The thing with cats, particularly in a country where there is a (smaller) population of native wild cats which are similar to domestic ones and which the local birds evolved alongside, is that the birds they kill tend to be old, sick or injured and therefore unlikely to survive to the next breeding season and reproduce successfully. So while cats do kill birds, they don’t appear to have much of an effect on the population long-term.
In contrast, as far as I know healthy birds are no less likely to fly into wind turbines (or windows).
(Of course, this may well be different somewhere like Australia or even most of North America, where the birds didn’t evolve alongside domestic-cat-sized feline predators).
EDIT: It turns out there are no wild cats in Norway- Scandinavia and Ireland are the only parts of Europe where they haven’t been recorded historically, though there have been feral domestic cats there for over 1000 years.
