Castro's slow, tentative moves toward a market economy are likely to find the country's antiquated energy infrastructure cannot cope with a steady growth in consumption and demand.
Cuba's communist administration has been gradually introducing economic liberalization to reduce the government's wage bill and encourage more Cubans to become self-employed.
The economic liberalization comes with many caveats and preconditions to fulfill some communist ideals but it is spiking electricity demand as more Cubans set up businesses and shops.
This week's power outage affected several million of the 11 million Cubans, including most of Havana's 2.2 million residents.
The website of the state-run newspaper Trabajadores said the outage occurred as a transmission line between Ciego de Avila and Santa Clara developed a fault, interrupting power supplies between the western side of the island and the center of Havana.
Power outages have been endemic and frequent in Cuba, sometimes lasting several hours, but the latest interruption was the longest and hardest to repair.
Cuban authorities say the country's infrastructure has been weakened by lack of spare parts and alternative equipment, a result of prolonged sanctions, import cuts and a black market that isn't easily accessible to most Cubans.
Critics of the Raul Castro's administration say the outages are partly the result of mismanagement and depleted expertise.
Most of the power industry equipment predates the start of U.S. sanctions.
Interruptions in supply and power surges are commonplace. Cubans have responded to the problem by using surge protectors for everything from computers to refrigerators.
The Ministry of Basic Industry in a statement cited an "interruption" in a 220,000-volt transmission line between the cities of Ciego de Avila and Santa Clara, which caused the power outage.
At least three provinces were affected but technicians using emergency generators were able to restore power after repair work that lasted about 5 hours.
The Cuban power grid is a patchwork of various emergency generation systems deployed to repair the system battered in a hurricane in 2004.
This week's blackout was more widespread than other outages in recent times and pointed to the neglect and poor maintenance of power generation and distribution system. Cubans were warned of more power blackouts.
Brazil has offered to help modernize Cuba's power generation and hopes it may be able to use a share of any future spare capacity of electricity in Cuba to meet its own industrial demand. Sub-sea power distribution systems have been discussed.
Industry analysts say a refurbishment of the antiquated power generation and supply system could cost several billion dollars and require several years of work before completion.
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