Plug-in Solar SystemsGlobal Expansion and the Status in Japan

in Japanese

1.　Introduction

In our previous column “Accelerating Solar Adoption Through Plug-in PV”, we explored the growing popularity of plug-in solar systems, compact photovoltaic units that can be installed on balconies or other places and connected directly to a standard household socket, in Germany.

Plug-in PV is not just a technical innovation. It represents a shift in how energy is produced and who gets to participate. Until now, installing solar panels at home was a privilege limited to detached homeowners. Plug-in PV systems, however, allow residents of rental housing and multi-family dwellings—those without rooftop rights—to generate their own solar power without complicated procedures. As such, they are gaining attention as a new means for wider citizen participation in the energy transition.

This follow-up expands the focus beyond Germany and explores the potential for plug-in PV in Japan. By looking at the regulatory frameworks and operational practices in different countries, we aim to clarify the institutional and technical challenges Japan faces. Ultimately, we explore directions for regulatory reform to make plug-in PV a realistic, safe, and legal option for Japanese households.

2.　Plug-in PV Around the World

The growing importance of plug-in PV can be seen in the fact that the world’s first “Plug-in solar conference” was held on May 8th 2025 in Munich, Germany¹. In their Joint Declaration², the conference members declared (among other points) that “Citizen participation is essential” in achieving 100% renewable energy systems globally, and that plug-in technologies drive participation in the renewable transition. “The future is in the hands of citizens… by empowering individuals, families, and communities, we can ensure a faster, fairer, and more resilient energy transition.”

While plug-in solar systems are most visible in Germany, interest in this technology is spreading globally as cities search for low-cost, citizen-led solutions to accelerate decarbonization. Plug-in PV are small-scale photovoltaic systems — typically below 2000 W_DC installed capacity — that are designed for self-consumption, easy installation (often by the user), and direct connection to household electricity systems without requiring large construction or full professional electrical setup. These systems generally include one or two panels and a micro-inverter, often limited to 800W_AC, and are particularly well-suited for balconies or small outdoor areas in urban environments. This chapter looks at the legal situation of plug-in PV in selected countries around the world.

2.1 The European Union

The EU encourages its member states to promote the adoption of plug-in PV. In particular, the “EU Directive on improving the Union’s Electricity Market Design”³ calls for the establishment of simple and non-discriminatory systems to ensure that all citizens can access such technologies.

On the other hand, when it comes to the technical requirements for plug-in PV, there are currently no unified regulations that apply across the entire EU. The EU has established common requirements only for generation systems with an output of 800 W_AC or more⁴.

Currently, 25 out of the 27 countries in the EU have legalized plug-in PV⁵. The only two countries where plug-in PV is not legal are Sweden and Hungary. It should be noted that specific installation data is limited since few countries have a separate registry for plug-in PV, and even those that do have a registry (like Germany) have a high number of unregistered installations.

The growth of plug-in PV internationally depends heavily on national regulations concerning electrical safety, feed-in arrangements, grid connection, and tenant rights. Below, we outline some key developments in selected countries. Another wider overview over various EU member states can be found in “Plug-in Solar PV” report by SolarPowerEurope⁵, which was published in March 2025.

■Germany
Germany is currently the global frontrunner in plug-in PV. Systems under 800 W_AC (2,000 W_DC) can be installed without grid operator approval, provided the system is registered with the Federal Network Agency (MaStR, simple online registration). Reverse current into the grid is allowed, though usually not remunerated. The plug-in PV system, particularly the microinverter, needs to be CE-certified (“Conformité Européenne", EU conformity marking to meet safety, health and environmental protection requirements)⁶ and conform with safety regulations, such as anti-islanding protection. Legal reforms, particularly in 2024, have also strengthened tenant rights to install solar systems, even in apartment buildings. The result: over 1,000,000 systems registered as of July 2025⁷, with steady growth. Please check the details in our previous publication.

■Austria
Austria follows a similar model to Germany. Plug-in systems up to 800 W_AC are allowed and considered “electrical appliances” if safety standards (such as anti-islanding protection) are met and the system has the CE marking⁸. The registration is simplified (often online). Starting September 1, 2024, owners in apartment buildings can install plug-in solar systems without unanimous approval by other co-owners - consent is assumed if no one objects within two months, and objections must be well justified. Unfortunately, this legal simplification does not apply to tenants, who still must seek permission. If not otherwise required by the local grid operator, self-installation is allowed. Reverse current into the grid is allowed but not remunerated⁹. To encourage the installation of plug-in PV (and PV in general), since January 2024 PV systems below 35 kW_DC capacity are exempt from VAT, similar to Germany¹⁰. According to SolarPower Europe, the annual market for plug-in PV systems in 2023 and 2024 was in the 10-15 MW range, with an increasing number of registrations⁵.

■Belgium
Belgium just recently permitted up to 800W_AC plug-in PV in late March 2025. To allow the installation of plug-in PV, Belgium policy makers had to change how electricity generating devices should be connected to the grid¹¹. With the new regulatory classification, plug-in devices are now treated as “products” and not full electrical installations. Before the changing of the rule, such electrical installations were subject to conformity checks before commissioning and on-site inspections, therefore not suitable for plug-in applications. However now, no prior inspection or site verification is required before usage of plug-in PV (unlike with fixed PV systems). Despite that, safety responsibility remains, and the user must ensure compatibility and safety of the connected electrical system. Also, the devices must have CE marking, a Declaration of Conformity, and meet general electrical safety standards. It is also recommended that the devices are plugged into a separate circuit. The unit needs to be registered by the local grid operator¹².

■France
France permits plug-in PV of less than 3 kW_DC (600 W_AC)⁵. For ground-mounted systems no registration is required when they have a capacity and the total height of the installation is less than 1.8m (exception are protected building zones)¹³. However, if the system is attached to the exterior of a building, such as the balcony or façade, registration is required at the French municipality, and the permission of the landlord needs to be obtained since it alters the appearance of the building¹⁴. Installation by a professional is not a requirement unless the system is feeding into the grid⁵. French and European safety norms for each component need to be met. The “PVPS National Survey Report of PV Power Applications in France 2023”¹⁵ report suggests a growing number of installations in its text and the “Plug-in Solar PV” report published by SolarPower Europe⁵ mentions that ENEDIS (French DSO) tracked 34 MW of installed PV systems that are smaller than 1 KW by the end of 2024.

■Sweden
Sweden is one of only two countries in the EU that currently prohibits plug-in PV systems due to safety concerns. All grid-connected solar installations must be professionally wired and approved. The Swedish National Electrical Safety Board (Elsäkerhetsverket) writes in 2022 that connecting an electricity-producing unit via a standard household socket violates the current Swedish standard¹⁶. It mentions that one of the biggest concerns is that the unit can feed power behind standard fuses, risking overloading or fire, and the breaker may not trip (we talked about this concern in our previous column as well). According to the document, Swedish standards only permit power generators that are permanently connected (therefore not plug-in) and safely matched to the system.

2.2 Other parts of the world

■United States
Plug-in PV is not yet widely supported by regulation in the US, but in March 2025 the state of Utah made plug-in PV legal. By a new law ¹⁷, portable solar devices are not required to sign an interconnection agreement with their local grid operator anymore. Plug-in systems of less than 1200W_AC can now be directly plugged into a wall socket. As a requirement, the PV system needs to meet the UL (Underwriters Laboratories) and NEC (National Electrical Code) certifications. According to PV magazine, at this point no such system exists in the US¹⁸. Nevertheless, the new legislative measure is an important step to spread plug-in PV in the future.

■Australia
Australia has strong solar uptake but limited legal support for plug-in systems. The biggest hurdle is an Australian standard that requires all grid-connected inverters to be hard-wired to a dedicated circuit in the switchboard, not plugged into a standard power outlet^19, 20. This effectively makes plug-in PV illegal in the country. Additionally, plug-in PV does not seem to be a discussion topic, maybe because of Australia’s large area, and the fact that only a small percentage of dwellings in Australia are apartments (16% apartments, 13% townhouses, 70% separate houses)²¹, potentially making rooftop solar a more prominent choice. According to Australia’s Clean Energy Counsil “Rooftop solar and storage biannual report” published in March 2025, rooftop PV installations surpassed four million installations at a cumulative total capacity of 25.5 GW in 2024, which contributed to 12.4% of Australia’s total energy supply in that year²².

2.3 Summary of the situation around the world

The examples given in the previous section show that plug-in PV is becoming increasingly common. Looking at Germany, Belgium and the US, it is obvious that laws and regulation concerning plug-in PV are evolving to be more inclusive. It should also be mentioned that of course safety concerns are valid and should be addressed. It is important to use certified products and follow installation guidelines. Guidelines and regulations are necessary to provide a safe and secure energy transition, particularly for self-installed plug-in PV devices. Germany and Austria stand out as leaders due to clear regulatory and simplified connection procedures, and according to Austria’s official consumer information organization, neither the Austrian side nor their German counterpart (Deutsche Verbraucherzentrale) is aware of any case in which a plug-in solar device has caused property damage or personal injury⁹.

3.　Current Situation and Barriers in Japan

In Japan, solar power systems under 10 kW_AC are classified as general electric installations and in contrast to EU regulations, there is no defined lower limit (such as 800 W_AC). This means that such systems, even if intended primarily for self-consumption, are subject to the same regulations and technical requirements as, for example, general rooftop PV systems of 10 kW_AC. In short, plug-in PV systems designed to connect directly to household outlets are not envisioned under Japan’s current regulatory framework. We will look at some of the requirements under the current regulations below.

・Technical Requirements
To connect a solar PV system to the grid, two technical standards must be met:

In particular,

•    If reverse power flow is present, an anti-islanding protection device must be installed to ensure safety during power outages.
•    In cases without reverse power flow (self-consumption only), the installation of an anti-islanding device is not required. However, to ensure safety and comply with contractual conditions, the installation of a reverse power relay (RPR) that shuts down the inverter in the event of reverse power flow is required.

To illustrate this point, the wiring system configurations in Germany and Japan are compared in Figure 1. In Germany, reverse power flow is permitted, and safety functions, such as anti-islanding, are integrated into the inverter. Plug-in PV systems can be used simply by connecting them to a standard electrical socket. In contrast, under current regulations, Japan requires dedicated wiring and simple plugging-in is not allowed. Anti-islanding and safety functions could technically be included in the inverter, but an RPR would need to be installed separately in the case of self-consumption only (no reverse power flow). 

Figure 1. Conceptual Diagram of Current PV Wiring

・Usage of a licensed electrician
Article 3, Paragraph 2 of the Electrician Law²⁶ stipulates that only individuals holding a First-Class or Second-Class Electrician license may engage in work related to general-use electrical installations. Accordingly, electrical wiring work for solar power systems classified as general-use electrical installations, such as systems under 10 kW_AC (including those around 800 W_AC), must be carried out by a licensed electrician, even if the work is performed inside a household.

・Application to the grid operator
Application to the local grid operator is necessary. For solar PV systems under 10 kW_AC connecting to the grid at low voltage, the application procedures and required forms are provided on each regional transmission and distribution company’s website²⁷. These procedures must be followed. Technical requirements differ between cases with reverse power flow and without reverse power flow. Also, the PV system and its components must be certified by a third-party institution, or individual conformity assessment is required.

4.　To promote adoption in Japan

Despite growing international recognition of plug-in PV as a tool to accelerate citizen participation in the energy transition, Japan’s current regulatory framework does not accommodate such systems. Even small-scale units below 800 W_AC, commonly designed for self-consumption, are subject to the same rules and regulations as much larger rooftop systems. As a result, plug-in PV remains inaccessible to residents, especially in urban areas where apartment living is the norm.

To unlock the potential of plug-in PV in Japan, a clear shift in regulatory and institutional thinking is needed. Three priority areas stand out:

1. Legal Recognition and Definition
Japan should introduce a distinct legal category for power generating systems under a certain threshold (e.g. 800 W_AC), which would distinguish plug-in PV from larger, conventional PV systems. This would allow for proportional technical standards and simplified administrative requirements in line with international trends.

2. Simplified Technical and Procedural Standards
New technical guidelines should allow for:

• Self-installation (plug-in connection), without dedicated wiring
• Standards for certified micro-inverters used in PV with built-in safety features, such as disconnecting the device in case of power-failure or accidental unplugging

Furthermore, grid connection procedures should be streamlined – ideally allowing for automatic approval upon online registration (as in Germany’s MaStR).

3. Designing Future Buildings for Plug-in Readiness
In parallel to technical regulations, consideration could be given to updating building standards to require plug-in PV–ready designs in new multi-unit housing—for example, by promoting the installation of outdoor electrical sockets on balconies to facilitate future adoption.

In addition to regulatory reforms, Japan should support targeted demonstration projects, focusing on collective housing and rental properties, where plug-in PV offers the greatest untapped potential. Existing initiatives - such as NEDO’s Demonstration Project for Multi-Purpose Applications of Solar Power²⁸, which included research and development on balcony-mounted systems, or the Solar Power Development Strategy 2025²⁹ - can provide a foundation. International experience, particularly from Europe, should be leveraged to adapt global best practices to Japan’s unique technical and legal context.