The global maintenance expenditure on wind turbines - vital to productivity - is expected rise from $9.25bn in 2014 to $17bn in 2020.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/wind-turbine-maintenance-costs-almost-double-2020
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/edie-uk
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/energy
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/wind-energy
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/renewable-energy
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/electricity
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/turbines