16 Feb 2025

A new high‑water mark for suburban solar

New South Wales quietly set an energy milestone at 12 : 25 pm on Saturday, 15 February 2025, when rooftop solar systems met 60.3 percent of the state’s total electricity demand. The event—verified by AEMO’s high‑resolution SCADA feed—pushed coal output to its lowest midday level since records began in 1998 and forced spot prices into negative territory for nearly four consecutive hours. What makes the achievement remarkable is that it was delivered by hundreds of thousands of private rooftops rather than by a single utility‑scale solar farm.

How we reached 60 percent

New South Wales now hosts more than 2.95 million small‑scale PV systems totalling 9.1 GW of nameplate capacity. A cocktail of factors aligned to propel the fleet past the 60 percent threshold:

• High insolation: The Bureau of Meteorology measured solar exposure 8 percent above the ten‑year average for mid‑February.

• Mild temperatures: A cool southerly the night before kept air‑conditioning demand low.

• Expanded hosting capacity: Ausgrid and Essential Energy finished voltage‑management upgrades across 310 feeders, lifting export limits just in time for the sunny weekend.

• Smart inverter controls: Updated AS/NZS 4777.2 firmware allowed dynamic exports, preventing the blanket shutdowns once common on record days.

Coal’s midday nosedive

At the moment rooftop PV peaked, coal generators across NSW were down to 2.7 GW—barely 30 percent of their typical daytime output and the lowest midday dispatch in the state’s modern history. Several units at Eraring and Vales Point dipped to technical minimums; Bayswater’s Unit 2 opted for an early maintenance window rather than chase a negative AU $28/MWh price. For context, coal provided 75 percent of NSW generation at noon as recently as 2018; seven years later, the figure is 21 percent.

Price signals: cheaper power, but more volatility

Wholesale prices averaged minus AU $12/MWh between 10 am and 2 pm, rewarding retailers that pay households dynamic feed‑in tariffs pegged to spot prices. Yet the benefits cut both ways. As the sun dipped below western eaves at 5 pm, prices spiked to AU $438/MWh, illustrating the state’s growing “neck” of the solar duck curve. Batteries earned a tidy AU $426 per megawatt for a single cycle that day; gas peakers, however, ran only 27 minutes in total, drawing scrutiny over the viability of capacity contracts when running hours plunge.

Winners: homeowners, retailers, and batteries

Homeowners with rooftop PV harvested strong bill credits—those on Amber Electric’s wholesale pass‑through tariff earned AU $6 for the day just by exporting. Retailers offering “solar soak” plans saw uptake quadruple as dynamic‑tariff alerts pinged phone apps. Meanwhile, grid‑scale batteries like the 100 MW Wallgrove facility charged at a weighted average of minus AU $19/MWh and discharged at AU $403/MWh during the evening peak, recouping a full percent of capital cost in one Saturday.

Losers: coal generators and network planners

Coal units can technically ramp down to 40 percent of nameplate, but sustained negative pricing forces them to make tough choices: shut down and incur restart costs, or run at a loss hoping for evening spikes. Network planners face separate headaches: minimum load events stress protection schemes designed when coal was must‑run. They now scramble to re‑tune underfrequency load‑shedding and refine fast‑frequency response procurement to maintain stability when inertia sags.

Managing minimum demand: lessons learned

AEMO resorted to only 35 MW of rooftop curtailment—an 80 percent reduction compared with a similar record last year—thanks to flexible exports. The key interventions:

1. Dynamic voltage regulation: New on‑load tap‑changers at 110 kV substations lowered distribution voltages by up to 2.5 percent, expanding PV hosting headroom.

2. Six‑second fast‑frequency response: Battery bids filled 90 percent of contingency FCAS, slashing costs and freeing hydro units for energy dispatch.

3. Controllable hot‑water heaters: Over 50 000 smart relays turned on during the negative price window, soaking up 100 MW of otherwise spilled solar.

The rooftop fleet’s quiet evolution

Since 2022, every new inverter sold in Australia must be internet‑connected and compliant with its DNSP’s dynamic‑export API. As a result, 62 percent of NSW’s rooftop fleet can now throttle output in real time. Older inverters are catching up via retrofit dongles subsidised under the state’s Peak Demand Reduction Scheme—effectively turning what once was an unmanaged swarm of micro‑generators into a coordinated virtual power plant.

Implications for the coal exit timeline

Eraring’s four units are nominally scheduled to close by 2027, while Vales Point targets 2029. February’s record hints that economics, rather than timetables, may dictate earlier retirements. Origin Energy has already flagged intermittent off‑lines if negative‑price events exceed 1 000 hours per year—on current trends, 2025 could hit that mark. AEMO’s Draft 2024 ISP models the coal fleet dropping below 10 gigawatts nationally by mid‑2028—events like this lend weight to that aggressive scenario.

Policy response: more storage, smarter loads

The NSW Government fast‑tracked its fifth long‑duration storage auction in response to the record. Up to 600 MW/2 400 MWh of eight‑hour storage will be procured before winter 2026. On the demand side, newly mandated smart‑charger protocols come into effect July 1, forcing EV chargers above 7 kW to accept network signals. Combined with time‑varying export tariffs, these measures aim to flatten both the midday dip and the evening spike.

What could slow rooftop growth

Grid hosting saturation looms in Western Sydney and the North Coast, where some feeders now exceed 120 percent PV penetration at noon. Ausgrid warns that without accelerated deployment of community batteries and dynamic operating envelopes, it will cap new connections. A second risk is labour: the solar‑installer workforce migrated to large‑scale projects in 2024, leaving suburban rollouts short‑handed. Trade bodies want a new apprenticeship category for solar‑roofer‑electricians to stem the shortage.

Looking forward: the eighty‑percent test

AEMO’s most optimistic scenario has rooftop PV alone covering 80 percent of NSW demand on mild‑load spring days by 2028. Achieving that milestone will require:

• Another 3 GW of rooftop capacity (roughly 400 000 new systems).

• 4 GW of firming storage to stretch solar into evening peaks.

• Expanded dynamic‑export coverage reaching 90 percent of inverters.

• Successful commissioning of HumeLink and VNI West to move surplus into Victoria when NSW roofs saturate.

If February’s record taught grid planners anything, it is that suburban solar grows quietly until one day it remakes the entire midday supply stack. Coal has already felt the impact; next in line are peaking gas and slow‑footed retailers. The flip side is cheaper energy for households willing to match consumption to the sun—a preview of a future where many Australians live almost bill‑free, powered largely by their own rooftops.