South Africa is considering extending the lives of some of its biggest coal-fired power plants as the government seeks to bolster the country’s long-term energy security amid a deepening crisis. Kendal and Lethabo, two plants that represent about fifth of the State-owned power utility’s current capacity, are possible candidates, according to people familiar with the matter. Officials tasked with ending the crisis and making sure it doesn’t recur are looking at all options, the people said, asking not to be identified as the plans aren’t yet public.