Renewables Obligation Certificates or ROCs – these are the UK government’s support mechanism for renewable energy projects in the UK (except for small schemes which are supported by Feed-in Tariffs).
The scheme started in 2002 in England, Wales and Scotland and 2005 in Northern Ireland.
Renewables Obligation Certificates are tradeable. They get awarded to operators of accredited renewable generating stations for the eligible renewable electricity they generate. Producers of renewable energy get given ROCs and every power producer must be able to produce ROCs in proportion to the power they produce. Fossil fuel power producers are forced to buy ROCs from the renewable energy producers and this provides a subsidy to the renewable energy producers.
The number of Renewables Obligation Certificates awarded to each producer varies according to how they produce electricity and when their plant was first commissioned. Early on in the life of the scheme the system was much more generous for producers of power from solar than it is today. Nowadays the most generous grants are available for wave and tidal power (up to a 30MW limit)- an area the government wants to encourage.
You can read more about the scheme here