Introduction
Imagine living in an apartment in Berlin with two solar panels installed on your balcony. You plug them in, and your washing machine, dryer, and electric fan start running one after another, while the electricity meter stands still—this isn't a scene from a science fiction movie, but a real scenario in Europe's current energy transition. According to the latest "Plug-In Solar PV" report by SolarPower Europe, a technology known as "plug-in photovoltaic systems" is sweeping across the European continent, with Germany at its epicenter. It allows renters and low-income households to enjoy green photovoltaic power and save on their electric bills. Furthermore, VDE is set to release the world's first technical standard for plug-in PV systems in the third quarter of 2025. According to the latest information, this standard will cap the system's installed capacity at 960W.
Figure: SolarPower Europe
As the "Silicon Valley" of plug-in systems, the German market is experiencing explosive growth:
Annual registered number of plug-in PV systems in Germany (Figure: SolarPower Europe)
Other countries exhibit three development models:
EU Policy Framework: The 2024 Electricity Market Design Directive (EU/2024/1711) gives a "green light" to small-scale systems, recommending that member states exempt them from approval processes and allow grid feed-in. However, the specific rules are still left to each country to decide. This model of "unified principles, divergent implementation" has become the root cause of market fragmentation.
Figure: SolarPower Europe
The "hidden feature" of plug-in systems is that the capacity of the DC side (photovoltaic panels) can be higher than the limit of the AC side (inverter). For example, one could install 2kW of PV panels (DC side) with an inverter that limits the current to 800W (AC side). This design can compensate for efficiency losses due to shading or non-ideal angles, thereby increasing power generation. With the growing adoption of energy storage systems, DC oversizing is becoming increasingly common; the largest systems have reached configurations of an 800W inverter paired with 6kW of PV modules and a 25kWh energy storage system.
| Country | DC Side Limit | AC Side Limit | Oversizing Margin |
|---|---|---|---|
| Germany | 2kW | 800W | 150% |
| France | 3kW | 600W | 400% |
| Switzerland | 600W | 800W | -25% |
| Austria and other countries | Unlimited | 800W | Free oversizing |
Key Conflict: The greater the oversizing capability, the higher the system's cost-effectiveness. However, it may pose risks such as cable overheating and grid fluctuations; in severe cases, it can cause fires (Reference article: Is Lithium Iron Phosphate No Longer Safe? A German Residential Energy Storage Fire Sparks 5 Conjectures). Germany's approach is a case in point: the VDE standard requires dynamic current limiting through software in the Power Conversion System (PCS) to ensure the AC side output does not exceed 800W. Spain, on the other hand, effectively kills the economic viability of oversizing by mandating the installation of a separate circuit (requiring an electrician).
Annual installation volume of small-scale energy storage systems (<5kWh) in Germany (Source: SolarPower Europe)
In countries that use Schuko (e.g., Germany, France), users can perform DIY installations, and the market size has grown by over 200% annually. In countries that mandate Wieland (e.g., Spain, Sweden), system costs increase by 30%-50%, relegating them to a niche market.
Figure: SolarPower Europe
The VDE 0126 95 standard, developed by the German Association for Electrical, Electronic & Information Technologies (VDE), is the first comprehensive technical specification for plug-in systems. It covers:
The final version of this standard is scheduled for release in the third quarter of 2025. The Netherlands and Austria have already indicated they will reference the VDE standard. Although the standard is not mandatory, landlords and insurance companies are likely to use it as a benchmark, which could have a significant impact on the plug-in PV system market.
Plug-in PV is often referred to as "balcony solar" in the media. However, actual balcony installations currently account for less than one-third of all plug-in PV systems. More plug-in systems are installed in yards, patios, on rooftops, and on facades.
