ILOILO CITY, Philippines ? The Visayas is expected to have power interruptions for at least a week starting Monday due to the shutting down of a major plant in Leyte for maintenance purposes.

The National Grid Corp. of the Philippines (NGCP), in an advisory on Sunday, said preventive maintenance services on the 120-megawatt Mahanagdong geothermal power plant started on Saturday and was expected to last for 10 days.

The Visayas grid, which gets the bulk of its power supply from Leyte, will suffer a decrease in supply up to 200 MW also because of the shutting down of other major plants in Cebu, which are undergoing maintenance services, according to NGCP Visayas corporate communications officer Belinda Sales-Canlas.

The drop in supply is expected during peak hours on weekdays starting Monday and will be distributed among major island and cities in the Visayas.

The Visayas grid covers Western Visayas (Aklan, Antique, Capiz, Guimaras, Iloilo, and Negros Occidental), Central Visayas (Bohol, Cebu, Negros Oriental, and Siquijor) and Eastern Visayas (Biliran, Leyte, Southern Leyte, Northern Samar, Samar, and Eastern Samar).

The regions have a total population of around 17 million based on the 2007 census.

The Visayas for years have already been experiencing rotational brownouts due to a critical power situation.

The power plants in the Visayas have a dependable capacity (maximum output that a power plant can provide at any specified condition and time) during the evening peak of around 1,215 MW (as of July last year).

This is just slightly more than the peak demand during that day reaching 1,143 MW, according to the Department of Energy Industry Management Division of the DOE Visayas Field Office.

Leyte?s geothermal plants supply the bulk of the Visayas grid through submarine cables. It has a dependable capacity of 576 MW but Leyte-Samar only needs 184 MW at its peak demand. The surplus of 399 MW is exported to Bohol, Cebu, Negros, Panay, and, during off peak, to the Luzon grid.