The Australian Energy Market Operator oversees the nation’s power markets. Chief among them, the National Electricity Market serves about 90 percent of customers, minus remote areas and the west coast. At its peak, the system uses 38 gigawatts of power—more than New York state’s peak consumption. Over the last five years, AEMO has rigorously studied how the country, whose coal fleet is aging and which banned nuclear energy decades ago, can run this grid on renewables alone.