The fragility of Australia’s National Energy Market was highlighted again over the weekend, when unit one of Victoria’s Yallourn coal-fired power plant tripped on Saturday afternoon.

The unscheduled outage took nearly 400MW of generation capacity out of the mix and leaves the state a total 940MW short, with 560MW of capacity still missing from AGL Energy’s Loy Yang A plant, which tripped unexpectedly in October.

The combination of the coal power outages has prompted the market operator to issue a Forecast Lack Of Reserve Level 1 (LOR1) in the state for Tuesday and Wednesday – AEMO’s first step towards warning of a potential supply shortage – with temperatures forecast to reach 32°C in the state and stay there for most of the week.

LOR1 are not considered a threat to supplies – that doesn’t happen until an LOR3 – but it is unusual for this time of year.

unit 1 at yallourn tripped yesterday. sudden loss of ~380MW — huge.#CoalBeingReliable pic.twitter.com/TxI63APFzc

— simon holmes à court (@simonahac) November 18, 2017

The events underline that the biggest risk to energy supplies this summer are not variable renewable energy generation, but the failure of country’s ageing fossil fuel generators in the mid-summer heat.

Considering we are technically still in Spring, the current situation does not bode well.

AEMO is still yet to be advised on when AGL’s Loy Yang A generator will be back in the mix.

The unit went offline unexpectedly two days before a planned 40-day unit maintenance outage, after it experienced a unit trip due to a generator fault. There are fears that the problem with the generator could run deep.

Update: The LOR1 was later cancelled by AEMO after a market response to the potential shortfall, as is usually the case. LOR2 and LOR3 events signal more urgent responses are needed.

Update 2: On Tuesday AEMO issued a next level LOR2 advice, seeking a market response and warning of possible intervention if the shortfall was not met.