There’s a useful factsheet on the open access obligations in Horizon 2020 at https://ec.europa.eu/programmes/horizon2020/sites/horizon2020/files/FactSheet_Open_Access.pdf.
Essentially, researchers have to self-archive (such as in ROAR) or choose a gold OA journal (which may involve a substantial charge), and in some areas also deposit their data in a suitable repository (such as the one we will have ready by the summer). Stephen Grace our internal expert is happy to talk researchers through the OA requirements, or check particular journals for compliance with the EU policy.
UEL Research, Innovation and Impact 