How dynamic line ratings could boost wind generation by 50%

Wind power might be the cheapest source of renewable energy, but if it is curtailed due to grid congestions it won’t be as cost-effective as it should be.

This means an efficient network hosting capacity in Renewable Energy Zones (REZs) is critical for maximising transmission of wind energy to users. It also helps ensure a greater return – more MW per dollar – for renewable energy developers.

Transmission has traditionally relied on static line ratings (SLRs) – which have inflexible power-flow limits calculated according to least favourable weather conditions. One solution to congestion with SLRs is to expand or upgrade electrical infrastructure – a very expensive exercise.

Dynamic line ratings (DLRs), in contrast, aim to calculate the true capacity of lines by monitoring real weather conditions. They also take into account how wind energy can increase the capacity of distribution lines due to a cooling effect.

The question is to what extent DLRs could increase wind-hosting capacity in REZs in Australia?

In his paper, “On static vs. dynamic line ratings in renewable energy zones”, leading energy industry expert Professor Paul Simshauser examines the potential gains from DLRs for wind energy hosting capacity in REZs in Queensland.

Queensland’s unique and changing energy landscape

Simshauser says that on the demand side of the equation, Queensland has the highest uptake of rooftop solar PV in the world – at 44% of detached homes. This pattern has shifted grid-supplied maximum demand from the middle of the day to around 5pm.

On the supply side, the typical installation of the state’s REZs is a large wind farm. This has relevance to transmission line ratings, as wind production tends to dip in the middle of the day and peak outside of highest ambient temperatures.

When you combine these situations it means that grid demand is highest in the state when wind speeds are rising and having a cooling effect on thermal line ratings.

“Collectively, cooler temperatures and elevated wind speeds means the credible hosting capacity of wind generation within a REZ with dynamic line ratings may be substantially higher than static ratings suggest,” the paper says.

The changing landscape of Queensland’s energy prompts investigation into real-time transmission line ratings, according to Simshauser.

“Static and seasonal line ratings in Queensland reflected circumstances triggered by critical event maximum demand days – hot and still conditions during the middle of the day.”

However, the shift to renewable resources brings a different set of circumstances, and the presumptions of ‘hot, still conditions’ no longer seem relevant.

Model comparisons

In his research, Simshauser looked at four REZ models comprising a double-circuit 275kV transmission line – static, seasonal, and real-time dynamic line ratings, as well as DLRs with frequency controlled ancillary services (FCAS).

• Static line ratings – transfer capacity is limited to 1500MW all year long. The model finds optimal VRE hosting capacity to be 1700MW of wind, although this will only be reached periodically. The paper also points out how in this scenario, the two renewable technologies (wind and solar) compete for scarce REZ transfer capacity.
• Seasonal line ratings – static lines adjusted for seasons, which potentially results in wind capacity gains of approximately 200MW.
• Dynamic line ratings – capacity increases to around 2800MW, without any changes in infrastructure.
• DLRs with FCAS – this potentially produces additional gains in wind capacity of 400MW. However, the paper notes that this does not take into account the extra costs of an expanded FCAS suite.

Simshauser’s optimisation modelling suggests a shift from static to dynamic line ratings for a 275 kV REZ in Queensland can increase wind hosting capacity from approximately 1700MW to 2800MW. This is possible without the need to make substantial changes in the asset base.

The shift to DLRs could prevent the need for transmission line expansion or overbuilding – which is not only costly but can also encroach onto private land and risk disturbing sites of cultural or environmental significance.

The paper also refers to how DLRs with Frequency Control Ancillary Services could further increase hosting capacity. However, as Simshauser points out, this would involve extra costs and as such requires more research.

In conclusion, shifting from static to dynamic line ratings in renewable energy zones can increase wind hosting capacity by at least 50%. In turn this is likely to lead to better returns for renewable energy developers and investors

The full text of “On Static vs. Dynamic Line Ratings in Renewable Energy Zones” can be viewed here.