* Sept aluminium output at 2.79 mln T, lowest since May
* Aluminium prices fell by 4.2 pct last month
* Input costs rise on captive power plants reform (Updates throughout)
BEIJING, Oct 19 (Reuters) - China’s primary aluminium production fell for a second straight month in September and slid to its lowest level since May, as weaker aluminium prices and higher input costs led smelters to cut back output.
The world’s top aluminium producer churned out 2.79 million tonnes of the metal last month, according to data from the National Bureau of Statistics released on Friday.
That was down 1.8 percent from 2.84 million tonnes in August, but up 7.1 pct from a year ago.
On a daily basis, China produced around 93,000 tonnes of primary aluminium last month, according to Reuters calculations based on the data. September had one day fewer than August.
Aluminium prices on the Shanghai Futures Exchange fell by 4.2 percent in September, whereas spot prices for alumina, the substance used to make the metal, in the smelting heartland of east China region SMM-ALM-ECHN nudged up another 0.8 percent after climbing by 10.8 percent in August.
Furthermore, east China’s Shandong province last month said it had started charging owners of captive power plants, which include major aluminium smelters, fees for electricity generated using the plants, raising their production costs.
Key aluminium centres in Shandong have avoided a repeat of last year’s 30 percent blanket cuts to production in the coming winter, but are still waiting to hear what restrictions are to be set by their city governments.
In the first nine months of the year, China produced 25.0 million tonnes of aluminium, a rise of 4.2 percent from the same period last year, the data showed. (Reporting by Tom Daly and Muyu Xu; editing by Richard Pullin)