I recently watched a documentary about aluminum smelting and this topic came up. An engineer said that they have a 6 hours time frame. If the power doesn't come

I recently watched a documentary about aluminum smelting and this topic came up. An engineer said that they have a 6 hours time frame. If the power doesn't come back on, the aluminum hardened too much and all smelters are lost forever. There is no possibility for on-site generators because the required generator would be the size of a power plant.