In simplified terms, most EU countries have either ample sun (Mediterranean area), wind and ocean (north, west ) or wind and space (Poland & neighbors). Most also have a coast, mountains or both so some hydro potential. Even Luxembourg managed to find thermal power for heating.

With wind turbines improving steadily and available in different sizes there is also no big barrier to having them interspersed. Germany or the Netherlands are in large parts densely populated but still manage to put up wind turbines everywhere.

The UK has 275 inhabitants per square kilometer, the EU has 102 inhabitants per square kilometer.