SEC made a net profit of SR2.2 billion ($587 million) for the third quarter, compared with SR2.3 billion in the same period a year earlier. 

Analysts surveyed by Reuters expected the firm to post on average SR2.65 billion.

"The reason for the decline in the third quarter net profit compared to the same period a year earlier is mainly the rise in costs of the consumption and purchase of energy," the statement said. 

Operational profit for the third quarter declined by 3 percent to SR2.125 billion from SR2.195 billion in the third quarter a year ago. 

Saudi Arabia, OPEC's biggest oil exporter, is struggling to keep up with rising power demand, which is rising 7 to 8 percent annually amid a growing population of over 27 million. 

On Sunday, SEC signed a SR5.4 billion contract with an unnamed Saudi company to build 1,200 megawatts of power generation capacity at a plant in Riyadh.

The company, which has an installed capacity of 50,000 megawatts, plans to boost its capacity to at least 80,000 megawatts by 2020.