average, a wind farm planning application takes two years to be considered by a local authority, with an approval rate of 40%. This compares extremely unfavourably with other types of major applications, such as housing, retail outlets and roads, 70% of which are decided within the 13- to 16-week statutory deadline; for wind farms the rate is just 6%. Approximately half of all wind farm planning applications, over 4GW worth of schemes, have objections from airports and traffic control on account of their impact on radar. In 2008 NATS en Route, the BWEA, the Ministry of Defence and other government departments signed a Memorandum of Understanding seeking to establish a mechanism for resolving objections and funding for more technical research. Wind farms in the UK often have to meet a maximum height limit of (excluding Scotland). However, modern lower cost wind turbines installed on the continent are over tall. This planning criteria has stunted the development of onshore wind in the UK. List of the largest operational and proposed onshore wind farms Economics Subsidies and taxes From 2002 to 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 1ROC per MWh, but since the Renewables Obligation Banding Review in 2009, offshore wind has received 2ROCs to reflect its higher costs of generation. In Northern Ireland, a banding of 4 ROCs is available for small onshore turbines. Wind energy received approximately 40% of the total revenue generated by the Renewables Obligation, and ROCs provided over half of the revenue of the wind farms involved. The total annual cost of the Renewables Obligation reached £6.3billion in 2019–20, of which 67% was for wind power. This cost was added to end-user electricity bills. Sir David King warned that this could increase UK levels of fuel poverty. The government closed the Renewables Obligation to new onshore wind power projects in 2016. Support for offshore wind was moved into the government's Contract for Difference (CfD) regime. Support for wind power under this programme rose to £1.7billion in 2020, with £1.6billion of that total shared between six offshore