It should be noted that high penetration of rooftop solar strongly impacts the current flow through the distribution network. A traditional network predominantly involved unidirectional power current with power supply from central power stations down to consumers below. Additionally, with more energy produced compared to consumption at domestic setups, the extra energy is injected from the MV and LV networks, inducing reversal of the current from the desired direction to the opposite direction. This reversal often results in voltage rise at the point of supply since the network infrastructure, comprising transformer and voltage regulators, could not possibly supply thousands of small power stations to counter the extra energy produced through solar energy at domestic setups. This is more visible in areas where the use of solar energy and solar generation at peak hours of the day is high, like South Australia, Queensland, and some areas within New South Wales.

The midday over-supply can cause curtailment, which involves the intentional reduction of solar energy contribution to regulate voltages within the required levels for operation. The curtailment ensures that overvoltage does not exist, but sometimes, it can be a contributor to wasted renewable energy as well as reduced income for consumers, thereby generating economic factors for both the consumer and the distribution networks. The medium voltage level, denoted by voltages between 11 kV and 33 kV, has its special challenges due to the two-way flow, which can be counterproductive when using former protection systems and/or former voltage regulation systems, as the on-load tap changers (OLTCs) can fail to react correctly to the sudden transients due to solar energy intermittency, sometimes overcorrecting or even failing to do so for voltage correction.

Smart Inverters and Advanced Device-Level Solutions

Modern solutions for managing these challenges combine device-level actions with network-wide operational strategies. Smart inverters, which are now standard on most new PV installations, actively support the grid: through functions such as volt-var control, inverters can inject or absorb reactive power to help regulate local voltages. Volt-watt control enables them to reduce active power output when voltage levels exceed thresholds. Frequency-responsive functions may further contribute to overall grid stability. All these inverter capabilities allow distributed solar generation to become an active participant in maintaining voltage stability, not a passive source of potential problems.

Besides the implementation of smart inverters, OLTCs and voltage regulators in substations are also being upgraded to be able to handle the dynamics of distribution energy resources (DERs). More advanced methods of tap operation are being applied to make optimal use of primary and real-time information about DER forecasts to limit unnecessary mechanical switching and to preserve feeder voltages within specified ranges. A tiered system involving coordination of inverter operations and OLTC controls offers a multi-level solution to the challenging situation created by high penetrations of DERs.

Coordinated Network Management with DERMS

The deployment of Distributed Energy Resource Management Systems (DERMS) has come into play as an important mechanism in managing DERs. DERMS integrates, monitors, and controls PV, battery storage, and other flexible loads to anticipate voltage control and oversupply. The DERMS software forecasts PV output based on weather conditions and past behavior and uses either storage resources or inverters to control voltage breaches. Policies in Australia, titled the Open Energy Networks project, which includes the Australian Energy Market Operator (AEMO) and different distribution networks, aim to manage DER effectively to optimize networks without investing in infrastructure. There seems to be a move from viewing rooftop solar as an issue to viewing it as an asset that can be managed.

The Role of Energy Storage

An important role in the management of oversupply for both back of the meter and grid-level energy storage, respectively, is played by the integration of energy storage technology. The excess supplied electricity from solar plants is fed into household batteries, which then supply electricity back into the networks during the evening peaks, thus preventing back power flows and improving voltage support. While the community batteries help implement self-consumption and as such prevent oversupply and ensure the economic feasibility of rooftop solar PV plants, the larger scale grid-level storage plants, as demonstrated in the Hornsdale Power Reserve in South Australia, the Big Battery in the state of Victoria, and the ESCRI project in the state of New South Wales, play an important role in managing oversupply by offering grid support services like frequency and energy balancing, and voltage support.

Virtual Power Plants and Demand Response

Virtual Power Plants (VPPs) further enhance the concept of coordination between DERs in that VPPs involve the integration of tens of thousands of residential-size solar PVs, energy storages, and flexible loads that can be operated remotely and in a collective manner. VPPs can supply energy in a collective manner for maintaining the stability of the voltage, for load balancing in the distribution feeders, and for market participation. Incentives in the state of New South Wales encourage residential participation in VPPs so that residential energy can be provided in a collective manner for offering services to the grid during situations of oversupply. Similarly, demand response also employs flexible loads like air conditioning units, hot water heaters, and pool pumps that can absorb excess energy during situations of high solar irradiation.

Forecasting, Analytics, and Predictive Control

Forecasting and prediction analysis are also increasingly incorporated into the management of DER. This is because a reliable prediction of PV and load profiles enables network managers to design proactive plans and control measures to counterreact to voltage excursions when they occur instead of after the events occur. It is evident that through the use of controlling systems and management with the help of energy storage management and smart inverters, Australian networks can match the voltage profiles and ensure stable network function even when the networks experience high DER penetration.

Australian Case Studies

Australian case studies provide insight into the efficiency of these approaches when applied to real-life networks as well. “Networks Renewed” is an example of collaborative efforts between the University of Technology Sydney, the energy company Essential Energy, and the energy distributor AusNet Services, where the project successfully proved that solar PV and batteries could dynamically control network voltage and enhance network reliability as well. Participation of voluntary consumers with smart inverters and batteries helped the project prove the efficiency of DER networks and how they could help with voltage stability and postpone necessary and costly network reinforcement at the same time. Regional projects like the “Smart Sun Pilot” project developed in Western Australia successfully coordinated the operation of different DER to control low voltage issues at the network level and proved the efficiency of small-scale coordination between various network participants.