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Glossary · Energy industry & energy transition

Balcony power plant, plug-in solar device

Balcony solar system plug-in solar device photovoltaics prosumer Self-Consumption low voltage electricity consumption

A balcony power plant is a small photovoltaic system for self-consumption. It is usually connected to the electrical circuit of an apartment or house via a socket or a special energy plug connector. In German law it is called a Steckersolargerät (plug-in solar device). The Renewable Energy Sources Act (EEG) defines it in § 3 No. 43 as a device consisting of one or more solar installations, an inverter, a connection cable and a plug for connection to the final circuit of an end consumer. The electricity generated is first used by the appliances running at the same time in the same household. Only when generation exceeds instantaneous consumption does the surplus flow into the public low-voltage grid.

Design and key parameters

Two power figures are important for a plug-in solar device. The module capacity is stated in watt peak (Wp). It describes the direct-current output of the solar modules under standardised test conditions, that is, a laboratory value. How much electricity the modules actually deliver depends on orientation, tilt, shading, temperature and season. The inverter converts the direct current into grid-standard alternating current. Its output power is stated in volt-amperes (VA) or watts and determines the maximum power that can flow into the household network. If the modules are more powerful than the inverter, part of the possible output is clipped on sunny middays. In return, the system delivers more in the morning, in the evening and under cloudy skies.

A balcony power plant generates electrical energy, measured in kilowatt-hours. This must be distinguished from power: it describes how much electricity flows at a given moment. A module can deliver high power on a sunny midday, but at night it delivers nothing. For the electricity bill, what counts is the number of kilowatt-hours consumed by the household itself over the year. For the power grid, it is also important when electricity is fed in and how the feed-in overlaps with local consumption.

Legal framework in Germany (as of November 2026)

Since the entry into force of Solar Package I on 16 May 2024, special rules for plug-in solar devices have applied in the EEG. They concern only devices first put into operation from that date. The requirements are:

  • Capacity limits: The installed module capacity is at most 2,000 watts, and the total inverter capacity is at most 800 VA. All plug-in solar devices behind the same withdrawal point are added together, that is, behind the meter through which the household draws electricity. Two devices of 600 VA each therefore no longer fall together under the special rules.

  • The highest adjustable value is decisive: If an inverter can be set to 900 VA, the special rules do not apply even if it is throttled to 600 VA in operation.

  • No remuneration: The device must be assigned to "unremunerated acceptance" (unentgeltliche Abnahme). The grid operator accepts the surplus electricity, accounts for it and markets it, but pays no feed-in tariff for it. Anyone who instead claims the regular EEG remuneration cannot use the simplifying special rules.

  • Registration: The device is registered exclusively in the Marktstammdatenregister (core energy market data register) of the Federal Network Agency (Bundesnetzagentur). A few details are sufficient for this. Within the capacity limits, a separate registration with the grid operator is no longer necessary.

For plug-in solar devices too, an unsuitable meter must be replaced. Under § 10a EEG, the grid operator equips the metering point with a modern metering device as a bidirectional meter or with a smart metering system. Until then, the device may already be operated. An old Ferraris meter that runs backwards when electricity is fed in is tolerated on a transitional basis. The earlier statement that modern meters would prevent backward running from the outset therefore applies only after the replacement. According to the Federal Environment Agency (Umweltbundesamt), the operator incurs no additional costs from the replacement and operation of the new meter compared with the previous meter.

Since December 2025, DIN VDE V 0126-95 has provided a dedicated product standard for plug-in solar devices as a complete system. It sets out safety requirements and tests and, under certain protective measures, also permits connection via an ordinary Schuko plug to a household socket. The installation standards for house wiring apply in addition. With Solar Package I and changes to tenancy and condominium law, operation was also made easier in 2024 for tenants and condominium owners. Installation must nevertheless be safe, and requirements on fastening, design and building safety remain in place.

Distinction from rooftop systems, storage and emergency power supply

A rooftop system is usually permanently installed, considerably larger and connected by a licensed electrical contractor. A plug-in solar device, by contrast, is designed for small capacities, simplified registration and low technical complexity. It is not storage: without an additional battery storage system, it cannot save electricity for later. Nor is it an emergency power system. If the grid fails, the inverter switches off so that no electricity flows into a de-energised grid on which work may be under way. This shutdown is a safety function and not a defect.

When a balcony power plant pays off

The benefit arises when generation and consumption take place at the same time. If a refrigerator, router, computer, washing machine or heat pump runs during the day, part of this consumption can be covered directly by the solar modules. As a result, the household has to draw less electricity from the public grid. Since the surplus goes into the grid without remuneration, the economic value lies almost entirely in the electricity purchase saved. How high it is depends on how well the generation profile matches the household's load profile.

Annual generation is often compared with a household's total electricity consumption. This gives only a rough impression. A household with an annual consumption of 3,000 kilowatt-hours does not automatically use everything the device generates in a year. Anyone who uses hardly any electricity during the day achieves a lower self-consumption share than a household with continuously running appliances or loads that can be shifted to the midday hours.

A self-consumed kilowatt-hour replaces electricity at the household electricity price. Besides energy costs, this price includes network charges, taxes, levies and distribution costs. For the household, it is therefore usually worth more than a kilowatt-hour fed in. From the point of view of the power system, however, the household remains dependent on the grid whenever the sun is not shining or the output is insufficient. A balcony power plant reduces the quantity of electricity drawn, but replaces neither the grid connection nor any appreciable secured grid capacity.

Role in the power system

The name "power plant" can be misleading. Feed-in follows the supply of sunlight and can hardly be planned without storage or control. A plug-in solar device provides no firm capacity, does not contribute to frequency maintenance and cannot actively compensate for disturbances in the local grid. Its purpose is to generate small quantities of electricity in a decentralised way and to reduce one's own grid consumption. Many devices together can become relevant in aggregate, but remain dependent on weather and time of day.

For the low-voltage grid, a single system is usually unproblematic. Many systems in one street, however, can change power flows on sunny days: instead of flowing almost exclusively from the local distribution transformer to the households, net consumption falls, or electricity temporarily flows back. Registration in the Marktstammdatenregister therefore creates transparency about the growing number of small feed-in units in the distribution grid. The data are forwarded automatically to the responsible grid operator.

Anyone who operates a balcony power plant generates and consumes electricity and thus becomes a small prosumer. An active role in the electricity market does not follow from this. Most devices respond neither to prices nor to grid signals. They generate electricity as soon as light falls on the modules. Only in combination with controllable loads, storage, dynamic tariffs or energy management systems does genuine flexibility arise.

Assessment

Balcony power plants make participation in the energy transition easier, especially for people without their own roof. However, they raise false expectations if they are presented as a substitute for grid expansion, large generation plants, storage or flexible demand. Strictly speaking, the term denotes neither an autonomous electricity supply nor a full-fledged power plant. It refers to a small, grid-connected photovoltaic device for direct self-consumption. Its effect depends on solar power and household consumption coinciding in time, on its being connected safely, and on many small feed-in units becoming widespread.

Sources

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Edited by eCMS on 11.11.2026 15:08

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