Big sun a big headache in the Wild West

Perth sits at the centre of the world’s most isolated electricity grid, the south-west interconnected system. Out in the wild west, big sun is posing some serious challenges for the reliable operation of this lonely electricity island.

The new quarterly report by the Australian Energy Market Operator (AEMO) revealed that the Perth grid reported its lowest minimum demand event ever, at 11am on Saturday January 4 this year. Minimum demand fell to 1,135MW, breaking the previous record set three months earlier.

The reason for this record low point in demand, and therefore electricity generation, is rooftop solar PV. January 4 was a sleepy, sunny and mild Saturday morning in the world’s biggest mining town. demand was low and the sun was bright. AEMO estimate that 44 per cent of total demand was being supplied by more than 300,000 solar systems spread across the Perth suburbs.

This is good news for reduced electricity emissions but not so good for grid operators. Rooftop solar PV has become a giant, uncontrolled solar power station. It has been installed without any way of being regulated or turned off. And being solar generation, it powers up when the sun shines and down when its dark or cloudy.

As rooftop solar generation continues to grow it increases the size of this uncontrolled wave of generation. Solar is an inverter based source of generation, meaning it supplies energy but not all the other suite of supporting technical services needed by a grid: frequency services, system strength and inertia.

These historically have been provided by large power stations with big rotating turbines, but as rooftop solar continues to expand, there won’t be any power stations on to supply these. In the case of Perth, there is no other grid around to plug into for help.

This is solvable: batteries have proven to be adept at supplying frequency, and large flywheels called synchronous condensers can be installed to supply inertia.

The really big problem caused by large surging rooftop solar is its impact on Perth’s remaining coal fired power stations: Muja, Collie and Bluewaters 1 and 2. Together they have a capacity of 1,860MW, and continue to play a critical role in Perth’s electricity supply. They are particularly critical in helping to supply enough electricity for Perth’s maximum demand peaks, which reach around 4000MW on very hot days and are increasing.

Coal generators are not designed to switch off and on. As big solar takes over more of the region’s electricity supply on mild sunny days, it forces the coal generators to switch down and eventually off. Being forced off and on by renewables is an early death for coal generators. It was what caused South Australia’s Northern Power station to close a decade ahead of its expected shelf life.

Early retirement for Perth’s coal fired power stations (Muja and Collie are government owned, Bluewaters is private) will cost the WA Government billions in replacement capacity. It would be cheaper, but politically unpopular, to slow rooftop solar PV installations, or mandate they be fitted with greater controls.

With the critical levels of solar possible by 2025, the WA Government is running an Energy Transformation Strategy to try and manage the fine line between politics and cost. Meanwhile minimum demand keeps growing and the clock keeps ticking.