Putting it in very simple terms, you can't just 'nip over' to Spain for a year any more.
After 90 days you would be in breach of immigration rules. That in itself could result in a future Residency application being refused.
If you have decided to move to Spain, or thinking about it, that's a big life changing decision that needs careful consideration because it has serious ramifications, in particular you lose UK health care, need Private Health Insurance in Spain and become tax resident in Spain. Plus you need to meet the financial savings/income criteria. It needs a lot of research and contemplation.
It can be done, you just need to understand how it works, so if you want to know more keep asking questions, there's lots of helpful and patient people here.
Steve