completed in January 2000. The most obvious external change was the two-story glass extension on one half of the roof. Much of the original internal structure remained, including the cavernous main turbine hall, which retained the overhead travelling crane. An electrical substation, taking up the Switch House in the southern third of the building, remained on-site and owned by the French power company EDF Energy while Tate took over the northern Boiler House for Tate Modern's main exhibition spaces. The history of the site as well as information about the conversion was the basis for a 2008 documentary Architects Herzog and de Meuron: Alchemy of Building & Tate Modern. This challenging conversion work was carried by Carillion. Opening and initial reception Tate Modern was opened by the Queen on 11 May 2000. Tate Modern received 5.25 million visitors in its first year. The previous year the three existing Tate galleries had received 2.5 million visitors combined. Extension project Tate Modern had attracted more visitors than originally expected and plans to expand it had been in preparation since 2004. These plans focused on the south west of the building with the intention of providing 5,000 m2 of new display space, almost doubling the amount of display space. The southern third of the building was retained by the French State owned power company EDF Energy as an electrical substation. In 2006, the company released the western half of this holding and plans were made to replace the structure with a tower extension to the museum, initially planned to be completed in 2015. The tower was to be built over the old oil storage tanks, which would be converted to a performance art space. Structural, geotechnical, civil, and façade engineering and environmental consultancy was undertaken by Ramboll between 2008 and 2016. This project was initially costed at £215 million. Of the money raised, £50 million came from the UK government; £7 million from the London Development Agency; £6 million from philanthropist John Studzinski; and donations from, among others, the Sultanate of Oman and Elisabeth Murdoch. In June 2013, international shipping and property magnate Eyal Ofer pledged £10m to the extension project, making it to 85% of the required funds. Eyal Ofer, chairman of London-based Zodiac Maritime Agencies, said the donation made through his family foundation would enable "an iconic institution to enhance the experience and accessibility of contemporary art". The Tate director, Nicholas