The world’s biggest integrated solar power system that cost 277 million yuan ($45 million) to construct has stood idle for two years in Nanjing, Jiangsu province, China National Radio reported on Wednesday.

The system, with 30,000 solar batteries, was installed on the roof of Nanjing South Railway Station in 2011. It was supposed to make 6 million kWh a year, reducing coal demand by more than 2,000 tons.

However, it was not put into use in June 2011 when the railway station started operations, according to the National Audit Office’s report released last week.

The reason has not been made public.