A new South Australia-based study has found that a number of solar households in the state’s capital are recurrently losing up to 20% of their solar generation due to network curtailment, and that many consumers have no idea the practice goes on.
The research shines fresh light onto the thorny issue of rooftop solar curtailment – the intentional reduction of power output from rooftop solar systems to the grid – and the fact that not all rooftop PV systems are created equal, in terms of the amount of excess generation they are permitted to export.
The Australian PV Institute study – conducted by a team at the UNSW with industry partners AGL, SA Power Networks and Solar Analytics as part of the RACE for 2030 project – investigated losses for 1000 PV and battery sites, and 500 PV-only sites in metropolitan Adelaide.
Analysis of the Solar Analytics data of 500 sites in Adelaide indicated that overall, the proportion of generation lost due to anti-islanding curtailment was very low, with an average of 0.35% generation being curtailed across all sites across all days.
A small proportion of sites, however, were found to be significantly impacted with the most impacted site experiencing around 20% curtailment over the entire 10-month period. Of all the other sites, a maximum of 10% curtailment was experienced, and the majority experienced negligible curtailment.
The proportion of days on which curtailment occurred due to anti-islanding was found to be relatively high, with 20% of sites experiencing curtailment on at least 21% of days over the 10-month period.
This suggests that while curtailment due to anti-islanding activation impacts a small proportion of overall generation, it does appear to occur frequently.
In terms of economics, the revenue losses from curtailment were found to be small for an average energy user, at less than $5 per year. But for those more heavily curtailed households were found to be missing out on around $40 a year, based on average tariff assumptions, with potential revenue loss also likely for VPP aggregators.
“The results indicate that average curtailment loss is less than 1% of the generation, and greater for PV-only sites,” said Baran Yildiz, the lead researcher of the Curtailment and Network Voltage Analysis Study (CANVAS), a RACE for 2030 project.
“However, a small number of households lost a lot more than the others, up to 20% of their generation, which clearly raises fairness concerns.”
The study identified a range of factors that resulted in higher levels of curtailment for some households compared to others, including the size, type, location, and age of the PV and/or battery system.
As RenewEconomt sister site One Step Off The Grid has reported, Australian network service providers have been progressively introducing solar export limits for years on their grids, and say it is needed as a way of heading off voltage stability problems in areas of high rooftop PV penetration.
A rooftop solar system’s grid export limit is determined by the local electricity network operator – sometimes on a case-by-case basis, sometimes according to an across-the-board standard, and typically at around 5kW.
But as more and more solar is installed on ageing grids designed and built to carry electricity one way only, networks are tightening their limits on solar exports and consumers are rapidly losing one of the key incentives for investing in the first place – feed-in tariff payments.
In Victoria, on certain solar-heavy parts of the state’s Powercor grid, solar industry insiders told One Step just over one year ago that as many as one in three installation jobs were having their solar exports either heavily restricted or limited to zero.
An obvious solution for households feeling the pinch of solar curtailment is to add battery storage and try to use up all of the solar produced on the rooftop, rather than send it to the grid.
Not everyone can afford to invest in batteries, though, and pressure is mounting on the energy industry to accommodate the the inevitable and unstoppable growth of rooftop solar on the grid, rather than impose increasingly harsh limitations on solar to make do with an outdated grid.
APVI reports that focus group participants in the CANVAS study, most of whom had not heard of curtailment, found the concept “off-putting” and questioned its fairness – both in light of the contributions rooftop solar have made to lowering electricity prices and in the context of the uneven nature of its impacts.
They also said that recognition of the positive role of distributed PV, and greater transparency about the practice of curtailment, were both required to help households make informed decisions about future investment in and management of their rooftop solar systems.
Possible ways forward included the need for consumer education campaigns, clear clauses in contracts, notifications about curtailment events, and household-scale modelling of the likely impacts of curtailment on electricity bills.
