You may have seen inverter companies promoting “battery-less backup” – a feature that lets you power lights and appliances with your solar panels during grid outages and without the need for batteries.
The idea is that with the right electronics, solar systems can provide some backup electricity on sunny days, even without battery storage. Enphase initially rolled out this capability in their IQ8 system microinverters in America under the name “Sunlight Backup.”
Has Sunlight Backup Been Oversold?
In the USA, Enphase has found out the hard way that offering a product with limited capacity sometimes means people oversell it or overload it.
Without batteries to provide energy storage, having a whole house on a system that relies solely on sunshine is a recipe for disappointment because the supply isn’t stable.
Still, Enphase put up a fair warning on their website :
“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.”
What I thought was adorably optimistic was that they even offered a generator integration. Having done 15 years of off-grid systems, I can assure you that the generator is always the source of problems.
Even though it was never offered in Australia, there were ambiguous web links on the Australian website, creating consumer confusion. Where it was released on the US market, it has now been withdrawn, though references to it are still floating around on their American website.
How Sunlight Backup Was Supposed To Work
Sunlight backup leverages tiny storage capacities in the capacitors built into solar inverters. Think of a solar system like a set of bagpipes – small breaths inflating the “bag” is just like fluctuating sunlight, charging the capacitors, building a reserve of energy. Small demands – like lights, the clock, and devices in standby mode – can tap that stored capacity like the humming “drones” of a bagpipe.
But firing up a large electric load, like a fridge, creates a sudden, significant energy demand – the equivalent of plunging a knife through the “bag”.
The surge needed to start a motor can completely drain the capacitor reserves instantly. Without a battery’s hours of storage to draw from, the system struggles to catch up, leaving the fridge and other appliances with a series of brownouts instead of steady power.
You Need Batteries For Proper Backup
Small capacitor storage as a buffer helps manage normal fluctuations in solar input versus energy use. But for critical loads like large refrigerators, sunlight backup systems risk rupturing that delicate balance between supply and demand. Repeatedly forcing large appliances to turn off/on can damage them.
That’s why companies like Fronius stress that their inverter’s emergency solar powerpoints (Fronius call it “PV point“) are for small essentials only – such as recharging phones, not for attempting to power an entire house1.
Backup systems paired with batteries provide the necessary stability. The stored energy acts like a shock absorber against the spikes in demand that could wreck unbuffered sunlight backup capabilities.
The Verdict: More Novelty Than Reliable Solution
Customers have always asked why solar doesn’t work during an outage. The answer is that you need the grid to give the system guts. In the end, while sunlight backup represents creative innovation in solar technology, the concept has proven more of a novelty feature than a practical solution.
The best use-case for battery-less backup is via a single ’emergency powerpoint’ next to the inverter (available with SMA and Fronius Inverters). During an extended outage, the household can recharge phones, torches, and power tools because they all contain Sunlight Backup’s essential missing component – a battery.
Relying on instant solar production rather than batteries can never provide reliable backup. Battery integration remains critical for systems tasked with essential loads during grid failures.
The thought of backup without expensive batteries has always sounded too good to be true. Turns out it is.
A Note On Enphase’s Australian Support
I’ve been critical of Enphase recently, but I just wanted to thank their tech support team in Australia. When I had a query, it was great to get a knowledgeable human answering within 6 minutes. Better yet, when I’ve got some nitty gritty points to ask, the Australian technical support manager is still happy to answer calls, despite my last whinge.
About Anthony Bennett
RSS - Posts
Yep seen this advertised and could only assume they must have rather large caps with some fancy electronics to limit drawn down.
However is there any Battery-Capacitor units that could work with say 2 kWh storage?
I was curious about Sunlight Backup, but never explored it further as I had no desire to be a pioneer consumer. But I do have an Enphase system, and would say that Enphase tech, coupled with a qualified and competent installer, has been a rewarding investment, on a purchase that I was hyper-nervous going into. So I guess this is simply a counterpoint about Enphase to provide offset and balance to Anthony’s experiences.
I have Whole Home Sunlight Backup installed in my home. I have never really tested it under extreme load startup, but perhaps I should and publish my findings.
Yes you can:
Design a simple and very robust cost effective solution, to exploit the Enphase “Off Grid” Micro Inverter Capabilities without requiring another inverter [battery + inverter].
For each Micro Inverter installed; design a simple DC Coupled [parallel connection plus charging control circuit module] to a properly sized custom battery stack, with the resultant single DC output connected to the Enphase Microinverter DC Input.
Job done.
This is pretty much the same design principle as a DC Coupled Off Grid System. Been happening for years.
The key point that brings it together is the seamless connectivity and functionality of the highly efficient DC Coupled design.
And this may be why Anthony after 15 years of Off Grid experience didn’t reflect on this point because I am assuming his experience was focussed on AC Coupling designs.
The strength looking forward with this system design is that it is extensible and can also accommodate the Grid Connection; and with some other simple sensors and controls integrated, can become a solid “24/7 smart power plant solution”.
PS. Off Grid Solutions designers are well versed in dealing [through sensors and controls] with alternative power source equipment and designs for times when they might be needed for momentary or specific purpose power requirements by the main Off Grid System.
Lawrence Coomber
Hi Lawrence,
I had to read that passage twice but I’m still curious to ask exactly what you’re proposing. I mean I’ve seen micros rigged up as a nifty constant current load to discharge test a 48v battery… and I’ve built, maintained, reconfigured and updated DC coupled power systems since I was playing with 32v lighting sets 35 years ago.
Are you thinking of a single DC bus connected to a battery, with all the micros drawing from it? Enphase do that and put it in a box on the wall I’m pretty sure. (Finn quips that when all you have is hammer (or micros) everything looks like a nail)
Or are we talking a stack of individual little batteries, all wired in parallel to respective individual microinverters, and individual MPPT charge controllerssharing the energy from the respective PV panels?
With redundancy and individual monitoring, Enphase certainly have some benefits, but simplicity isn’t one of them per se. When you add the sheer number of connections and component, plus powerline communications, it’s superficially simple but there’s a lot more to enphase than meets they eye.
That’s the problem with making assumptions when you’re not completely across the technology. What appears straightforward can actually be quite difficult to both execute and meet standards.
Do you think we will ever end up with an “islanding” capacity?
Hi Ron,
We already have it. Take a look at the way Fronius or SolarEdge hybrids are connected to the swichboard using parallel connection and a “backup box” to island the house from the grid.
https://www.solarquotes.com.au/blog/powerwall-alternatives-hybrid-inverters/
Cheers
It seems to me that we need a smarter battery setup. We live in the country and we often have blackouts while the sun is shining. It seems to me that at that time you want a battery with a relatively large amount of kW, but relatively small kWh, the sole purpose of which is to smooth out the fluctuations in supply and cater for the startup of the larger appliances. Similarly, I would like to have a battery on the critical circuits that would have a relatively small kW capability but would last a significant time ie large kWh, Finally, I have a heat pump on the spa and a number of air conditioners. It shouldn’t be so difficult to actively manage them so that supply and demand was balanced.
I have not yet found an electrician that doesn’t consider this way too difficult.
Am I being unreasonable?
Hi Adrian,
Firstly, the main grid in Australia is reliable, 99.998% by law in fact.
If you really look into reliability… as more renewables are deployed the grid reliability only goes up. It’s so obvious even the Liberal party is claiming credit for it… how the wheels turn.
https://reneweconomy.com.au/five-years-after-blackout-south-australia-now-only-state-with-no-supply-shortfalls/
Secondly, lithium batteries aren’t disismilar to capacitors when you compare them to lead acid batteries traditionally used in off grid power. If you get some lithium titanate cells they’re excellent for surge capacity and charging speed.
Zenarji make them in Australia and you’ll need a Selectronic SpPro to go with them. Most people aren’t keen to spend enough money though, despite being supporters of local manufacturers they seem to develop short arms and long pockets when you mention it’s available.
Thirdly you can certainly have smart management, I’m told that Home Assistant is the go to architecture for those who have a DIY bent for software. There are proprietary solutions using internet connected services like google and amazon as well.
Many heat pumps have DRM control terminals so that makes it pretty easy.
Cheers
Adrian:
Of course you are not being unreasonable:
Your question is a simple one to put to an experienced Power Generation Plant Designer | Integrator | Installer, who specialises in these technical areas.
You have in fact answered your own question by stating “I have not yet found an electrician that doesn’t consider this way too difficult.” That surely must tell you something.
Most CEC Licenced practitioners ensure their earnings potential by not moving much beyond the traditional boundaries of simply Installing Total Solutions hardware [solar PV Modules; Inverters and Batteries] imported from elsewhere, by following steps 1 to ? as described in the supplied installation manuals; and that is in practical terms, the full extent of their commercial interest; skills; qualifications; and experience.
The System Designer Integrator Installer you are interested in, will not come from this pool of expertise as it currently stands.
You will have to search wider to find those skilled and experienced design engineers to get an integrated solution.
Regarding your own brief System Design assessment; I understand what you are thinking in general terms [well done for that] but you have not [and quite understandably) described a practical and optimised solution, by a long way.
Despite that, I appreciate your comments and views and they are very important for the broader Australian Industry Practitioners to focus on moving forward.
I am a member of the Australian Govt. Technical Advisory Committee over the last 2 years in rewriting the Electro Technology Apprentices Training Scheme which came into force in July this year. It is a total rewrite and rethink in training in Australia and has a very heavy emphasis on remediation of all of those key points I have mentioned above.
Lawrence Coomber
Thanks Anthony:
By Enphase’s own admission, the Micro’s [Backup – no Grid] functionality is problematic at best and useless at worst, and designers and system users should not get fixated on it being all that reliable and practical. So any further discussion about that subject becomes more theoretical than practical from an integrators point of view.
Moving it forward one step, and summarising the key technical points though, reduces the design imperatives to: where should the battery stack [or stacks] as may be the case, be best configured in the overall circuit design? Should they be DC Coupled to emulate the solar PV Array or emulate the PV Module.
You have already touched on these points.
I always opt for higher voltage lesser current system designs where possible, for system safety, and considerable cost savings in copper wire and circuit protection devices, etc. Other system efficiencies are well known.
Lawrence Coomber
Speaking of Enphase support. Early this year, I finally phoned Enphase one morning to ask them to update the firmware on my Envoy S, so my phone’s Enlighten App and web portal could display Live Status.
After a few checks, the Enphase tech stated that he would attend to the update/upgrade later in the day and to check the App/portal later in the evening.
I check my Enlighten app frequently. So imaging my surprise when the update was completed in a couple of hours and I could view Live Status. Thanks for your prompt customer service, Enphase.