Large scale wind and solar farms in South Australia are being affected by two new network constraints revealed over the past week, adding to the growing amount of problems affecting the sector.
The new constraints affect the two main links from South Australia to Victoria, one because of network equipment failure that could last another 12 months, and the other the result of growing concerns about the stability of the grid in north-west Victoria.
The biggest constraint is being imposed on the Heywood inter-connector, where flows from South Australia to Victoria are being restricted from 650MW to 420MW as a result of the failure in July of a “static VAR compensator” (SVC) at Para in South Australia, which is not expected to return to service until mid-2021.
The other restriction was imposed on Thursday on the MurrayLink HVDC connection to the north, where flows from South Australia to Victoria are being restricted from 220MW to 95MW by the Australian Energy Market Operator because “new technical issues impacting grid performance and operational stability have been identified”.
The West Murray region has been highly problematic, with concerns about system strength and voltage problems resulting in the halving of output from five big solar farms for more than seven months, warnings of “material” constraints in south-west NSW due to grid congestion, and other constraints in what has become known as the “rhombus of regret” in Victoria, referring to the shape of the network in that region.
The MurrayLink constraint could be in place until mid-October while AEMO seeks potential solutions, and many wind and solar farms in South Australia may find their output constrained, or forced to switch off altogether, when normally they might expect to be able to export surplus capacity to the neighbouring state.
This occurred this weekend, when at least eight wind farms and one large scale solar farm in South Australia had their output cut to zero at various times on Saturday – despite the windy conditions – because of near record low demand in their own state and the new export limits, which caused negative prices over much of the last two days.
Some wind or solar facilities will always switch off when prices are negative, but others were obliged to do so because there was simply no way to export the surplus power. Among those reduced to zero output were all three Lake Bonney wind farms, all three Snowtown wind farms, the Mt Millar, Lincoln Gap and Cathedral Rock wind farms, and the Tailem Bend solar farm.
The issue was further complicated by relatively low demand and low prices in Victoria, and relatively low demand across the main grid which contributed to bottlenecks in the links between Victoria and NSW and Tasmania, and between Queensland and NSW.
Paul McArdle, from Global Roam, the providers of the popular NEM-Watch widget, estimates that at the high point (or low point) on Saturday afternoon, more than 2,000MW of semi-scheduled wind and solar farms were curtailed across the main grid. That does not include smaller non-scheduled facilities.
That’s a shame, because if those wind and solar farms had not been curtailed, it would have meant that well over 50 per cent of the country’s main grid was being supplied by renewables, perhaps more than 50 per cent by wind and solar alone, which would have set a new record.
The three big batteries in South Australia (and to a lesser extent the two in Victoria) spent as much time as they could charging at negative prices, but the situation calls for both more storage – both household and grid scale battery and pumped hydro (if that can be made to work financially), and the construction of a new link to NSW called Project EnergyConnect.
In South Australia, the situation is even further complicated by the growing amount of rooftop solar and its growing share of the generation mix, which is pushing “minimum” demand to levels that AEMO says will be hard to control.
On Saturday, see graph above at 1pm (courtesy of OpenNEM), when rooftop solar was providing 60 per cent of local demand, leaving little room for large scale wind and solar. Minimum grid demand (what’s left after rooftop solar) fell to a low of just above 500MW. AEMO expects levels below the current record low of 458MW to occur this coming spring.
AEMO is pushing for new protocols that will allow it to “shed”, or switch off rooftop PV en masse in the “extremely rare” situations that this is required (low demand, sunny conditions, lots of rooftop solar PV) to maintain system security.
It sees this as another case for the new link to NSW, but in the meantime the government is pushing through new standards that will ensure inverters are able to ride-through any system faults, and protocols that will allow AEMO to instruct newly installed rooftop solar to be switched off when needed.
This has caused “chaos and confusion” according to the Clean Energy Council, and the Smart Energy Council has also warned that many solar installers may be left holding huge amounts of stock that are now longer deemed eligible. The list of compliant inverters and the new rules surrounding meter boxes and other protocols are yet to be released, but will affect all installations from August 10.
On Sunday, the low demand and low prices continued across the National Electricity Market, with prices at zero or below on some occasions (See graph above). However, because rooftop solar output was low in South Australia, due to cloudy conditions, only those wind and solar farms seeking to dodge negative pricing events were curtailed to zero.
Note: A static VAR compensator (SVC) is a set of electrical devices for providing fast-acting reactive power on high-voltage electricity transmission networks, and it helps regulate voltage, power factor, harmonics and stabilising the system.