SHANGHAI, Aug 22 (SMM) - The costs of aluminium smelters remained largely stable last week. Coal prices rose due to output cuts by coal mines in Inner Mongolia and Shanxi, but the power costs of smelters with captive power plants remained unchanged due to slow price transmission and the fact that their power plants have not used up the coal bought earlier. Meanwhile, the electricity prices of smelters who use grid power were also stable. Alumina prices fell in south-west China, but rose in Henan and Shanxi. The real-time costs of smelters dropped 17.6 yuan/mt from a week ago to 17,812 yuan/mt last Friday, while their profits shrank 232 yuan/mt to 608 yuan/mt. The SMM spot aluminium prices stood at 18,420 yuan/mt. Given the summer peak of power use and decline in thermal coal supply, the electricity prices are unlikely to fall in the short term. Alumina prices may fall slightly. The short-term aluminium costs will remain high.