I'm not sure why all the downvotes, but overloading is true, see here how to avoid it:
https://balkon.solar/news/2025/03/17/how-does-plug-in-pv-in-germany-work/

Preventing Circuit Overload (Source + Load on One Circuit)

The key safety concern is that a plug-in solar inverter feeds into a final sub-circuit “downstream” of the main breaker. Normally, a circuit breaker senses all current on its circuit and trips if the load is too high. But with a PV source injecting current at a wall socket, part of the load is supplied locally. The breaker only “sees” the net current from the grid – not the portion supplied by the solar module . This means the wiring could carry more amps than the breaker’s rating without tripping. For example, on a 16 A circuit a 600 W micro-inverter (≈2.6 A) plus a 16 A appliance could theoretically pull ~18.6 A through the wires while the breaker sees only ~16 A . Over time, such an unseen overload can overheat cables, especially in old or unfavorable installations.

The 800 W limit (specified as 800 VA) was chosen as a conservative safe value so that typical 1.5 mm² house wiring can handle the extra current margin. Even under full sun, a 800 W unit rarely sustains peak output (often max ~500–550 W ≈ 2.4 A), and most circuits can tolerate that small extra current. The limit is rising to 800 W (≈3.5 A) as EU regulations consider <800 W “not significant” generation. At 800 W, German guidance still deems the slight increase manageable, but extra safety margins are advised. For example, in older homes with uncertain wiring, it’s recommended to replace the 16 A breaker with a 13 A one. A 13 A MCB will trip sooner, ensuring that the sum of grid + solar current can’t overheat the cables (13 A from grid + ~3 A PV ≈ 16 A total). Another strategy is having an electrician connect the balcony PV on a dedicated circuit with its own breaker, so it doesn’t combine with heavy appliance loads on the same line. Then even larger system would be possible.

In practice, users are advised to avoid overloading scenarios proactively: connect the mini-PV to a circuit that isn’t already near capacity, and never daisy-chain multiple PV units or plug them into extension strips . Only one unit per outlet/circuit is allowed, which prevents additive overcurrent from two inverters. By following these limits and using the existing circuit protection, Germany keeps wiring stress “within tolerance” . Notably, tests have shown that issues (excessive heating) would only start to appear above roughly 700 W sustained feed-in combined with a fully loaded 16 A circuit in worst conditions.