An innovative trial in South Australia to test alternatives to imposing a “sun tax” on rooftop solar sent to the grid has been given another year to run after landing a new short-term waiver from ring-fencing rules.
The groundbreaking Market Active Solar trial, or MAS, is testing how to pay people for curtailing their solar exports, and see what happens when inverters must handle instructions from both the network operator and a retailer.
The latest ring-fencing waiver from the Australian Energy Regulator (AER) will allow SA Power Networks (SAPN) and Engie to keep testing the concept with 100 customers until the end of December 2026.
The trial builds on South Australia’s nation-leading efforts to manage the oversupply of rooftop solar during the middle of sunny days when high levels of generation clash with low – and sometimes negative – demand.
It’s testing what happens when SAPN receives a signal from a retailer wanting to curtail solar exports and blends this signal with its own flexible export limit to then publish on the customer’s inverter.
Early on, the focus had been on testing and fine-tuning at a network level alongside inverter companies Fronius, SMA, and SolarEdge, and energy management software company SwitchDin.
Then came the test for how it could work with retailers, with Engie and AGL participating in the latest trial and paying customers for curtailing their exports.
Does it work?
Engie went into the trial theorising it might be able to save as much as $9000 per megawatt (MW) of curtailed rooftop solar when wholesale market prices hit negative $100/MW.
What it found was the saving was closer to $7,000/MW.
The participating ENGIE customers are paid $10 a month in compensation for what they would’ve earned in feed-in-tariffs from exporting excess solar, as well as a $100 sign up credit and $50 from doing a survey at the end.
While Engie identified some technical challenges – some 12 per cent of sites had an issue that meant the curtailment signals weren’t going through – one key obstacle on the customer side is communication.
Given retailers will be paying customers a fee for how much power they don’t export, finding ways to transparently tell them how much power they would have generated in the curtailment period will be one of the next hurdles to cross.
AGL found that sites with multiple inverters, batteries, or high loads didn’t respond as well to the five-minute instructions as simpler sites, and instructions may not be acted on instantaneously by local inverters either.
Possible thanks to market-leading flex
The waiver gives the trial a bit more runway for the AER to look at what worked and what didn’t.
“Through the MAS trial, SAPN is exploring new approaches to increase the value from renewable energy, while improving utilisation of network assets (the FELs data and control systems, in this case),” the AER said in its decision.
“The AER considers that continuation of the trial will allow SAPN to gather further insights on customer participation, design solar management strategies that lead to efficient integration of solar generation into the grid and generate learnings that may inform the long-term purpose of the MAS trial activities.”
This type of trial is possible in South Australia thanks to SAPN’s shift to smart solar exports.
On July 1, 2023, new rules made it mandatory for all new or upgraded solar systems to be technically compatible with flexible export limits of up to 10kW.
Households that opt in to flexible exports are, most of the time, allowed to export the maximum amount the network and their inverter can handle, up to 10kW per phase.
Those households that opt out of flexible exports are limited to a set 1.5kW per phase export limit.
During an October update on the MAS trial progress, SAPN said about 90 per cent of customers are choosing the flexible option and it has 138.4 megawatts of curtailable rooftop solar now under its control.
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