Therefore, 230 * 20 = 4,600 watts that your generator will need when running.
However, a compressor is a inductive load device, and the same as a fridge when it first comes on, lights dim and there's a power inrush until the motor comes up to designed speed. So while it comes up to speed it sucks more current than at normal running speed.
And this lower run current (start up inrush) must be factored into the generator's size.
Honda.ca show this in their generator chart.
So you will wind up selecting a generator bigger than the compressor's running watts to cover the start up load, and then maybe go to the next size bigger for winter compressor use when both the generator oil and the compressor oil is thicker - it could use the next size up to handling the load, help like having a big V8 under the hood, even though a 6 cylinder might do the job.