In the German balcony photovoltaic product standard VDE V 0126-95:2025-12, the AC output power limit for balcony PV systems is set at 800 VA, and the DC installed capacity limit at 2 kWp. This is based primarily on research by Joseph Bergner of the Berlin University of Applied Sciences and Technology (HTW Berlin). This article briefly introduces that research, placing it in the context of the technology’s development history for readers’ reference.
1.Germany’s original balcony PV power limit was set at 600 W, referencing regulations from the Netherlands (520 W), Switzerland, and Austria (both 600 W).
Separately, as early as 2017, the German Solar Association (DGS) commissioned a specialized study from PI Berlin, which proved this power level was safe for electrical systems in German buildings. During the drafting of the VDE V 0126-95:2025-12 standard (2020–2025), increased PV module power and lower costs created clear market demand for higher-power balcony PV equipment. The 800 W specification, already adopted in Austria at the time, enjoyed strong popular support in Germany. Furthermore, the legal permissible upper limit for plug-in PV system capacity (module power) was already defined in the German Renewable Energy Act (EEG) as not exceeding 2 kWp. Therefore, Bergner’s main research objective was to investigate whether balcony PV systems with AC/DC power reaching 800 VA/2 kWp would significantly increase electrical safety risks. If so, the product standard would need to lower these limits further.
- Considering only the balcony PV’s output, since 800 VA is less than the power of many household appliances, its risk is lower.
In reality, the potential safety risk of balcony PV systems stems mainly from the impact of the balcony PV output current superimposing with the grid power.
Unlike rooftop distributed PV systems, balcony PV devices connect directly to existing final circuits and can be in parallel with other parts of the circuit, as shown in the following diagram. The current in conductor B may be the sum of the currents from A (grid) and C (balcony PV). Conductor B was not originally installed to carry additional balcony PV current. Thus, in an extreme scenario, one must assess whether superimposing the maximum grid current and maximum balcony PV current on conductor B could lead to fire or other hazards from line overload.
Diagram: PI Berlin
3️. In Germany, conventional final circuits (excluding those for high-power appliances) use 1.5 mm² copper wire. According to the VDE 0298-4 standard, its rated current In is 16 A, and the maximum continuous current is In × 1.13, i.e., 18.1 A. The standard requires that overcurrent protection devices must not operate within at least one hour at this current.
The 800 VA output of the balcony PV corresponds to a current of 3.48 A. Therefore, in the worst-case scenario described, the maximum current in conductor B is approximately 21.6 A. This operating condition is termed the “Maximum Foreseeable Load” or GAB.
It should be noted that GAB is a theoretical condition almost impossible in actual household electricity use.
Using German meteorological data, Bergner simulated the typical annual generation of a balcony PV system with 2 kWp installed capacity and an 800 VA inverter grid-connection power. From the annual generation curve, he calculated the output current at different times and superimposed it with the maximum continuous grid current of 18.1 A to obtain the maximum total current at each moment, as shown below.
Diagram: DKE
A more intuitive current intensity duration distribution diagram plots current intensity on the horizontal axis against the total annual duration (in minutes, logarithmic scale) on the vertical axis (see below). It shows the current intensity reaches 21.6 A for over 1,000 hours (60,000 minutes) annually, a result of the PV system’s high DC-to-AC ratio.
Diagram: HTW Berlin
Assuming conductor B is installed using the A2 method¹, the maximum temperature rise at point B is calculated with the formula from the PI Berlin 2017 report:
ΔT = 0.0615 * I^(2.3347).
Assuming an ambient temperature of 25°C, for a maximum continuous current of 18.1 A, the maximum temperature rise of conductor B is 53°C, reaching 78°C. After superimposing the 3.5 A PV current, the maximum temperature rise becomes 80°C, reaching 105°C.
Subsequent calculations revealed that the total annual duration where conductor B reaches 105°C exceeds 10,000 minutes. This duration is less than the time the current reaches 21.6 A because PV generation is fluctuating, which shortens the GAB condition and prevents the wire from reaching peak temperature.
Diagram: HTW Berlin
105°C is far below the ignition point of common building materials. For example, PVC, often used for wire insulation, ignites at 390°C. This indicates fire risk can be ruled out even under extreme GAB conditions.
However, 105°C exceeds PVC’s long-term operating temperature limit, accelerating its aging. In theory, this suggests balcony PV systems could increase the risk of insulation failure in conductor B. Bergner’s later research has largely addressed this concern.
4 Unlike theoretical extremes in electrical standards, real life rarely sees a specific 1.5 mm² copper conductor in a home sustaining an 18.1 A grid current for extended periods.
Using typical German household electricity load curves from prior HTW research, Bergner combined these with balcony PV generation curves to simulate maximum load scenarios a final circuit with balcony PV might encounter in practice. The diagrams below show the duration distribution of conductor current intensity (logarithmic scale, minutes) and the duration distribution of conductor temperature (minutes, durations below 60°C omitted).
Diagram: HTW Berlin
Diagram: HTW Berlin
The current intensity distribution shows that after installing a balcony PV system (green line), the duration of high currents (above 8 A) in the conductor is actually less than before installation (blue line). This is because the balcony PV outlet and high-power appliances are typically on different conductors, and the PV output can partially offset grid demand. The temperature distribution shows the annual duration above 95°C is only on the order of minutes, and high-temperature durations after installation (green) are shorter than before (blue). The overall temperature distribution after installation is also slightly lower. In short, the conductor runs cooler with a balcony PV system.
5.Based on the temperature data, Bergner calculated the probability of a balcony PV system causing a fire. Results show that installing five million balcony PV systems in Germany would leave the probability of an electrical fire essentially unchanged from before installation.In summary, the safety of 2 kWp/800 VA balcony PV systems can be distilled to two points:
- The additional fire risk is negligible.
- The risk of conductor insulation aging failure theoretically increases, but for typical household electricity use, this risk remains largely unchanged.
¹ The A2 method involves installing the wire within the wall’s thermal insulation layer. Among common installation methods, it has the poorest heat dissipation and leads to the highest cable temperatures.
- Technical Rationale for the Balcony PV VDE Standards Part 2: Inverter Requirements
The German balcony photovoltaic product standard VDE V 0126-95:2025-12 includes requirements for rapid shutdown performance of inverters. The primary technical research work for this section was carried out by Hermann Laukamp of the Fraunhofer Institute for Solar Energy Systems (Fraunhofer ISE), a member of the standard drafting committee. The inverter samples used for testing were provided by another committee member, Marcus Vietzke of Indielux GmbH. Below is an introduction to this research work.
2.1
Balcony PV systems impose additional requirements on inverter shutdown performance because the inverter’s AC output plug may be plugged in or unplugged while live, and the inverter has some capacitance. After unplugging, the residual voltage and residual energy at the plug contacts should not pose an electric shock hazard. Here, Laukamp referred to Clause 22.5 of the household appliance safety standard VDE 060335-1: within 1 second after the plug is removed, the residual voltage at the contacts shall not exceed 34 V. (Note 1) Inverters that do not meet the voltage condition above are still considered safe by Laukamp and the standard drafting committee if the residual energy after plug removal does not exceed 350 mJ. (Note 2) The image below shows the test setup built by Laukamp:Source/Image: DKE
During testing, Laukamp found that for some inverters, the time for the residual voltage to decay to 34 V exceeded 1 second. As shown below, the magenta curve on the oscilloscope screen represents the voltage change at the inverter output, and the yellow curve is the trigger signal.
Residual voltage test curve. The inverter plug is in an open-circuit state after triggering. Source/Image: DKE
A typical plug residual energy test result is shown below. After shutdown, the residual current and power drop rapidly to zero. The residual voltage first rises quickly and then gradually decays to zero within a few tens of milliseconds. Residual energy is the integral of power over time.
Voltage (blue), current (green), and power (magenta) curves from the residual energy test. The inverter output is connected to a 1.2 kΩ resistor (simulating the human body equivalent impedance). Source/Image: DKE
Among the 13 inverter samples tested, five had a residual voltage decay time to 34 V greater than 1 second.
The chart shows the residual voltage decay time to 34 V for different inverter samples. The vertical axis is time (in seconds). The blue bars indicate the test average, the orange bars show the test maximum, and the red line marks 1 second.
Source/Image: DKE
Only one sample, from the Letrica brand, had an average residual energy measurement exceeding 350 mJ (this sample’s residual voltage decay time was less than 1 second).
The chart presents residual energy test results for different inverter samples. The vertical axis is energy (in mJ). The blue bars represent the test average, the orange bars the test maximum, and the red line corresponds to 350 mJ.Source/Image: DKE
Based on the above test results, all 13 samples tested were deemed compliant with the inverter safety standard for balcony PV systems.
Note 1: The German standard VDE 60335-1 is derived from the IEC 60335-1 standard. The following is excerpted from IEC 60335-1:2020:
22.5 Appliances intended to be connected to the supply by means of a plug or via inserted pins shall be constructed so that in normal use there is no risk of electric shock when the pins are touched, for capacitors having a capacitance equal to or greater than 0.1 μF connected between any two pins.
Compliance is checked by the following test.
The appliance is supplied at rated voltage. Any switch is then placed in the off position and the appliance is disconnected from the supply at the instant of a voltage peak. One second after disconnection, the voltage between the pins of the plug is measured with an instrument having an input impedance of not less than 100 MΩ in parallel with an input capacitance of not more than 25 pF. The voltage shall not exceed 34 V.
If compliance depends on the operation of electronic circuits, the tests for electromagnetic phenomena of 19.11.4.3 and 19.11.4.4 are applied to the appliance one by one. The test for measuring the voltage between the pins of the plug is then repeated three times, the voltage not exceeding 34 V on any occasion.
Note 2: The following is excerpted from IEC 60335-1:2020:
8.1.4 An accessible part is not considered to be live in the following cases.
The part is supplied at safety extra-low voltage provided that, for alternating current, the peak value of the voltage does not exceed 42.4 V. For direct current, the voltage does not exceed 42.4 V.
Or the part is separated from live parts by protective impedance. If protective impedance is used, the current between the part and supply shall not exceed 2 mA for direct current and its peak value shall not exceed 0.7 mA for alternating current. The capacitance shall not exceed 0.1 μF for voltages having a peak value exceeding 42.4 V up to and including 450 V. The discharge shall not exceed 45 μC for voltages having a peak value exceeding 450 V up to and including 15 kV. The discharge energy shall not exceed 350 mJ for voltages having a peak value exceeding 15 kV.
Compliance is checked by measurement, the appliance being supplied at rated voltage. Voltage and current are measured between the part concerned and each pole of the supply. The discharge is measured immediately after interruption of the supply. The charge and energy of the discharge are measured with a resistor having a nominal non-inductive resistance of 2 000 Ω. The charge is calculated from the sum of all areas recorded on the voltage/time diagram, irrespective of voltage polarity. Details of a suitable circuit for measuring current are given in Figure 4 of IEC 60990:2016.
It appears that the safety criterion used by Laukamp—where a discharge energy not exceeding 350 mJ is considered safe—likely does not originate from Clause 8.1.4 but has another source. That’s because in Clause 8.1.4, the 350 mJ discharge energy corresponds to voltages with a peak exceeding 15 kV, not civilian low-voltage AC (with a peak of about 325 V).
Technical Rationale for the Balcony PV VDE Standards Part 3: choosing not to Copy Practices from Other Countries
In Part 1, “Technical Basis of the VDE Balcony PV Standard (1): Power Limit,” it was noted that when Germany developed its balcony PV standard, it drew on the practical experience and power regulations for balcony PV systems in countries such as the Netherlands, Switzerland, and Austria. Upon further investigation, however, the author finds that from an electrical safety perspective, balcony PV systems in those countries are fundamentally different from those in Germany. One cannot simply conclude that because such systems have a good safety record in those nations, they are equally safe in Germany or elsewhere. Why is this? Below is a comparison of residential final-circuit conductor specifications for several European countries and the International Electrotechnical Commission (IEC). For the same 1.5 mm² copper conductor, the rated current is 13 A in Austria and Switzerland, but 16 A in Germany. This means that under Swiss or Austrian electrical standards, the conductor’s electrical safety margin is 3 A greater than in Germany (a lower rated current permits a smaller connected appliance load, resulting in a larger electrical safety margin for the conductor).
Notes: (1) Based on pre‑2015 old standards; (2) Converted from 30 °C values; (3) Minimum value (installation method A2); (4) “?” = unknown, presumed to be the IEC value at 25 °C ambient temperature.
According to Germany’s DIN VDE 0298‑4 standard, at an ambient temperature of 25 °C, a continuous current of 16.5 A through a 1.5 mm² copper conductor is considered to pose no overload risk. If this standard holds true, then for Switzerland and Austria a balcony PV system with a grid‑connected output of 800 W (corresponding to 3.5 A) would present no conductor overload risk. This is fundamentally different from the scenario argued when Germany formulated the balcony PV standard VDE V 0126‑95—namely, the overload risk from a continuous 21.6 A current flowing through the conductor!
In the Netherlands, the standard copper conductor cross‑section for residential final circuits is 2.5 mm², with a rated current of 16 A. At 25 °C ambient temperature, the allowable continuous current is 18.3 A. Hence the Netherlands sets a maximum current for balcony PV at 2.25 A, corresponding to a grid‑connected power of 520 W. If the Dutch method for calculating maximum current were applied, Germany’s maximum balcony PV current and power would be only 0.5 A and 115 W, respectively.
To meet German market demands, the VDE balcony PV standard raised the grid‑connected power limit for balcony PV systems to 800 W, a move that has in fact departed from the original logic of the electrical‑standard framework. The technical risk is therefore theoretically higher than in the Netherlands, Switzerland, and Austria.
Moreover, Switzerland’s grid‑connected power limit for balcony PV is 600 W, not 800 W. Switzerland set this limit after comprehensively considering the allowable continuous current for a 1.5 mm² copper conductor at 22 °C (2.3 A), the permissible current for the Euro‑standard 50075 plug (2.5 A), and the Dutch balcony PV standard (2.25 A)—a relatively cautious approach. Austria’s maximum grid‑connected power for balcony PV is 800 W.
Image: Mariana Serdynska/Shutterstock
China’s household appliance safety standard GB/T 4706.1‑2024 is based on IEC 60335.1‑2016, and its cable rated‑current requirements are consistent with the IEC. Should China develop a balcony PV standard, the author hopes the relevant parties will examine the VDE balcony PV standard objectively and conduct rigorous, independent scientific analysis of its content. After all, residential electricity prices and labor costs in China differ vastly from those in Germany, and balcony PV in China remains more of a luxury than a necessity at present.
Main reference for this article: the 2019 report “STECKERFERTIGE, NETZGEKOPPELTE KLEINST‑PV‑ANLAGEN” by Dr. Thomas Erge et al. of the Fraunhofer Institute for Solar Energy Systems (Fraunhofer ISE), Germany.
