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 Where it was released on the US market, it has now been withdrawn, though references to it are still floating around on their American website.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.