Accelerating Solar Adoption Through Plug-in PVInsights from Germany’s Rapid PV Growth (2023/2024)

in Japanese

In 2023 and 2024, Germany saw a remarkable surge in PV installations, with around 16 GW of new capacity added each year—well above the national targets of 9 GW for 2023 and 13 GW for 2024 set under the Renewable Energy Sources Act (EEG 2023)¹. This puts the country firmly on track to reach its 2030 target of 215 GW of installed PV capacity.

Figure 1 illustrates the growth path required to meet the EEG goals of 215 GW by 2030 and 400 GW by 2040, highlighting the sharp uptick in past installations after 2022. Notably, actual installations in both 2023 and 2024 (yellow bars) exceeded annual targets (orange bars).

Although not shown in the figure, it's worth noting that roughly two-thirds of the newly installed capacity - about 10 GW per year - came from rooftop systems.

Figure 1: Past net growth until 2024 and paths to reach goals (EEG2023)

1. Drivers Behind Germany’s PV Boom in 2023/2024

Three main factors drove the sharp increase in solar - especially rooftop - installations in 2023 and 2024:

1. The 2022 Russian invasion of Ukraine heightened awareness of the need for energy independence and exposed the vulnerabilities of centralized grids, making decentralized rooftop PV both financially attractive and strategically essential.
2. Germany rolled out major policy improvement, leading to reduced costs, simplified permitting, and reduced bureaucracy.
3. Technological progress continued to lower PV costs and boost efficiency. Battery storage became more affordable and widespread, making rooftop PV even more appealing through improved self-consumption options.

Several key laws and policies that that significantly drove Germany's accelerated PV growth, are listed in the following:

• ・The Easter Package (“Osterpaket”, 2022)³, Renewable Energy Acceleration Package (“Beschleunigungspaket Erneuerbare Energien”, late 2022–2023)⁴ and related Amendments to the Renewable Energy Sources Act (“Erneuerbare-Energien-Gesetz – EEG”, 2022/2023) ¹ 
•  Increased Germany’s PV expansion targets significantly, aiming for 80% renewables by 2030, and classified renewable energy as being in the national public interest. Improved grid access and removed planning and permitting barriers; increased feed-in tariffs and subsidies; and expanded tender volumes for utility-scale systems—thereby accelerating PV deployment across all scales.
• ・Solar Package I (“Solarpaket 1”, 2023/2024)⁵
• Made plug-in PV easily accessible for everyone (see section 2-2). Reduced bureaucratic obstacles for smaller rooftop systems of <30 kW, enabling easier grid connection, registration and approval processes (e.g. PV operators can now replace older, less efficient modules with newer ones without losing existing feed-in tariff entitlements). Removed the mandatory direct marketing requirement for systems up to 200 kWp, allowing operators of such systems to feed surplus electricity into the grid without payment⁶. Eliminated power plant certification for systems under 500 kW and introduced dedicated auction segments for agri-, floating, and parking lot PV with higher bid limits.
• ・Building Energy Act (“Gebäudeenergiegesetz – GEG”, 2020) and related updates 2023⁷
• The GEG regulates energy efficiency standards for buildings in Germany, setting minimum requirements for insulation, heating systems, and the use of renewable energy in new buildings and major renovations. While it does not mandate PV systems at the federal level, it allows electricity generated from PV to count toward the renewable energy quota that new buildings must meet. This makes PV a cost-effective compliance option. In practice, the GEG contributed to a PV-friendly regulatory environment—especially when combined with emerging state-level solar mandates (“Solardachpflicht”) that require rooftop PV on new buildings in several German states.
• ・Tax Relief Measures (partly incorporated in policies mentioned above) since 2023   
• Exempted small to medium-sized PV installations (typically under 30 kW) from VAT (“Mehrwertsteuerbefreiung”), effectively making plug-in and rooftop PV about 19% cheaper immediately upon purchase. Additionally, income from electricity sales became tax-free for small systems, boosting financial attractiveness for households and small businesses.

2. Focus Plug-In PV: Decentralized Solar for Everyone

2-1 What are “plug-in PV” systems and what makes them different from regular PV?

Germany has seen a rapid rise in plug-in PV systems—commonly also known as mini-PV or balcony PV. These compact, plug-and-play units allow even tenants (not only homeowners) to produce their own electricity by mounting small solar panels on balconies, terraces, or similar structures (see Figures 2, 3).

Figure 2: Picture of a typical “balcony” plug-in PV 

Figure 3: Standard installation locations for plug-in PV

A plug-in PV system typically has a capacity of only 400 to 800 W. This does not seem much, but for many households, 800 W can easily cover daytime electricity usage, therefore reducing energy costs and increasing energy independence.

What sets plug-in PV apart is its simplicity: the system plugs directly into a standard German household outlet (“Schuko” plug, type F), with no special wiring or connection required. An integrated micro-inverter—usually attached to the back of the panel—converts DC to AC and is roughly the size of a paperback book. Once plugged in, solar power flows into the household circuit and can be used from usual household sockets. Any surplus electricity is generally fed into the grid without compensation. While selling excess power is technically possible, it’s rarely done, as it requires additional registration, a certified meter, and yields little financial benefit due to the small scale.

One common concern is the absence of outdoor outlets in some residences. To address this, the market has introduced innovative solutions, such as ultra-flat adapter cables designed for window and door passthroughs⁹. These cables are approximately only about 1.2 mm thick and can be clamped within the frame of a closed window or door, allowing the solar-generated electricity to enter the interior of the living space without any drilling or structural modification. This innovation has significantly broadened the accessibility of plug-in PV systems, especially for renters and those in buildings where installing external electricity outlets is impractical.

According to the German Environment Agency (UBA)¹⁰, the payback time for a typical 800 W plug-in system is under five years. This estimate assumes a €400 panel cost, vertical south-facing installation at a 90° angle (common but suboptimal), and electricity prices of €0.37 per kWh. Payback time shortens with lower panel costs, higher electricity rates, or better installation angles.

2-2 Plug-in PV development in Germany

Figure 4: Installed plug-in PV in Germany 2020-2025

As of April 21, 2025, Germany’s federal market master data register (MaStR)¹¹ lists 940,898 registered plug-in PV systems, of which 897,326 are operational (“In Betrieb”). Together, they represent a total installed capacity of 849.9 MWp (819.1 MWp operational). While this accounts for just below 1% of Germany’s total PV capacity, around 2.5% of new PV installations in 2024 (0.4 GW) were plug-in PV. It should also be noted that it is estimated that a large number of plug-in PV is not registered at the MaStR and therefore not mentioned in these statistics. It is hard to say how many unregistered plug-in systems exist. Based on an early study in 2022 by the HTW Berlin University of Applied Science¹² and recent market developments, the HTW Berlin Forschungsgruppe Solarspeichersysteme (research focus group solar batteries) estimate at the beginning of 2025 that the total number of plug-in PV (registered plus unregistered) is somewhere between 1.5 million to 4 million (1 - 2.6 GW installed capacity) ¹³.

Policy changes have played a key role in the plug-in PV development and its drastic increase in installation capacity. Until 2024, plug-in PV systems were limited to 600 W output. With the Solar Package I in 2024, the limit was raised to 800 W—while systems with up to 2,000 Wp of panel capacity remain permissible, provided the inverter output stays within the 800 W threshold.

The Solar Package I also simplified installation and registration. Self-installation is now permitted without the presence of a technician or grid operator. Landlords can no longer deny tenants the right to install a system without a valid reason, such as heritage building restrictions. Registration via the MaStR has been reduced to a short online form, making the process quick and accessible. Plug-in PV kits are readily available at hardware stores, allowing same-day purchase, registration, and installation. As with other PV systems, plug-in PV has been exempt from VAT since early 2024, reducing upfront costs by 19%.

2-3 How about technical and grid overload concerns?

As mentioned, plug-in PV systems connect directly into the home electrical circuits via standard wall sockets. Because of their simplicity, these installations raise several safety and technical considerations, especially related to electrical overload risks and grid integration.

One central issue arises from how plug-in PV systems integrate into a home's wiring. Typically, home electrical circuits are safeguarded by breakers designed to cut power if current exceeds safe limits, often around 16 A. However, plug-in PV inverters can feed electricity into household wiring downstream of these breakers, meaning the breaker only detects electricity drawn from the grid, not from the PV system. Consequently, the actual electrical load in the wires can be higher than the breaker detects. For example, if appliances draw around 16 A from the grid while simultaneously the plug-in PV inverter supplies another 3.5 A (approximately 800 W), the total current flowing through the local wiring reaches roughly 19.5 A - above the intended limit. Although rare, such undetected overload scenarios could gradually heat the wires, posing fire hazards, particularly in older buildings with outdated wiring.

Figure 5: Schematic of a home grid with plug-in PV

To address these concerns, German authorities originally set a cautious upper limit for plug-in PV systems at 600 W (approximately 2.6 A at standard household voltage in Germany). This conservative approach ensured that typical household wiring - usually rated to handle around 16 A - would comfortably absorb the additional current without significant safety risks. In 2024, Germany aligned its standards with European Union guidelines by increasing the permitted maximum size for plug-in PV systems to 800 W (around 3.5 A). Although this increment slightly increases the theoretical overload potential, it remains considered safe under normal operating conditions.

Features and safety recommendations¹⁴

As a precaution, German guidelines recommend additional safety measures for older homes or those with uncertain wiring quality. One practical solution is to install a dedicated electrical circuit for the PV unit, keeping solar-generated electricity separate from circuits that supply heavy appliances. It is also essential for homeowners to avoid connecting multiple PV inverters to the same circuit or using extension cables, both practices significantly raising the risk of overload.

Germany mandates that plug-in PV inverters must meet rigorous electrical safety regulations, specifically the VDE-AR-N 4105 standard. Among the requirements is an essential protective function called anti-islanding (known in Germany as "NA-Schutz"), which ensures the inverter instantly shuts down during power outages. This prevents electricity from unintentionally flowing into the external grid, safeguarding line maintenance workers and infrastructure. Moreover, these inverters contain internal safeguards such as thermal protection and maximum current limits, further enhancing their safety under normal operating conditions.

Finally, metering and grid compatibility are important concerns for plug-in PV systems. While modern digital electricity meters easily handle two-way energy flows, older mechanical meters (Ferraris meters) were not originally designed for this purpose. When excess solar electricity flows into the grid, these older meters may spin backward, reducing the recorded amount of electricity purchased from the grid, which was previously seen as legally problematic. To resolve this, utility providers typically replace older meters with new digital models containing built-in backflow protection ("Rücklaufsperre"). Interestingly, Germany introduced a temporary policy adjustment in 2024 allowing a brief period during which newly installed plug-in PV systems are allowed to use backward-running mechanical meters until a new digital meter is installed.

2-4 Impact of plug-in PV

Beyond their contribution to electricity generation, plug-in PV systems have played a key role in broadening public engagement in the energy transition. They have made solar power accessible to apartment dwellers who previously had no way to participate in green energy generation. At the same time, plug-in PV has helped raise awareness of the potential of solar energy more broadly. Many people - particularly in rural areas - who first experimented with plug-in PV have since upgraded to full rooftop systems after seeing the benefits firsthand. This trend is expected to continue, further supporting Germany’s climate and energy goals.