pumped storage
The energy density of pumped storage is extremely low. Wiki says a cubic meter of water in a 100m tower has about 0.272kwh. Adding in the losses of the turbines, pumps, and evaporation, it only gets worse. To last through the long cold calm spells you'd need to turn all of Scotland into a reservoir farm, destroying its ecology, and that might not even be sufficient. Pumped storage is good for smoothing output on the periodicity of a day or so, but anything longer requires alternative power solutions capable of the entire peak load on the system. If those alternative solutions aren't environmentally friendly, you still have a problem, and they are, why do you need wind?