NEW YORK - Ghana's state-owned Volta Aluminium Co.'s Valco smelter in Tema shut half of a potline because of requests by the state power authority to reduce electricity use, said a spokesman for Alcoa Inc. on Friday.

Alcoa, the world's largest aluminum producer, owns a 10 percent stake in the West African facility and the impact of the shutdown was about 2,000 tonnes of the Alcoa's 8,000 tonne share of annual production.

"Production went from two potlines to 1-1/2 potlines in the past couple of days due to power shortages," said Alcoa spokesman Kevin Lowery.

He added that the Valco smelter's two potlines had been producing at a roughly 80,000-tonne-per-year annual output rate. With the curtailment, he said, the smelter is now operating at a rate of about 60,000 tonnes a year.

On Tuesday, the Volta River Authority, the wholesale power utility in Ghana, advised bulk electricity users of potential power shortages in the African country, and asked that they be prepared to reduce their electrical power consumption by as much as 25 to 50 percent.

VRA, which runs mainly on hydro power, cited water shortages affecting its power generating facility for the curtailed power supply.

In April, Alcoa's Lowery had said the 200,000-tonne-a-year smelter was restarted and metal was being produced, but lack of power supply was constraining output, he added.

Power shortages caused Valco to lower its 2006 production estimates to two potlines or 80,000 tonnes of aluminum from its original plan to restart three potlines representing 120,000 tonnes this year.

Valco is powered by energy from the Volta River Authority, but demand from the nearby capital city of Accra has increased faster than anticipated, causing blackouts and taking power supply needed at the smelter.