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 – 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.”
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.
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