Australia has one of the most ambitious renewable energy development pipelines in the world. However, getting a project built is only part of the challenge. It also needs to connect successfully to an increasingly complex power system.

Rennie Executive Director Matt Rennie recently sat down with Ajith Tennakoon, a senior engineer in Rennie’s Grid Connections team, to discuss what actually makes connection difficult, what developers can do about it, and what happens when Australia adds another layer of complexity through very large new loads such as data centres.

Ajith has more than 30 years of power-system engineering experience across generation, transmission, protection and grid connection. He began his career with the Ceylon Electricity Board, working in power station operations and control before moving into transmission and ultimately heading transmission network protection. Ajith is a Chartered Professional Engineer with Engineers Australia and co-author of the engineering textbook Protection of Modern Power Systems.

Since moving to Australia, he has specialised in grid connection studies for renewable generation and storage. We asked him what he has learned.

Matt Rennie: What are the main things that make an Australian connection application difficult?

Ajith Tennakoon: One of the most important areas is the inverter model. Wind, solar and battery projects are increasingly inverter-based resources. The inverter and its control system determine how the plant responds electrically to changes and disturbances in the power system. The models we use in connection studies are effectively our representation of that behaviour.

Australia presents some particularly challenging conditions because renewable projects are often located a considerable distance from the stronger parts of the transmission system. Long transmission lines increase network impedance and, in some locations, result in relatively low short-circuit ratios.

In practical terms, that means the electrical conditions at the connection point can be more sensitive to changes in generation and network conditions.

We therefore undertake detailed studies to understand how the plant will perform across a range of operating conditions and disturbances. Those studies can identify areas where the model or controls can be further optimised. We then work closely with the OEM to refine the model and repeat the relevant studies.

That iterative process is an important part of demonstrating that the plant will perform appropriately within the Australian power system.

Matt: Does that mean grid connection should be considered when a developer is selecting its OEM?

Ajith: Definitely. Developers should consider the connection process as part of the technology selection rather than treating it as something that happens afterwards.

This is not about saying one inverter is good and another is bad. Different OEMs have different levels of experience with Australian network conditions, and that experience can be valuable.

An OEM that has completed a number of Australian connections may already have models that have been tested across a range of local conditions. Its engineering team will also generally understand the information that AEMO, the NSP and the connection consultant are likely to require.

Technical support is equally important. During a study we may identify a question that requires input from the OEM before we can proceed. The speed with which that issue is understood and resolved can have a direct effect on the project schedule.

For a developer, the capability behind the equipment therefore matters alongside the equipment itself. Model maturity, Australian experience and access to responsive technical support can all influence connection cost, timing and risk.

Matt: Who is actually involved in getting a project connected?

Ajith: The connection engineer is effectively working in the middle of an ecosystem.

The key parties are normally the developer, the OEM, the network service provider and, through the process, AEMO.

At the beginning of an engagement, we typically prepare separate requests for information for the developer, OEM and NSP. We need different technical information from each party before we can undertake the studies properly.

Once the studies begin, the process becomes iterative. We may identify a question for the network or require additional information from the OEM. The network may review a submission and request further analysis. A model may be updated and particular studies may need to be rerun.

One of the things developers sometimes underestimate is that the network is also managing a substantial pipeline of connection applications.

If an NSP begins reviewing your project and then needs additional information, there can be consequences if the response takes a long time. Those network engineers have other projects to assess and may need to move their resources elsewhere. It does not necessarily mean the same people can immediately return to your project when the information arrives.

Managing those interfaces well is a very important part of achieving an efficient connection.

Matt: How long should a connection application take?

Ajith: If the necessary information is available, the models perform as expected and there are no significant technical issues, the consultant’s initial application work can potentially be completed in around four to six months.

The complete process through to 5.3.4A can take considerably longer. A year is not unusual, and some projects can take longer again depending on their complexity and the issues that arise.

It is important to understand that this is not one engineering study followed by an approval. There are multiple studies, reviews and interactions between different organisations.

There are also differences between networks and whether the plant type is solar, wind, hybrid with a BESS, DC coupled, AC coupled, grid-forming, grid-following etc.

The National Electricity Rules provide the overall framework, but individual NSPs have their own technical guidelines and assessment processes. Powerlink, for example, has a staged approach to the 5.3.4A submission process in Queensland. NSPs can also have different requirements for areas such as harmonic studies.

A connection engineer needs to understand both the national framework and the practical requirements of the particular network.

Matt: Looking further ahead, what worries you most about the Australian grid?

Ajith: The scale of the change.

We are progressively retiring large synchronous generators while connecting renewable generation in different locations across the network. That changes both power flows and the technical characteristics of the power system.

There are network capacity constraints that will require augmentation, but there are also system-strength and stability considerations.

Traditional synchronous generation inherently contributes characteristics such as inertia and fault current. Inverter-based resources behave differently. We are seeing significant advances in technologies such as grid-forming batteries, syncons which can provide important system-support capabilities, but the overall system still needs to be carefully engineered as the generation mix changes.

We therefore cannot think only about how many gigawatts of renewable generation Australia needs. We also need to consider where that generation connects, how power moves through the transmission system and what services are required to maintain a secure and stable power system.

Matt: Now put data centres into that picture. What happens when somebody wants to connect, say, an 800 MW data centre?

Ajith: This is where the problem becomes particularly interesting.

An 800 MW data centre is an enormous load. You cannot simply look at the site and ask whether there is an 800 MW connection available.

The first question is obviously where and how the load can connect. However, you also need to ask where the electricity is going to come from.

The generation supporting that load may be located hundreds of kilometres away. It may involve a portfolio of wind, solar, battery storage and potentially other sources of firming. Those generation assets themselves need grid connections, and their output needs to move through the transmission system to the load indirectly.

You therefore need to understand what happens to the network when you add the load, what happens when you add the generation required to support it, and what happens under different operating and contingency conditions.

From a power-system perspective, you cannot solve each component independently.

You need to consider the load, the generation and the grid together.

Matt: That starts to become more than a grid connection problem, doesn’t it?

Ajith: Yes. It becomes an integrated energy problem.

The client needs to determine how much power it requires, where it should connect, where the generation will come from, what storage or firming may be required and how the network will accommodate those arrangements.

There are then commercial questions about how the electricity is procured or contracted, regulatory questions, network questions and detailed engineering questions.

Those decisions interact.

For example, the technically easiest place to connect a load may not necessarily produce the best commercial power solution. Similarly, a generation portfolio that looks attractive commercially may create network constraints that change the overall economics.

The engineering and commercial work therefore need to inform each other from an early stage.

Matt: How important is the experience of the principal engineer leading the work?

Ajith: It is extremely important because grid connection requires both technical depth and continuity.

The principal engineer needs to understand the power system, the plant controls and the modelling, but also the history of the project.

After six or nine months on a connection, an experienced engineer understands why particular decisions were made, what has previously been discussed with the NSP, what issues have arisen with the model and what the OEM has done in response.

If that engineer changes, even with a good handover, the incoming engineer needs time to develop that understanding. These are complex projects. You cannot simply read a file and immediately acquire all of the technical history and judgement that has developed over many months.

Communication with the developer is also critical.

Developers are managing financing, equipment procurement, planning, construction programmes and commercial commitments. They need to understand what is happening in the connection process, why a particular issue matters and what needs to happen to resolve it.

A good grid engineer should be able to explain those issues clearly, not simply produce technically correct studies.