A Good Friday for reactive power

One of the likely consequences of a national lockdown to reduce the spread of COVID-19 is a sharp reduction in electricity demand. When most people stay home electricity demand falls. Falling electricity demand reduces reliability risk (running out of power) but may increase security risk at times of very low demand.

Minimum demand events have emerged as a new priority as we shift to more distributed generation, principally from rooftop solar PV systems. There are now more than 2.1 million Australian households with rooftop solar with a combined generation capacity of around 10,000 MW.

In aggregate this equates to a big and growing solar power station that cannot be controlled by the Australian Energy Market Operator (AEMO). It must be worked with.

Big rooftop solar generation is likely to be hardest to manage during times when electricity demand is very low. When the quantity of rooftop solar generation approaches the full load, it squeezes out other types of generation. There are technical challenges that need to be overcome if you want to run a pure rooftop solar generation system.

First you need to replace the large, spinning mass of a power station. The rotation of a large power station turbine creates inertia which is a critical ingredient in a stable electricity grid. It has the effect of slowing sudden changes in voltage and frequency which, if left unchecked, could trip the system off and cause blackouts.

In low demand conditions and high distributed generation there are also problems with rising voltages in the grid. AEMO is more frequently having to intervene to de-energise the grid by directing generators to do this job. It’s not sustainable as demand keeps falling and distributed generation keeps increasing.

High solar grids also risk having an undersupply of reactive power. Reactive power is the portion of electricity that helps establish and sustain the electric and magnetic fields required by alternating current equipment. Reactive power helps control voltages and overcome losses in transmission networks. Reactive power needs to be in balance.

Solar PV generators do not produce reactive power, because they are DC generators that use power electronics to convert this to an AC current.  So high solar PV operations need to be augmented by reactive power technologies like synchronous condensers and reactors. four new synchronous condensers are already planned for South Australia to help with system strength and other power quality issues that arise in high renewables generation there.

In 2019 AEMO identified the need for $72 million of reactive power support through the installation a network of reactors and synchronous condensers west of Melbourne. The plan was to have these technologies operational from 2021 to manage anticipated low demand events from that time onwards.

The emerging challenge is this Easter. Good Friday is often the lowest demand day of the year. This combined with a sustained lockdown in managing the COVID-19 outbreak may bring forward some of those challenging low demand conditions without the technology to manage them.

AEMO will look to direct generators to draw down voltage as they have done in the past. Fast changing circumstances create novel technical problems for an electricity system already operating at the leading edge of known experience.