The share of renewables in the country's electricity generation has risen from below 2% in 1990 to 14.9% in 2013, helped by subsidy and falling costs. Introduced on 1 April 2002, the Renewables Obligation requires all electricity suppliers who supply electricity to end consumers to supply a set portion of their electricity from eligible renewables sources; a proportion that will increase each year until 2015 from a 3% requirement in 2002–2003, via 10.4% in 2010-2012 up to 15.4% by 2015–2016. The UK Government announced in the 2006 Energy Review an additional target of 20% by 2020–21. For each eligible megawatt hour of renewable energy generated, a tradable certificate called a Renewables obligation certificate (ROC) is issued by OFGEM.