An interesting article, and clearly it's right that wind and solar (at least in Europe) need backup from other sources that can be spun up for a few days when it's not windy across the continent. Now, if we factored in hydro (not pumped storage, which is mostly good for short term daily patterns, but conventional hydro), and reserved a significant part of it for these few days, perhaps adding additional turbines to existing dams to increase peak hydro power, how much difference would that make? Can we store enough water to fill in the gaps?