From 2002-2015, windfarms were subsidised through the Renewables Obligation where British electricity suppliers were required by law to provide a proportion of their sales from renewable sources such as wind power or pay a penalty fee. The supplier then received Renewable Obligation Certificates (ROC) for each MW·h of electricity they have purchased. The Energy Act 2008 introduced banded ROCs for different technologies from April 2009. Onshore wind receives 1 ROC per MW·h, however following the Renewables Obligation Banding Review in 2009 offshore wind then received 2 ROCs to reflect its higher costs of generation.