Briefing Note | November 2021
Minimum demand and rooftop solar PV
An emerging but potentially critical threat to the reliability of the electricity system is the risk of minimum demand events. These have emerged because of the constant growth in rooftop solar PV system, leading to the increased likelihood of events when most of the electricity in a given jurisdiction is being supplied almost entirely from rooftop solar PV systems.
Minimum demand is a reliability threat for multiple reasons: mainly because rooftop solar PV is not controllable by the market operator and can increase or decrease output rapidly and because it does not provide critical supporting technical services required to keep the grid safe and stable.
The driver of this risk is the continued uptake of rooftop solar PV systems (now at 15GW across Australia). It is therefore a 21st century energy challenge that needs to be managed and solved.
The biggest risk appears to be during sunny, mild weekends and public holidays when demand is low but rooftop solar PV generation is high.
Some smaller, high solar PV grids (Perth and Adelaide) are already rapidly approaching critical minimum demand events.
The key technical risks under minimum demand conditions are voltage management, inertia, frequency control and system strength.
The solutions to these include retrofitting control devices on the inverters of rooftop solar systems, installation of technologies such as synchronous condensers (for inertia) and increased deploy of storage technologies (to help manage voltage and frequency).