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South Australia on Sunday became the first gigawatt scale grid in the world to reach zero demand when the combined output of rooftop solar and other small non-scheduled generators exceeded all the local customer load requirements. Renew Economy reports: The landmark event was observed by several energy analysts, including at Watt Clarity and NEMLog, where Geoff Eldridge noted that a number of measures for South Australia demand notched up record minimums for system normal conditions. It was later confirmed by the Australian Energy Market Operator, which noted that "scheduled" demand -- local demand minus the output of rooftop solar and small unscheduled generators such as small solar farms and bio-energy -- fell to minus 38MW in a five minute period at 1235pm (grid time, or AEST). Minimum demand is now possibly the biggest challenge for market operators like AEMO, because under current market settings it needs to have a certain amount of synchronous generation to maintain system strength and grid stability. It does this by running a minimum amount of gas generation, and through the recent commissioning of spinning machines called synchronous condensers that do not burn fuel. It also needs a link to a neighboring grid, in this case Victoria, so it can export surplus production.