Innovative technology to enable more solar exports

Energy Queensland and its subsidiary distribution utilities, Ergon Energy Network and Energex, are deploying a new technology to improve customer power quality and enable increased solar exports to the grid. Low voltage statcoms are being utilised to manage power quality and improve voltage regulation for customers on the 230V network.

As one of the world’s hotspots for rooftop solar photovoltaic (PV) systems, Queensland’s electricity network has seen a fundamental shift in how customers interact with the grid. With more than 500,000 solar PV systems installed throughout Queensland, two-way power flows are a common occurrence on the low voltage (LV) and medium voltage (MV) network (i.e. the 11kV, 22kV and 33kV network), as customers look to sell their excess generation.

This two-way transfer of power creates challenges for the grid that has historically been designed for one-way power transfer.

Electricity grids of the early- and mid-20th century were designed to deliver power from centralised generators to end-use customers.

The main challenge they faced was meeting maximum customer demand. However, the changing customer interactions of the late-20th and early-21st centuries have seen this paradigm begin to shift. Electricity grids are becoming more interactive, as customers invest in their own generation and utilise technologies like energy storage and home energy management systems to more actively
manage their energy needs.

Although maximum demand is still a concern for utilities, the evolving conundrum requires solutions that can manage a more diverse and rapidly changing set of network conditions. The grid of the 21st century must be capable of meeting periods of high load, low load and reverse power flow cost effectively.

Statcom units in place

Arriving at statcoms as the ‘right’ solution

Ergon Energy Network’s move to add LV statcoms to its arsenal of network solutions is an example of how it is working to address this issue with solutions that are innovative, cost effective and flexible. The decision to deploy LV statcoms as an additional network management tool is the culmination of pilot and trial projects that demonstrated the benefit LV statcoms can provide.

Statcom is a concatenation of STATic synchronous COMpensator. Statcoms are voltage source converting power electronic devices, similar in nature to solar PV inverters. They help to regulate voltage by drawing or injecting reactive power from the grid by generating a current that leads or lags the network voltage.

In 2013, Ergon Energy Network first investigated the application of statcoms in its distribution network. This pilot assessed MV- and LV-scale devices to assess their ability in managing network voltage.

Following the promising findings of this pilot, Ergon Energy Network conducted a market scan, trialling a number of different LV statcoms as a part of the Urban LV Statcom Project based in Townsville. This project assessed a range of different characteristics about these statcoms, including their affordability, reliability, ease of use and performance.

The success of this trial saw Ergon Energy Network proceed to tender in 2017 for the supply of LV statcoms, and ultimately sign with Brisbane-based business Statcom Solutions. Ergon Energy is now in the midst of deploying this technology as another tool to manage low voltage networks.

Mick Bellero (left foreground, Technical Lines Person in Mossman) and Anthony Torrisi (right background, Technical Officer in Cairns) install statcom equipment at Mossman

Statcoms, power quality and solar PV

Statcoms have traditionally been utilised in transmission networks and areas with high reactive power transfers. In these applications, large-scale statcoms provide power factor correction and voltage support within the transmission network. Ergon Energy Network’s move to utilise statcoms in its LV distribution network leverages the same technology and principles at a smaller scale.

In doing so, Ergon Energy Network is drawing upon a diverse range of solutions to build a flexible network that is equipped to meet changing customer needs.

To date, the use of LV statcoms within Ergon Energy Network’s grid has been targeted at overhead three-phase distribution network with high levels of rooftop solar PV penetration and large evening loads. The impedance characteristic of overhead three-phase networks lends them to voltage regulation through reactive power management, known as Volt-VAR regulation.

To deal with the traditional challenge of peak demand, during which the network can experience low voltage issues, the LV statcoms supply reactive power to the network and boost the voltage. This has the added benefit of providing a localised supply of reactive power for customer loads that tend to consume varying levels of reactive power.

However, one of the advantages of LV statcoms is that they provide a means for managing the prevailing challenge presented by rooftop solar PV – voltage rise resulting from reverse power flow. During periods of light loading and high solar PV generation, reverse power flow can cause LV network voltage to rise. If the ten minute average voltage at the point of connection of the solar PV inverter rises above 255V (for a single phase unit), AS 4777.2:2015 requires that the inverter disconnect, stopping generation from the solar PV system.

During periods of high network voltage that correlate with high solar PV output, LV statcoms help to reduce the network voltage by drawing reactive power from the grid. As a result, the benefit for solar PV systems and customers alike is two-fold:

1. Lower voltage during periods of high solar PV generation makes it less likely these systems will disconnect, maximising the output from existing solar PV systems
2. Better voltage regulation helps to remove constraints that may otherwise limit additional solar PV systems from connecting to the grid, while limiting the potential for damage to customers’ appliances due to under or over voltages

In May, Ergon Energy Network completed its first LV statcom installation in Mossman, North Queensland.

Although the systems are yet to experience the height of summer solar PV generation, they have already proven their worth by:

1. Maintaining the localised grid voltage at levels that have not caused customer solar PV systems to trip
2. Allowing additional voltage “headroom” for PV exports
3. Improving the overall voltage regulation and power quality for customers supplied from the local network

As summer approaches, the LV statcoms will help to minimise solar PV disconnections, and provide a detailed understanding of the performance of the LV network via their remote monitoring capability.

Over the coming months, Energy Queensland will be working to finalise the deployment of LV statcoms within its two utility networks and look to utilise them as an additional tool in managing network constraints. Future installations are currently planned for Wycarbah (near Rockhampton), Hervey Bay and Brisbane.