December 2025 marked a pivotal month for solar energy generation in Australia’s National Electricity Market (NEM), with both utility-scale and rooftop solar achieving record outputs during the peak summer period.
Analysis of data sourced from Open Electricity (formerly OpenNEM) reveals not only the continued dominance of rooftop solar PV but also the growing contribution of utility-scale installations, alongside notable pricing volatility that underscores the challenges of integrating high levels of renewable energy into the grid.
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The month delivered a combined solar generation of 5,701GWh, representing a 9.36% increase from December 2024’s 5,213GWh. Favourable summer conditions, capacity expansions and improved system efficiencies drove this growth.
Utility-scale solar PV reached a record monthly output of 2,124GWh, a 13.8% year-over-year increase from December 2024’s 1,866GWh. Rooftop solar also set a new December record, generating 3,577GWh, a 6.87% increase from the previous year’s 3,347GWh.
When compared to November 2025, utility-scale solar generation increased by 17.03%, rising from 1,815GWh to 2,124GWh. Rooftop solar saw a slightly smaller month-on-month increase of 14.68%, growing from 3,119GWh to 3,577GWh.
This seasonal growth aligns with historical trends, as December typically represents the peak of Australia’s solar generation cycle due to high irradiance levels and extended daylight hours.
However, the data also reveals a widening gap between the two segments. Rooftop solar accounted for 62.7% of total solar output in December 2025, compared to utility-scale’s 37.3%, maintaining a 1.68:1 ratio that underscores the dominance of distributed generation in the NEM.
When viewed in the context of the broader 2025 generation data, December’s performance stands out as a continuation of the strong recovery observed since the winter trough in June.
Utility-scale solar generation increased by 106.5% from June 2025’s 1,028.4GWh to December 2025’s 2,124GWh, while rooftop solar grew by 147.4% over the same period, rising from 1,446GWh to 3,577GWh.
These growth rates are significantly higher than those observed during the same period in 2024, when utility-scale solar increased by 89.4% and rooftop solar grew by 139.1%.
Seasonal recovery and record-breaking growth
Daily generation patterns throughout December 2025 further illustrate the dynamics between the two segments.
Utility-scale solar output ranged from a low of 51GWh on 6 December to a peak of 87GWh on 9 December, reflecting a 70.6% spread.
Rooftop solar exhibited a similar range, with daily generation spanning from 93GWh on 16 December to 140GWh on 3 December, a 50.5% spread.
As seen in the graph above, the highest combined solar output occurred on 9 December, with utility-scale and rooftop solar collectively generating 222GWh.
This performance highlights the collaboration between the two segments under optimal weather conditions.
Conversely, the lowest combined output was recorded on 6 December, when utility-scale solar generated 51GWh and rooftop solar produced 98GWh, resulting in a total of 149GWh. This highlights the impact of weather patterns on solar performance, particularly during the summer months.
Pricing extremes and volatility: Challenges in Australia’s solar market
The pricing data for December 2025 reveals a complex and volatile market environment, with significant differences between utility-scale and rooftop solar.
Utility-scale solar prices ranged from -AU$9.43/MWh on 2 December to AU$231.45/MWh on 19 December, while rooftop solar prices spanned from -AU$54.76/MWh on 25 December to AU$477.16/MWh on the same day.
This disparity showcases the challenges of integrating distributed generation into the grid, as rooftop solar is more susceptible to negative pricing events due to its decentralised nature and limited ability to respond to grid constraints.
Negative pricing was a recurring theme throughout the month, with rooftop solar experiencing negative prices on 10 days compared to 6 days for utility-scale solar.
The most severe negative pricing occurred on 25 December, when rooftop solar prices dropped to -AU$54.76/MWh, reflecting oversupply and grid curtailment during periods of low demand.
Utility-scale solar, while less affected, also faced negative pricing on several occasions, with its lowest price of -AU$9.43/MWh recorded on 2 December.
Price spikes were another notable feature of December 2025, particularly on 19 December, when both segments reached their highest prices of the month. Utility-scale solar peaked at AU$231.45/MWh, while rooftop solar reached an unprecedented AU$477.16/MWh.
This convergence of high prices for both segments was driven by a combination of high demand and limited grid capacity during peak summer conditions.
The data also reveals that rooftop solar exhibited greater price volatility, with a total range of AU$531.92/MWh compared to utility-scale solar’s range of AU$240.88/MWh.
December 2025’s record-breaking solar generation and pricing trends underscore the transformative impact of renewable energy on Australia’s electricity market.
The OpenNEM data reveals not only the growing dominance of rooftop solar but also the increasing importance of utility-scale installations in meeting the country’s energy needs.
However, the accompanying pricing volatility highlights the need for continued investment in grid infrastructure and market reforms to support the integration of renewable energy.
You can explore previous solar generation performance in our NEM data spotlight series, with all entries available to PV Tech Premium subscribers.
