The official gave the figure on Tuesday during the investigative hearing of the Senate Ad-hoc Committee on Power.
He said inconsistent funding was responsible for the lack of constant electricity in the oil-rich nation.
Ambassador Igali, however, pointed out that the privatisation exercise, which took place in 2013, had helped in taking the burden of funding off the Federal Government.
The Senate committee also received a presentation on the National Integrated Power Project, which was conceived in 2004, as a major fast-track initiative to add significant new generation capacity to Nigeria’s electricity supply industry.
The Senate had said that the probe would cover the regimes of former Presidents Olusegun Obasanjo, late Umaru Yar’adua and Goodluck Jonathan.
The Senate Ad- hoc Committee on Power, was inaugurated by the Senate President, Dr. Bukola Saraki, on August 28.
The Clerk of the Committee on Power, Mr Cletus Ojabo, said the probe would be in form of investigative hearing and interactive session with key players in the sector.