In 2025, an important change came into effect in the regulation of domestic solar systems: from now on, the construction of grid-connected systems with backup/EPS (Emergency Power Supply) functions is officially permitted.
This is especially a step forward for the general public. Previously, household-scale solar power plants (HSPPs) would automatically shut down during a power outage. There was no way for our own solar system to provide energy during this time – regardless of whether the sun was shining or we had batteries.
The new regulation now changes this: with appropriate technical design, it is now possible for a solar system to operate even during a power outage - i.e. to switch the household to island operation.
In this article we will introduce:
- what types of systems exist (grid-fed, stand-alone, hybrid);
- what the backup/EPS function means from a technical and legal perspective;
- how the regulations have changed from 2025;
- and what to pay attention to during design and construction
We will also discuss the benefits this brings to households, and briefly discuss the impacts on industrial systems.
Types of solar systems – a brief overview
To understand the essence of the backup/EPS function, it is worth first reviewing how the different types of solar systems work. We distinguish three main types - based on their connection to the public grid:
Grid-tie system:
This is the most common type.
The solar panels and inverter are continuously connected to the utility grid. The generated energy is first used by the household, and the excess can be fed back into the grid, if permitted.
An important limitation: in the event of a power outage, such a system automatically shuts down. Since there is no grid reference voltage, the inverter stops working – and for safety reasons, it shouldn’t. The purpose of this is to prevent feedback into the grid while maintenance workers are working on it.
Off-grid system:
This type is completely independent of the public network.
The solar panels, inverter and battery together form a closed, self-contained system – from where all consumers in the household receive their electricity. A power outage does not affect such a system at all.
This solution is mainly typical in places where there is no available electrical network, or where the owner consciously strives for complete energy independence.
The disadvantage is that it requires a larger battery capacity to maintain continuous supply - especially during longer cloudy periods or winter months.
Hybrid system:
This solution is a combination of the two.
A hybrid system is connected to the grid, but also has a battery and is able to automatically switch to island operation in the event of a power outage - provided it also has a backup/EPS function.
Under normal circumstances, the system cooperates with the grid: it uses what it produces, feeds back the excess, and, if necessary, draws from the grid.
However, in the event of a power outage, it can continue to operate as an independent island, disconnecting itself from the grid - this is called backup or EPS operation.
Many people have been looking for this solution in recent years, but it has not been officially permitted in Hungary until now. However, this has now changed – and this is what the next part of the article is about.
What is the backup/EPS function and how does it work?
The backup – or EPS (Emergency Power Supply) – function is designed to ensure that the solar system is able to provide power even when there is no mains voltage. In Hungarian: if there is a power outage, the system does not stop completely, but continues to operate and provide energy to certain consumers – or even the entire household.
Of course, a battery is not enough for this. The system must be able to “disconnect” from the public grid and switch to stand-alone operation. This is ensured by a separate output – the so-called backup or EPS output – and an associated automatic control unit. As soon as the system detects that a power outage has occurred, the inverter switches to stand-alone operation and supplies energy only to the in-house grid. The connection to the external grid is interrupted, thus eliminating the risk of back-up power – which in such cases is not only irregular, but can also be life-threatening.
An important difference is that most conventional solar systems will shut down during a power outage, even if they have batteries. In this case, the inverter “does not know” what to do – because it does not have a built-in backup function and cannot disconnect from the grid. A true backup system, on the other hand, works like an uninterruptible power supply: it automatically switches over within a few milliseconds and the power supply continues uninterrupted. Most household devices – such as lighting or the internet – do not even notice this switch.
However, the system can only provide power as long as there is enough. If the sun is shining, the solar panels produce, but if it is cloudy or at night, the battery capacity sets the limit. Therefore, good sizing is key: you need to know how long and what devices you want to supply. A smaller storage unit may be enough for a shorter outage, but if the goal is to control the refrigerator, lighting and heating for hours, for example, then a larger capacity will be needed. Large consumers – such as the oven or washing machine – are usually not put on the backup branch in such cases, or only with conscious planning.
Why wasn't backup mode allowed in Hungary until now?
There were several reasons behind this, primarily security and legal ones, which prevented the spread of backup technology for a long time.
Contact protection and life safety
The most important concern was the risk of accidents caused by backfeed. If the public grid goes down, for example due to maintenance or a fault, no home power plant – not even a small solar system – can feed back energy. An unexpected backfeed would pose a direct threat to the lives of professionals working on the grid, who expect to be without power in the lines while working.
Therefore, it is strictly required that grid-connected inverters automatically stop when the grid disappears. International standards, such as the so-called “anti-islanding” protection, serve exactly this purpose: inverters must be able to detect a grid failure and immediately interrupt production.
The reconnection is also controlled
When the grid is restored, there is also no way to reconnect in any way. Service providers often require delayed reconnection – typically with a delay of 1–5 minutes – to prevent many separate solar systems from starting to feed back at the same time, which could lead to sudden voltage fluctuations. If a system operates in island mode but does not reconnect to the grid in a synchronized manner, it can cause serious frequency and voltage problems. To avoid these, hybrid or backup systems were previously excluded from being allowed.
Regulatory gaps and provider refusal:
Even if the technology was ready – several manufacturers, such as Fronius or Solax, had been offering inverters with backup outputs for years – the official regulations did not address this. It was unclear under what technical and legal conditions a system could be both grid-connected and stand-alone.
Therefore, service providers consistently refused to install such systems. The connection regulations clearly stated that solar systems with backup functions connected to the public grid were not permitted. Users who still insisted on power failure protection could only think of “workarounds” – for example, through separate socket outlets belonging to some inverters, such as the Fronius PV Point. However, these could only supply power to a few small devices (e.g. lamps, routers) and were not integrated into the entire house network – so they could not really be considered a real backup solution.
The 2025 rule change: what does it allow and what has changed?
One of the most important innovations is that Act LXXXVI of 2007 – more commonly known as the Electricity Act – officially introduced the concept of “household electricity storage”. According to this, any battery-powered device with a capacity of at least 2 kWh, which can be operated independently and is rechargeable, can now be recognized as part of the electricity system. This means that the role of home battery storage has become recognized – not only technically, but also legally.
The regulation also clarified the technical conditions for “mixed mode” (i.e. simultaneously connected to the grid and capable of stand-alone operation) systems. For example, the so-called Annex 6/B of the grid regulation describes in detail what additional requirements such a system must meet. This includes, for example, the presence of an automatic disconnecting device, the safe design of stand-alone operation, and the presence of the necessary protection functions.
In practice, this means that from 2025, service providers can accept household solar systems that can switch to stand-alone operation in the event of a power outage in addition to conventional operation. However, this is not an automatic option for all systems. Only those that fully comply with the relevant technical and safety regulations can be granted a permit with a backup function. During implementation, it is therefore not enough to simply install the hardware: the required standards, the design of appropriate protection, and consultation and approval with the service provider must also be taken into account.
This change is particularly important for the population, as it significantly increases security of supply. During a regional or national power outage, the house does not have to be plunged into complete darkness – if there is a battery and the system is prepared for backup operation, then at least the basic devices (such as refrigerator, lighting, heating control) can operate without interruption.
It is worth mentioning that the regulatory direction aims to encourage home energy storage and self-consumption. This is also reinforced by the fact that from 2024 gross settlement replaced the previous net model – meaning that the energy fed back is financially less worthwhile than the energy we use locally. The backup system combined with a battery is also an advantage in this situation: it helps to utilize our own production in-house and also acts as emergency protection.
Licensing and installation conditions in practice
Building a solar system with backup/EPS functionality is not only technically challenging, but also administratively. Many people are in a situation where they already have solar panels and possibly batteries, but would like to expand the system with a stand-alone solution. In such cases, a new notification must be made to the service provider, as if it were a new request.
The service provider typically requests the following:
- New application: it must be indicated that the system will also be capable of backup/power failure mode.
- Modified connection plan: must include the technical solution, EPS connection details, wiring diagram, equipment types.
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New completion report : after construction, it must be confirmed that everything was done according to the approved plan.
These steps are the same as when setting up a new HMKE, only now the documentation is expanded due to the backup function.
When designing a new system, it is worth indicating the need for backup from the beginning. This way, the designer works with inverters and accessories that are on the list of approved devices and comply with the relevant standards (e.g. EN 50549, anti-islanding certification, etc.).
It is important to involve an expert, because:
- Network protection settings (e.g. VDE AR-N 4105) require precision.
- The professional installation of the backup switch (e.g. EPS relay) is crucial.
- It may also be necessary to install a bidirectional meter.
The heart of the backup system is the automatic transfer unit, which disconnects the household from the utility grid in the event of a power outage. The system should operate in such a way that the entire house normally operates from the utility grid, but in the event of a power outage, it directs power supply either to a separate backup circuit (important consumers) or even to the entire house - but never feeds back into the grid.
Hybrid inverters and backup solutions
More and more manufacturers are offering hybrid inverters with backup functions, but it is important to make a distinction: not all hybrid inverters can automatically switch to stand-alone operation. This requires the appropriate function and often an additional device.
- Deye inverters: have a factory-integrated backup function. No separate EPS box is required, the inverter can handle a power outage on its own.
- SolaX and Huawei inverters: a separate additional module is required (EPS or Backup Box) that provides automatic transfer. These contain two magnetic contactors: one disconnects the grid, the other connects the internal network of the house to the inverter.
- Huawei Backup Box: available in single-phase and three-phase versions. Provides fast switching and can even supply an entire household.
- SolaX EPS Box: a separately available unit, without which the inverter cannot operate in stand-alone mode. Once installed, it forms a complete backup system.
The goal is always the same: to automatically and safely disconnect the household, then supply the internal consumers with power using the battery and solar panels. The switchover time is usually a few hundredths of a second – so no router or computer will necessarily restart.
What should you pay attention to when planning?
- Backup operation does not mean that all consumers can operate without restrictions.
- The inverter's power and battery capacity determine what can be operated during a power outage and for how long.
- It is worth connecting only the most important devices to a backup circuit: lighting, refrigerator, heating circulator, router, security technology.
- It is not advisable to use heavy consumers (oven, air conditioner, car charger) in backup mode - unless the system is designed for it.
Installation specialists will help you calculate the required battery capacity: this requires knowing the performance of the devices being backed up and the expected operating time. Based on this, you can determine the required kWh capacity – whether it is a few hours or a day of bridging.
Summary
A solar system with a battery does not in itself mean stand-alone operation capability – this requires the installation of a backup or EPS function. In Hungary, this has not been permitted by service providers and regulations until now, due to safety considerations. However, this has changed from 2025: hybrid (grid-connected, but also operational during power outages) solar systems have become officially permitted.
In practice, this means that a well-designed and implemented backup system can ensure that power outages can be bridged without having to give up the benefits of grid connectivity. For users, this means greater independence, security and more efficient energy use.
However, it is important that the implementation is professional. This is the only way to ensure that the system meets the relevant standards and service provider expectations. It is worth entrusting the work to an experienced design and construction team.
The winners of the regulatory change can therefore be all actors: the population, network operators, and even industrial consumers. Systems with backup functions make the country's energy system more stable and bring us closer to a sustainable, renewable-based future.
