Without an explicit emergency power function, even a house with a solar system and full battery switches off in the event of a grid outage – for safety reasons. Anyone who wants to be supplied during an outage needs a system capable of emergency or backup power with its own wiring, planned from the outset. Realistically, selected circuits then run: light, fridge, router – not the cooker and not the heat pump. (As of: July 2026)
Key points in brief
- The outage reflex of every solar system is to switch off: the inverter automatically disconnects in the event of a grid outage – to protect the people working on the grid.
- Emergency power and backup power are two different expansion stages: the socket on the battery for individual devices – or the automatic switching of entire circuits.
- Whether the system can recharge the battery in island mode is determined by the system: not every emergency power solution can do it, and without recharging, it is over after one battery charge.
- The function costs a surcharge and its own wiring – retrofitting is complex, planning from the beginning is cost-effective.
- Honest classification: the Swiss electricity supply is very reliable – emergency power is a conscious priority decision, not a must.
Why does the solar system switch off during a power outage?
It is the question that reappears with every media report about a blackout: «But I have a solar system – why am I sitting in the dark?» The answer is not a design flaw, but a protective function: in the event of a grid outage, the inverter automatically disconnects the system from the grid. If it were to continue feeding in, there would be voltage on a line that the utility has just declared dead – a danger for everyone working on it.
The same applies to the home battery: in the standard case, it too falls silent with the grid. A full 10 kWh battery in the basement is of no use during an outage if the system is not explicitly built to disconnect from the grid and build its own small island grid in the house. Exactly this ability – to disconnect in a controlled manner, build up voltage itself, supply consumers – is the emergency power function. It is its own technical equipment with its own wiring, not a tick box in the app.
Emergency power or backup power: two different expansion stages
The terms are mixed up in everyday life, but what is meant are two solutions of differing complexity – the exact designation varies depending on the manufacturer, the principle does not:
The emergency power socket is the simple stage: a separately wired socket on the battery or inverter that supplies power in the event of a grid outage (sometimes after manual switching). You can specifically operate individual devices on it – fridge, mobile phone charger, a lamp. Unspectacular, but exactly what many households actually need in an emergency.
Backup power is the comfortable stage: the system detects the outage, automatically disconnects the house from the grid and continues to supply defined circuits – in the best case so quickly that only the microwave clock blinks. This requires a switching device in the meter box and planning of which circuits belong in the emergency programme. This is the solution people mean when they say: «The lights should stay on at our place.»
The difference in effort is considerable – and it explains why «emergency power capable» in the brochure deserves a follow-up question: which stage exactly, with what power, automatic or manual? In the quote this should be named precisely.
What realistically runs during an outage – and what does not?
Here the advertising world is separated from physics. A home battery delivers a limited output – and that decides what can run at the same time:
| Realistically runs | Does not run or only with a special design |
|---|---|
| Light, router, mobile phone charging | Electric cooker, oven |
| Fridge and freezer | Heat pump (starting currents, continuous output) |
| Heating control/circulation pump of an existing heating system | Wallbox / e-car charging |
| Small medical devices, alarm system | Boiler, washing machine, tumble dryer |
Typical classification for home battery emergency power, as of: July 2026 – the output and design of the specific system are decisive.
The art of backup power planning therefore lies in the selection: which circuits belong in the emergency programme, which deliberately stay out? Anyone who wants «simply everything» needs a significantly larger (and more expensive) system – and then usually finds out that the cooker remains pasta-free on a candlelit evening anyway. Added to this is the question of capacity: an emergency power reserve in the battery needs to be planned in – what is held back for the outage is missing for the daily self-consumption work.
Does the system recharge the battery in island mode?
The decisive question for longer outages – and the most frequently overlooked: can the solar system continue to produce while the house is running in island mode?
The simple emergency power solutions often cannot do this: they supply from the battery, but the solar system remains switched off. Then the rule is: if the battery is empty, the outage has also arrived in the house – with a full 10 kWh battery and economical consumers, after quite some time, but still definitively.
Real island mode systems («black start capable»), on the other hand, build their own house grid, in which the system continues to produce during the day and recharges the battery – the house then functions self-sufficiently for days, as long as the sun plays along. This is the premier class, with corresponding requirements for the inverter, battery and electrical planning.
For the consultation this means: do not just clarify «emergency power yes/no», but explicitly «does the system recharge in island mode?» – the answer separates the one-evening solution from the multi-day solution, and it is rarely written in bold in the brochure.
What does emergency power cost – and when is it worthwhile?
Specific amounts depend on the system; the structure is clear: the function costs a noticeable surcharge for the battery (switching device, additional wiring, planning), and it needs to be planned from the beginning – retrofitting an existing system is complex to uneconomical. Anyone buying the battery anyway and even considering emergency power should have both variants shown separately and decide with numbers.
And the honest classification regarding necessity: the Swiss electricity supply is one of the most reliable of all – outages are rare and usually short. Emergency power is therefore in the fewest cases a yield or risk calculation, but a question of priorities like the battery itself: anyone who relies on medical devices, works critically in a home office, lives remotely or simply wants the reassuring feeling, pays for a real equivalent value. Anyone who only fears the blackout from the headlines should first answer the sober question of how often their neighbourhood has been dark in the last ten years.
The desire for emergency power comes in waves in consultations – reliably whenever the topic of electricity shortages or blackouts has just gone through the media. We take the desire seriously, but first ask two questions: which devices should run – and for how long? The answers are revealing: «the whole house» almost always becomes «fridge, light, internet, mobile phone» in the conversation – and with that the necessary solution often shrinks from the expensive full switchover to a solid emergency power socket or a cleverly chosen backup power circuit. The counter-example also exists: households with a care bed or home dialysis, where we proactively advise automatic switching with recharge capability. Both decisions are correct – because they are thought of from the perspective of the devices, not the headline.
Frequently asked questions
Does my heat pump run on the battery during a power outage?
Generally no – starting currents and the continuous output of a heat pump overwhelm typical home battery emergency power solutions. With a correspondingly generous design it is feasible, but a special case. More realistically: keeping the control and circulation pump of an existing heating system in the emergency programme so that the house stays warm.
How long does a 10 kWh battery last in emergency mode?
That depends almost entirely on the consumers: fridge, light and router together use little – so a battery charge lasts a long time. Every large consumer drastically shortens the time. Systems that recharge with solar in island mode extend the supply in daylight practically indefinitely.
Does the system switch over automatically or do I have to do something?
Depending on the expansion stage: backup power systems switch over automatically within seconds; simple emergency power sockets sometimes require manual switching or plugging in. Clarify this before buying – in an outage at 11 pm the difference makes the comfort.
Can I retrofit emergency power to my existing battery?
Rarely sensible – the function is in the inverter, switching device and wiring, not just in the battery. Often it would amount to a system replacement. Anyone who ever wants emergency power plans it when buying the battery; the «maybe later» is more expensive here than with most other accessories.
Does an emergency power solution require a permit?
The installation is the responsibility of the electrical specialist company and is properly declared as part of the system notification to the grid operator – island mode capability needs to be professionally planned and documented. For you this means in practice: no visit to the authorities yourself, but a topic for the specialist company instead of an online purchase.
Free initial consultation
Emergency power – planned around the devices.
We clarify with you what should really run during an outage and quote the appropriate stage: socket, backup power circuit or real island system. With separately shown costs.
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Swissolar-certified specialist company · ESTI installation authorisation (Art. 14 NIV) · in Zurich since 2017 · over 150 systems completed · a personal answer from the specialist company, no call centre
Sources: Manufacturer documentation (emergency power/backup power system concepts); EnergieSchweiz (home battery basics); empirical values from the planning and installation practice of ecoEn GmbH, Zurich region.
Last updated: 9 July 2026 · Author: ecoEn editorial team
