Rooftop solar has been the runaway consumer success story of the decarbonising electricity market. More than 2.6 million households have stuck solar panels on their rooftops, with a combined capacity of more than 13,000 megawatts smeared across suburban Australia.
The rampant popularity of rooftop solar has also created major technical and equity problems. Solar PV households Home-owners) are subsidised by non-solar households (including renters and those in flats) in multiple ways: through federal government subsidies (via the deemed small technology certificates or STCs), through state feed-in tariffs and by paying less for networks (because these are mostly charged through consumption). Solar households get paid positive prices for their power, when the true value during the middle of the day is increasingly negative.
Australian consumers are often encouraged to oversize their solar systems, in part because the current regime of tariffs reward this. Big solar systems produce more electricity during the day than a household can consume, exporting that power into the grid. At low levels of solar PV this wasn’t a problem, but with 2.6 million systems, the amount of electricity being pumped back into the grid is greater than the grid can handle.
The most basic measure of this oversupply is rising voltage, particularly noticeable in high solar PV states like Queensland and South Australia, which can reach and surpass the safe upper limit of 258 volts. Voltage is like pressure in the electricity system. If too many solar systems are pushing electricity into narrow parts of the network, then voltages will rise above a safe level and eventually trip off the solar inverters (the box that connects the solar system to the grid).
Until recently, Australian households have had few disciplines put on their solar ambitions, leading many consumers to have a sense that they are entitled to build solar systems as large as they feel like. More recently networks providers have begun to impose constraints on new solar customers in parts of the grid, limiting or even preventing new systems where solar is already in oversupply. The alternative would be upgrading and increasing the capacity of the network, a cost borne by all customers but the benefits going only to solar households.
Governments have been loathe to act because solar is popular, particularly with retirees and with “working families” in the outer suburbs, which also tend to be marginal electorates. There are growing concerns that, left unchecked, continued solar expansion could even risk blackouts as voltage disturbances could trip off thousands of solar systems, shutting off their power supply.
It is into this politically sensitive debate that the Australian Energy Market Commission has now jumped: proposing changes to the market rules that would allow networks to impose charges on electricity exported from households at different times of the day. The idea is simple enough: the electricity grid could really use more electricity exported from households at certain times (like heatwaves, cold snaps and evening peaks, and less at others (mild sunny days at lunchtime when wholesale prices are plunging into negative value due to chronic oversupply).
Households are currently struggling to justify investing in a $15,000 battery to balance their solar systems, soaking up surplus power when its not worth much to be used at times when it is. The AEMC’s hope is that the rule change will help change the maths on this and result in a more balanced and stable distributed electricity system, rather than the all solar/few batteries system currently in play.
The proposal has drawn the ire of a handful of solar activists and the Victorian Government backed Victorian Energy Policy Centre, who claim solar households exporting electricity don’t increase network costs, conveniently ignoring the fact that increased network spending is the alternative solution to regulating distributed electricity investment, and one that would effectively subsidise solar households even further.
Rooftop solar PV is clearly a major part of the 21st century. It’s just going to require more parenting and more boundaries to keep the system safe and reliable.