If you have a circuit rated for 15 amps, and plug in 12 amps of solar, then the breaker won't trip until the circuit load exceeds 27 amps, which seems bad.
Hmm, if you have an appliance (like a clothes dryer) with a dedicated circuit, it seems like you could solve this by connecting there. If you have the balcony solar device plug into the wall and the appliance plug into the balcony solar device, then you can easily put an additional circuit breaker where it's needed.