What's more common is that they don't have the transmission capacity itself, but that one's pretty easy in this case too, because what that means is that you have an existing transmission line which is already near capacity with generation on one end and customers on the other. So then you just build the data center on the end of the transmission line where the generation is rather than the end where the existing customers are, at which point you can add new generation anywhere you want -- and if you put it near the existing customers you've just freed up transmission capacity because you now have new customers closer to the existing generation and new generation closer to the existing customers.
> The Dutch power grid is already almost 50% renewables
I calculate about 43.5% was solar or wind. What is way crazier is the "bend in the curve" of production sources in the last 10 years. Look here at how fast solar and wind is growing! https://en.wikipedia.org/wiki/File:Netherlands_electricity_g...
In most other places the percentage is significantly less than that and then you can easily add more of the cheap-but-intermittent stuff because a cloudy day only requires you to make up a 10% shortfall instead of a 50% one, which existing hydro or natural gas plants can handle without new storage when there are more of them to begin with.