A grid-tied solar system without a battery stops generating the instant load shedding starts, and it stops by design: the inverter must disconnect when it can no longer see the grid. The one test that separates one system from another is not the number of panels on the roof, but whether the inverter can run in island mode, supplying your essential loads while the municipal supply is dead. Grid-tied, battery-ready, hybrid and AC-coupled backup are simply labels placed on either side of that line.
I was in my own kitchen at 20:02 on a stage 4 night, torch in hand, listening. That is the part nobody tells you to do. When the grid drops, a grid-tied inverter does not just go quiet. A relay inside opens with one hard click, the fan winds down over about a second, and then the house is properly off. The fridge compressor stutters, the router light fades, the microwave clock goes blank. That click is the whole question compressed into a single sound.
If you have heard it, you already know where your system sits. If you have not, and the lights stayed on while the street went dark, you own an inverter that can carry a load on its own.
Island mode is the only question that matters
Ask whether the inverter can operate in island mode. Not "is it hybrid". Not "is it battery-ready". Not "can it take panels". Island mode means this: with the municipal supply absent, can this box create its own 230 V reference, hold a stable frequency, and run a circuit until the battery is flat or the sun comes back?
That is the dividing line, and it is a technical one, not a marketing one. Most grid-tied inverters are grid-following machines. They push current into a voltage source that already exists, matching its frequency and phase. Take the grid away and there is nothing to follow, so the inverter has nothing to do. It is not being lazy or badly made. It is doing exactly what its firmware was written to do.
There is a second reason, and it is a legal one in South Africa. Grid-interactive inverters must meet NRS 097-2-1 for disconnection and anti-islanding before they may be connected to a low-voltage network. Anti-islanding exists because a line worker up a pole must never find a cable live from a house he cannot see. Your inverter going dark during load shedding is not a fault. It is compliance.
Where each configuration actually lands
Grid-tied with no battery
Panels, a string inverter, no battery. There is no energy store and no island capability, so load shedding means the system is off. This is the cheapest and simplest arrangement, and it is honest about what it does: it lowers your municipal bill while the grid is up. It does nothing at 20:00 on a stage 4 night. Nothing.
There is a variant that trips people up badly: a grid-tied inverter with a battery attached for self-consumption, peak shaving or storing cheap solar for the evening. It still shuts down with the grid, because there is no backup output and no island mode. The battery is there to shift energy, not to carry the house. I have watched someone discover this after paying for a battery, standing in the dark next to a fully charged pack.
Battery-ready is a promise, not a capability
Battery-ready means the inverter was built with a DC input and a communication port so a battery can be added later. That is all it means. Whether the unit can island depends entirely on the specific model. Some battery-ready inverters have a dedicated backup output and a changeover relay inside. Others will happily cycle a battery for self-consumption and still shut down when the grid fails. Two boxes with the same words on the carton can behave in opposite ways at 20:00.
Hybrid: the one-box answer
A hybrid inverter puts a battery inverter, a solar input and an AC transfer path into one enclosure. The municipal supply passes through it, and when that supply disappears, the transfer path opens and the battery inverter takes over a designated backup circuit. That is the click you want to hear: the same relay sound, but the lights stay on.
Hybrid is the neatest arrangement and usually the least compromised, but it comes with limits that are easy to miss. The backup output rating is often lower than the inverter's headline rating, and much lower than what it can pass through from the grid. A unit that passes 8 kW of municipal power to the house may only be able to serve 5 kW continuously from the battery, and less for a second or two when a fridge compressor or a borehole pump starts. Put a kettle and a geyser on that circuit and you will find the ceiling fast.
AC-coupled backup on an existing system
An AC-coupled backup inverter is added alongside an existing grid-tied system to serve a separate essential-loads circuit, without replacing the original inverter. The old string inverter stays on the wall.
Here is the part most explanations skate past. During an outage, that original grid-tied inverter usually stays off, because nothing has told it the grid is back. Your panels can be sitting in full sun while the battery does all the work, and you can burn through stored energy on a perfectly clear day. Some backup inverters can nudge the PV inverter back into production by shifting the frequency on the backup circuit, and some cannot, or only under certain settings. If you are adding a battery inverter to an existing array, that is one of the first things to establish, because it decides whether your solar is useful during load shedding or simply parked.
The limits nobody puts on the quote
Three things decide how a backup system feels in real life.
Transfer time. The switchover from municipal supply to battery is measured in milliseconds, but it varies. Desktop computers and fibre routers usually ride through it. Cheap clock radios and some older appliances reset. It depends on the unit and on what you have plugged in.
State of charge. A battery held at a reserve for backup behaves differently from one cycled hard for self-consumption. If the pack is sitting at 25 percent at 18:00 because it was doing evening load shifting, your two-hour slot may become forty minutes. The reserve setting is a decision, not a default.
What is on the circuit. Almost nobody puts the whole house on a backup output. The essential loads sub-board, the one a contractor installs separately, usually carries lights, the router, the fridge, the TV corner and a few plugs. The geyser and the stove are left off on purpose. That is not stinginess. It is arithmetic.
NRS 097-2-1, SSEG and the paperwork that follows the inverter
Every grid-interactive inverter in a South African home has to be able to disconnect and stay disconnected, and it has to prove it. That is what the NRS 097-2-1 test report is for. Your municipality's SSEG application process will ask for it, along with the installation signed off under SANS 10142-1 by a qualified person. A hybrid with a backup output does not escape any of this. It is still connected to the municipal network, so it still needs the same approvals, and the metering arrangement has to match what the system can actually do.
What I ask before anything gets signed
I want four answers in writing, and I want them off the datasheet rather than off the salesman's tongue.
- Does this inverter operate in island mode, yes or no?
- Is there a dedicated backup or essential-loads output, and what is its continuous and surge rating?
- When the grid is down, does the existing PV keep producing, and what controls that?
- Which NRS 097-2-1 test report covers this model, and who handles the SSEG submission?
If the answer to the first one is vague, nothing else on the list saves you. Off-grid, hybrid, battery-ready and backup-ready are used loosely enough that the words themselves carry almost no information. The behaviour at the relay does.
The next time the schedule puts you at 20:00, stand in the passage and listen. If the fan keeps running and the microwave clock holds its time, you are on the right side of the line. If the house goes quiet, no number of panels on the roof will change that, and no amount of battery capacity behind a grid-following inverter will either.
