Go West, Southwest that is


David Leitch


May 6, 2024

Following the path of least resistance

Whether its Kurt Lewin’s Forcefield theory, or electicity flowing, or water flowing generally the action moves to the area of least resistance.

In the Central West support for renewable energy seems lack lustre.

In New England, perhaps better called Very Old England where the National party hosts some of the most rabid anti renewable people outside of QLD, any kind of development seems to meet stiff resistance. No matter the hosipitals are inadquate, airfares are sky high, crime is rampant. The region comes across as against economic development. And that’s despite the fact there were just as many supporters as opponents of the Winterbourne wind farm.

So developers look to where the going is easier and where they are more likely to be welcomed.

In the Soutwest the economic opportunity appears to be better received. This was brought home by the lack of objection to the Delta/Yanco wind farm, 1500 MW and now sold to Origin Energy for potentially up to $300 m($0.2m/MW).

The South West REZ and Victoria’s V2 REZ are in the transmission junction

My hat goes off to Spark Renewables who a few years ago were amongst the first to see the potential of the SW REZ.

The West of Wagga and around Kerang in Victoria has tremdous potential to be the main hub for electricity production South of Queensland. This area has three main attractions:

  • It has access to Project Energy Connect from South Australia, to Humelink and to VNI West
  • The wind resource, particularly in NSW is adequate, 7 M/S or better at 100 metre hub height
  • At the moment there is good community acceptance. And why wouldn’t there be.
Figure 1: SW REZ and V2 wind speeds. Source:www.renewmap.com.au

Its important to understand that the power and energy from this area can go to Victoria, or less likely South Australia as well as to NSW depending on conditions. Why build all this offshore wind in Victoria when you have this fantastic much cheaper resource to the North? All that is required is enough transmission?

Ignoring transmission constraints and the related marginal loss factors the over 15 GW of wind plus say 3 GW of solar, representing projects presently under development could produce say 40 TWh or that is 40% of the combined 2023 NSW & Victorian operational consumption, 20% of NEM wide operational consumption.

Clearly developers worked this out long ago. I’m so slow. Not just any developers either. The following table shows projects under development in those two zones over 500 MW.

Figure 2: Big projects in SW/V2. Source: www.renewmap.com.au

Spark, Vriya/ORG, RES, Engie and Goldwind have over 11 GW of projects combined. These are significant developers with money and credibility. Not that most of the others in the above figure don’t, this REZ is littered with what in the tennis world one might term contenders.

DC lines are more relevant with REZs than without REZs

By and large, AEMO, Transgrid, Powerlink have argued for AC connections over DC. There are probably a number of reasons for this, but one of them has been that most of the cost in a DC transmission line is the large, expensive and noisy converter stations at each end. The need for a conversion station means that DC is a point to point system, it doesn’t generally allow for random generators to connect along the way.

A second disadvantage is that the circuit breakers for very high capacity DC lines are not that available, at least that is what I read. And underground DC lines are hard to repair. Admittedly older style and under water but we have all seen how long it took to repair a problem with Basslink. Tasmania lost the connection for months.

Still I am not the person to talk about the technical side of things. What I can say is that:

  • Most future renewable generation will be built in REZs
  • New transmission is largely being built to carry power from REZs to load.

Consequently, few new generators will be built outside of the REZs and hence there is no need to have the interconnection capacity along the way. To that extent the argument that AC lines are a better choice than DC lines is less valid than before REZs came along.

A financial analyst’s concept of transmission capacity

Google is of only limited assistance in understanding transmission capacity. Not only that, the questions, ie how much power can a 500 KV line carry may remain the same but the answers slowly change.

The best “old school” answer I could find was from the Baylor University website AEP_Transmission_facts

What I read is that AC transmission power capacity increases with voltage. More volts more power. However AC transmission is limited by heat, by reactive power impacts caused by its capacitance and inductance and AC transmission also has a “skin effect” which means that only the outer part of the cable carries power. The longer the cable the greater some of these effects. As discussed in prior article new conductor materials can increase the capacity of AC transmission

Transmission lines also have a number of circuits. Typically, at least in Australia, either 1 or 2. Generally the maximum permitted power capacity on a transmission line is calculated with reference to allow for a “circuit or line loss” over at least part of the transmission line length.

The upside to this calculation is that as the number of circuits increases the maximum amount of power that can be carried goes up more. So 4 circuits can carry more than 2X the power of 2 circuits. AEP explains SIL of 1 as

a loading level at which the line attains self-sufficiency in reactive power.

Using the SIL concept, three 500 kV or six 345 kV circuits would be required to achieve the loadability of a single 765 kV line. Specifically, a 765 kV line can reliably transmit 2200-2400 MW (i.e., 1.0 SIL) for distances up to 300 miles, whereas the similarly situated 500 kV and 345 kV lines with bundled conductors can deliver only about 900 MW and 400 MW, respectively. For short distances, these relationships can differ to some extent reflecting thermal capacities established primarily by the number/size of line conductors and station equipment ratings.

Alternatively a 500 KV line can carry 1500 MW for 225 km assuming both ends of the line are “well developed”.

An example of combination overhead AC and DC line is SunZia connecting wind in New Mexico to Arizona originally conceived as twin circuit AC its now effectively a DC and parallel AC line with combined capacity over 4 GW.

Worldwide the AC transmission votage record is apparently the Ekbastuz-Kokshetau 1150 kV, 432 km line which can carry 5.5 GW on 45 metre transmission towers. There are a dozen existing AC and DC lines in China that carry 5 GW or more, typically at 800 kV - 1000 kV and sometimes double circuits.