Hydro + Wind + Solar is a powerfull mix. Hydro tends to have fixed power per year, and a lot of flexibility when you release that power. Solar matches the daily demand in most areas, though Denmark is very far north to produce solar they can import solar from the south.

Wind is really cheap and provides some power 24/7 but does not match the demand curve. So even then you still needs some backup power either from pumped hydro or peaking power plants.

IMO, the real downside is the electric grid becomes even more complex to manage and takes real investments to handle shifting supply.