That's a rather broad vague statement. While I don't think there is any debate that renewables do pose some challenges for grid operators, there are many grids all over the world with high wind and/or solar concentrations and very few problems. South Australia has a very impressive number of 70%, renewable, and that is without hydro. Then there is the example of texas, which I think frequently runs on a majority of wind power. I don't understand the "this has some challenges so we shouldn't do it and just stick with the old way" philosophy.
Here is a video on South Australia if anyone is interested.