In reply to Duncan Campbell:
There are no shortcuts to this so you and your group will need to invest some time and energy before the debate.
Consider conduting a mock debate using your half of the group to see how the discussion might ebb and flow.
How will the opposing group construct their argument?
What is the legitimacy of their likely source material (and yours)?
If you were defending wind farms what questions would you and your team struggle to answer?
Etc..