Water supplies to Baghdad have also been cut off for days at a time, with summertime pressures on key systems said to be more intense than ever.
The ministry blamed poor maintenance, fuel shortages, sabotage by insurgents and rising demand for the problems, and said some provinces hold onto supplies.
The US Army told the BBC that Iraq must now take charge of fixing the problems.
The general in charge of helping Iraq rebuild its infrastructure, Michael Walsh, said that although Iraqi authorities only have one-quarter of the money needed for reconstruction, solving the problem was now up to them.
Gen Walsh told the BBC that the US had jump-started reconstruction but that, working with donor nations, the Iraqi government needed to do the rest.
The Iraqi warning came a week after the charity, Oxfam, and a coalition of Iraqi NGOs reported that nearly one-third of Iraq's population was in need of immediate emergency aid.
Their report suggested 70% of Iraqis did not have adequate water supplies and that only 20% had access to effective sanitation.
A spokesman for the electricity ministry said Iraq's electricity system was only meeting half of the demand and that there had been four nationwide blackouts last week.
Aziz al-Shimari said the shortages were the worst since the summer of 2003, shortly after the US-led invasion overthrew Saddam Hussein.
Baghdad residents are complaining that the situation this summer is even worse than four years ago, correspondents say.
Poor maintenance and a lack of diesel fuel have left even newly-refurbished power stations working below capacity.
The continuing threat of damage by insurgents has also been a challenge, with 15 of the 17 high voltage lines running into Baghdad have been sabotaged.
"When we fix a line, the insurgents attack it the next day," Mr Shimari told the Associated Press.
The problems have been compounded by provinces holding onto supplies for themselves rather than powering Baghdad.
"Many southern provinces such as Basra, Diwaniya, Nasiriya and Babil have disconnected their power plants from the national grid. Northern provinces, including Kurdistan, are doing the same," Mr Shimari said.
"We have absolutely no control over some areas in the south."
Mr Shimari warned that the national grid would collapse if the provinces did not "abide by the rules".
"Everybody will lose and there will be no electricity winner," he said.
Baghdad's water supply has also been severely affected by failing power supplies.
New water treatment plants are working, but a lack of power and broken pipes mean that the water is easily contaminated and hardly flows at all in many places.
© BBC MMVII