Damages following breaches of EU law

My research focuses on the "European law of damages"; which requirements does European Union law set for national courts when deciding on civil remedies following breaches of European-law-derived rights?
So far, we see widely diverging outcomes in terms of damages awards in different European countries, even if the breach of EU law was essentially the same. This will only become more concerning with the emergence of collective actions, as such differences between countries will then often also determine where collective actions will be brought and where citizens may instead remain without effective and cost-efficient legal recourse. How can we create more consistency and predictability in the European law of damages?