How rooftop and big solar are pushing coal out of daytime energy market

One of the most common questions among people concerned about climate change and cleaning up the energy grid, is what small contribution they can make. Will adding rooftop solar make any difference at all?

The answer is most certainly yes. The latest quarterly report from the Australian Energy Market Operator contains little doubt – the increase in rooftop solar, and in large scale solar plants, is pushing coal out of the daytime market.

According to the Quarterly Energy Dynamics report for the December quarter, the changes in generation sources for the main grid was quite marked.

This graph below shows the increase in average output from rooftop solar (light orange), large scale solar (yellow), wind (green) and gas (grey) in the fourth quarter of 2019, compared to the fourth quarter on 2018. Below the line are the reductions in black coal and hydro.

The biggest increase – and remember this is not average output, but the average increase in output – came from rooftop solar, which in 2019 posted a record installation rate of 2.13GW (for sub 100kW systems). Rooftop solar at its midday peak posted an average increase of more than 1.5GW over the quarter, showing the real impact on the generation mix.

The coal generators most affected by the increase in solar output – both rooftop and large scale – were Eraring in NSW, where output declined by an average 231MW, and Gladstone and Stanwell in Queensland, where the average middle of the day output declined by 246MW.

Other coal generators might also have been affected, but their output was interrupted by so many outages – both planned and unplanned – it was hard to tell.

This graph above shows the impact on Eraring, showing that the daytime output was at time 400MW below the same quarter a year earlier.

The Victoria Energy Policy Centre has written an interesting piece on how the reduction in Eraring output was managed by its owners, Origin Energy, and how some capacity was bid higher than usually more expensive gas, which resulted in an increase in prices, and profits, in another case of the incumbents exercising market power.

In Queensland, the increased output of rooftop and large scale solar has resulted in changing pattern of charging by the state’s biggest pumped hydro facility at Wivenhoe, which is now under new ownership by the government owned CleanCo.

Under its previous owner, Cleanco pumped mainly at night, supporting coal generation, but with CleanCo it is now doing most of its pumping during the day, soaking up the excess of cheap solar – the so-called solar duck curve – and helping prevent prices going negative.