The company cautioned that workers must check pumps, motors and other equipment before the electricity is turned on.
The electrical system is key in cooling the overheated reactors, which are leaking radiation. But it is likely to be days if not longer before the cooling systems can be powered up, since damaged equipment needs to be replaced and any volatile gas must be vented to avoid an explosion.
The U.N.'s nuclear watchdog said the situation at Fukushima remains very serious.
Temperatures in a pool for storing spent fuel have cooled down at the plant after workers pumped in 18 tons of seawater. If the water had boiled away, exposing the fuel rods, more radioactive steam could have been released.
The crisis was continuing to batter Japan's once-robust economy.
Three of the country's biggest brands - Toyota Motor Corp., Honda Motor Co. and Sony Corp. - put off a return to normal production due to shortages of parts and raw materials because of earthquake damage to factories in affected areas.
Toyota and Honda said they would extend a shutdown of auto production in Japan that already is in its second week, while Sony said it was suspending some manufacturing of popular consumer electronics such as digital cameras and TVs.
The Food and Drug Administration said Tuesday it will halt imports of dairy products and produce from the area of Japan where a nuclear reactor is leaking radiation.
The FDA said those foods will be detained at entry and will not be sold to the public. The agency previously said it would just step up screening of those foods.
Other foods imported from Japan, including seafood, still will be sold to the public but screened first for radiation.
Meantime, survivors of the quake and tsunami are burying their loved ones.
Japan's police agency says more than 9,300 people are dead after an earthquake and tsunami. Almost 13,800 are missing.
Among them is a 24-year-old English teacher from Virginia. The teacher is the first known American victim.
In California, service members' families living in Japan touched down at Travis Air Force Base outside Sacramento Tuesday morning. More flights out of Japan are expected at bases across the country as military families escape the devastation.
The Associated Press contributed to this report.