Disconnecting the antenna would still have leakage at close range. Grounding the antenna might be a better option. But in practice, the dangers highlighted by the article only surface when an attacker has control of many solar plants at scale.

Compromising an individual one by getting close-range physical access will be a local annoyance but wouldn't scale to a level where it can threaten the grid, so it limits the pool of potential attackers to local vandals (which can achieve their goals easier by just throwing rocks at your panels).