On average, around the world, it takes some 15.7 kWh of electricity to produce one kilogram of aluminium from alumina. Design and process improvements have progressively reduced this figure from about 21kWh in the 1950's. In some smelters this spare heat is used to melt recycled metal. Blending recycled metal with new metal allows considerable energy savings, as well as the efficient use of process heat. There is no difference between primary and recycled aluminium in terms of quality or properties.
Many locations are remote and the electricity is generated specifically for the aluminium plant.
The smelting process is continuous. A smelter cannot easily be stopped and restarted. If production is interrupted by a power supply failure of more than four hours, the metal in the pots will solidify, often requiring an expensive rebuilding process. From time to time individual pot linings reach the end of their useful life and the pots are then taken out of service and relined. The marginal difference in the purities of smelter grade aluminium and super purity aluminium results in significant changes in the properties of the metal .