Kerry Burke is an associate analyst at Westpac Institutional Bank .

Victoria and South Australia have just finished a week which put the highest stress on the electricity grid since a similar heatwave occurred on 28^th-30^th January 2009. Despite the population of Victoria and South Australia increasing at least 7%² since then, the electricity demand supplied by the grid during the heat wave was just lower than the peak usage reached on the 29^th of Jan 2009.

Electricity demand from the grid in the recent heatwave peaked on Wednesday. There were initially warnings of potential load shedding¹ from the grid operator after the usually baseload Loy Yang A3 brown coal unit and one of the Torrens Island gas units tripped offline on Tuesday. However, demand came in slightly lower than forecast and apart from some minor local transmission outages, demand was fully supplied.

Speculation has already started on the effect of solar on electricity demand during the heat wave, with the Electricity Supply Association (ESAA)³ and the Australian Solar Council⁴ each producing different estimates of the amount solar contributed to reducing demand. Peak demand is an important driver of the cost of electricity as both the network and the generation fleet is sized to meet the largest credible demand forecast.

Producing estimates of solar energy production is difficult as the energy production occurs behind the meter that connects households and businesses to the grid. Some hope of making a good estimate exists due to the existence of PVOutput.org, a volunteer run site that lets solar system owners connect their inverters to the internet and automatically upload data on solar energy production. The site receives data every 10 minutes from hundreds of systems in each state. The data has been handily graphed on a real time basis at http://pv-map.apvi.org.au/ .

The solar owners using the site would be more enthusiastic about solar than the average owner and the data collected may overestimate energy production if the enthusiasts have higher efficiency systems. On the other hand, enthusiasts may be more likely to install solar even in poor locations, such as south facing or partially shaded roofs. Overall, PVOutput.org is the only estimate we currently have of real-time solar energy production.

The figures below show the 10-minute estimates of solar energy added back to the 5-minute metered electricity demand from Thursday to give the true native demand.  Not only did solar reduce the peak demand, it actually shifted the apparent time of maximum demand to much later in the day for South Australia.

The time shift in peak demand caused by solar makes the approach used by ESAA to measuring solar contribution lead to underestimations. It is not enough to look at when demand peaked and estimate solar production, as that fails to take into account that demand would have peaked earlier without solar.

If no solar had been installed, Victoria would have set a new demand record of 10,675MW at 1:55pm today 17^th-Jan-2014, higher than the metered demand of 10,572MW used at 12:35pm on the 29^th-Jan-2009. South Australia would have set a new demand record of 3,549MW at 4:30pm yesterday 16^th-Jan-2014, higher than the metered demand of 3,441MW set 4:25pm on the 29^th-Jan-2009. Solar reduced the maximum combined VIC & SA demand by 448MW.

Asking what happens when the sun doesn’t shine and the wind doesn’t blow ignores the spare capacity built into the grid to handle record demand days like yesterday and today. For the majority of the year, spare generation capacity can backup variations in solar or sudden failures at fossil fuel plants. Record demands, where there is little spare capacity, are caused by hot conditions and strong sunlight. Solar is now a critical component of the generation fleet that reliably supplies our power.

Kerry Burke is an employee of Westpac and a conjoint fellow at the University of Newcastle. Any views expressed do not necessarily reflect those of the Westpac Group.

1. http://www.aemo.com.au/News-and-Events/News/Media-Releases/Increased-Electricity-Demand-In-Victoria-And-South-Australia
2. ABS population data Jun-2013 (latest release) vs Dec-2008. http://www.abs.gov.au/AUSSTATS/[email protected]/DetailsPage/3101.0Jun%202013?OpenDocument
3. http://www.esaa.com.au/media/consumers_urged_to_conserve_power_as_heat_wave_peaks
4. http://www.businessspectator.com.au/news/2014/1/17/solar-energy/heatwave-states-should-thank-solar-owners, https://reneweconomy.wpengine.com/2014/solar-23763