This is an important point to consider. However, to me it seems somewhat separate from your previous comment.

Of course, no sane government should push for a country to rely solely on wind and solar. Ideally you have a mix of various energy sources, even potentially including some fossil fuels. Hitting that 20-30% sweetspot, as mentioned in the paper, looks to be fairly cheap and beneficial for everyone.

True, batteries are quite expensive and very much not environment-friendly when built on such a scale. Though it should be noted good solar panels last longer than 15 years. Even cheap panels can last 20 years.