Cuba plans to close more than 100 factories for all of October as part of a plan to deal with power shortages.
Fidel Castro has called for public understanding
Other measures to save energy include a shorter working week, reduced street lighting and scheduled power cuts.
The power shortages have caused a range of problems - affecting the flow of drinking water in homes and causing fridges and freezers to stop working.
President Castro said the trouble was caused by problems at Cuba's main power station, not the high price of oil.
"An electrical system that has all these problems is a weak system," Mr Castro said.
The president promised to invest in new generating capacity, but warned the problems could continue for five months or more.
"The co-operation of the public is very important," he said.
Western diplomats say Cuba is finding it difficult to make the investment its power system needs, because of a US trade embargo.
To help cope with the crisis, 118 factories, including steel plants, sugar mills and paper processors will be shut for the whole of October, said Vice-President Carlos Lage.
The average eight-hour government work day will be cut by 30 minutes and school classes will start half-an-hour later.
The disappearance of Soviet aid following the collapse of the USSR forced the Cuban government to introduce tight rationing of energy, food and consumer goods.