Modern solar inverters communicate with the grid operators, less modern ones follow the grid frequency. The grid is allowed to deviate from UTC by a few seconds

Modern solar inverters communicate with the grid operators, less modern ones follow the grid frequency. The grid is allowed to deviate from UTC by a few seconds, in some edge cases it ramps up to minutes, but it eventually comes back in sync with UTC. Good enough for kitchen clocks, simple timers and the likes.