AEMO data shows solar offloading falls 54% as battery capacity triples

Economic offloading of grid-scale solar in Australia's National Electricity Market (NEM), when solar farms choose to switch off because wholesale prices have fallen too far below zero, fell 54% (177 MW on average) in the September quarter from a year earlier, according to AEMO's latest Quarterly Energy Dynamics report. As a share of average solar availability, offloading plunged from more than 16% to 5.9%, RenewEconomy reports.

"This reduction reflected higher grid-scale battery charging and increased daytime operational demand, which reduced the need for grid-scale solar facilities to economically offload generation," AEMO said.

Standalone grid-scale battery storage capacity has grown three-fold in the past year, and the federal rebate has driven a surge in home batteries, creating new midday demand that soaks up surplus solar and keeps prices above zero more often. Most new solar projects are also being built with their own batteries connected behind the meter, and the first of these have started operating. Until now, solar farms without batteries had been forced to switch off, rather than pay someone to take their power, more than half the time at some sites.

State-by-state solar trends

Queensland saw the biggest change, while Victoria went the other way.

State	Change in Offloading	Volume Change
Queensland	-63%	down 139 MW, to an average 81 MW
New South Wales	-61%	down 37 MW
South Australia	-24%	down 7.5 MW
Victoria	+52%	up 7 MW

Wind generation offloading

Wind farms are less exposed to economic offloading because they produce most of their output outside daytime hours. AEMO says wind offloading fell in absolute terms to 266 MW. The share of available wind capacity subject to offloading held steady at 5.9% year-on-year.

South Australia recorded the largest decline, 35 MW or 31%. New South Wales saw the biggest percentage drop, with offloading falling 66% or 8.1 MW. Queensland wind offloading declined by 39%, a reduction of 8.6 MW. Conversely, Victoria experienced a 4.3% increase in wind offloading, adding 6.9 MW to the total.

Network curtailment rise

Network curtailment, imposed by local networks and the market operator because of bottlenecks, faults or security issues, went the other way: it doubled to a record average of 281 MW across wind and solar. Grid-scale solar was worst hit, with curtailment nearly tripling to 169 MW, or 6.7% of solar availability. The impact was felt most in southern NSW, where grid bottlenecks are more common, and in north Queensland. Wind curtailment across the main grid rose by about a third to 113 MW, or 2.5% of availability, with Victoria worst affected.

Background

Luminity reported on 23 October that, according to AEMO, grid-scale batteries now set the price in nearly half of all NEM intervals and, for the first time, supply significantly more power than gas in evening peaks. The same quarter saw grid-scale solar output rise 30% to a Q3-high average of 2,211 MW, and a record half-hour renewable penetration of 80.4% on 19 September.

What to watch

Whether battery charging keeps cutting offloading as spring and summer solar output climbs, and whether network curtailment, now the bigger constraint for NSW and Queensland solar farms, starts to ease. In South Australia, RenewEconomy notes that wind offloading may be eased by the new transmission link to NSW.