Electricity prices for Chilean residents on the central SIC power grid will retroactively decrease an average of 1.3% from July, the government's National Energy Commission said Friday.

Residential rates are indexed to wholesale electricity prices, or node rates, which are calculated using international fuel prices, local generation costs, the peso's exchange rate against the dollar, water reservoir levels and utilities' capital expenditures, among other factors.

Chile imports nearly 98% of the fossil fuels it consumes.

For an average home consuming 150 kilowatt hours a month, the electricity bill will decrease to 15,682 Chilean pesos ($33.17), from CLP15,896.

The SIC grid provides power to 90% of Chilean homes from the northern city of Taltal to the southern island of Chiloe.

The main power companies supplying energy to the SIC grid are Empresa Nacional de Electricidad SA (EOC, ENDESA.SN), AES Corp. (AES) through its AES Gener SA (AESGENER.SN) unit, and Colbun SA (COLBUN.SN).

Chile's Energy Ministry adjusts wholesale electricity rates every six months, resulting in increases or decreases in the price charged to regulated customers, including residential clients.

The commission can also readjust rates between these dates if any of the factors it takes into consideration vary more than 10% during the six-month period in which the regulated prices are valid.

Write to Graciela Ibanez at graciela.ibanez@dowjones.com