, etc. but still work. That’s one of the reasons you have one under
    the bonnet or seat in your car.

  11. geoff brookes says

    Robert,

    Most EVs have at least a 50-60kWh battery. Some have 100kWh
    (or more). You will find, with time, that a lot of EV owners will be
    replacing their batteries when they get below 80% of the output that
    was originally available. That does not mean that all of the batteries
    are not working.

    A lot of people believe the internet talk that these batteries
    constitute a fire risk. If you are one of those then put your battery bank
    in a shed / chicken coop or other outbuilding.

    I reckon the guys that take advantage of the “exhausted” battery packs
    will be those mechanics etc. who have access to these “disposed”
    batteries.

  12. ROGER BROWNING says

    Surprised that no one has mentioned Enphase micro-inverter system linked to Enphase IQ 5 Battery. Recently experienced a four hour blackout where system powered internet / fridges / tv / home phone / all lights /ceilling fans seamlessly until mains power returned. Did not use aircon as length of blackout was unknown. Effective back up for less than $10 k plus nightly saving that battery provides.

  13. I’ve got a 10 kW Growatt inverter, being fed by 12.5 kW series of panels, with a 13.5 kWh/5kW Powerwall2. Unfortunately the Powerwall can’t play nice with the GroWatt inverter, so when there is a blackout the batteries run down until dead, and then we lose power even if the sun is blasting on the panels. If I got another powerwall2 I think I’d be able to get it to work, as the GroWatt output would no longer overwhelm the PW2. Live and learn I guess.

  14. Paul Williams says

    FYI: The Sungrow Hybrid range SHxxRS and SHxxRT models, are supposedly able to do solar only backup also. If the backup mode functionality is enabled in the settings (without a battery).
    Speaking of Sungrow the new 3-phase models SH15T/20T/25T (15, 20, 25kW), are apparently going through the Aus approval / certification process, and are expected to available around mid year.

    • Anthony Bennett says

      Cheers Paul,

      Sungrow admit it’s possible but they don’t actively promote that capacity. Everyone is waiting with baited breath for the bigger Sungrow units.

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