ROCs - Renewable Obligation Certificates are digital certificates awarded by OFGEM for each MWh of power produced from a certified renewable source.

ROCs are valuable to power suppliers because a rising proportion of the power that they supply has to be shown to come from renewable sources. Suppliers are fined if their target is not met.

As a power generator (such as R-Wind) the security of having a long-term contract to supply power and ROCs to a power supplier can be important - especially if that is a requirement imposed by the B/BS financing the turbine.

As time goes by - with more people participating - arrangements to sell power and ROCs will not be dictated and better terms can be negotiated as energy prices rise.

There are many uncertainties as to the future of the ROC system, but because so much investment has been made in turbines by powerful market players it is unlikely that dramatically adverse changes will take place in the next ten years.
'Google' for the gamut of opinion.