Solar farm owners in south-eastern states are switching off their plants to protect their profits as extreme winds, abundant rooftop solar generation and low demand from customers enjoying the warm start to spring create an oversupply of power.

As wild winds in Victoria left more than 140,000 households without power on Monday, the curtailment of generation from solar farms reached almost 80 per cent in NSW as wholesale prices dropped to zero and below, according to electricity market expert Paul McArdle.