You are

Producer
You are a producer when you have an installation that generates renewable electricity, heat or if you generate electricity from fossil sources.

Trader
A trader is an organisation that trades in certificates.

End user
An end user has an account at CertiQ to keep precise track of the certificates that a trader  cancels on behalf of the end user.

Intermediary
An intermediary defends the interests of organisations or individuals with sustainable production facilities or with more traditional fossil-based facilities.