A true test of ingenuity and endurance reaches its crescendo in the West Murray region this week. For seven months, inverter supplier SMA, the Australian Energy Market Operator (AEMO) and curtailed solar generators Bannerton, Broken Hill, Gannawarra, Karadoc and Wemen, have worked to resolve system-strength issues in the region using a new approach — tuning the solar farms’ SMA inverters to operate in concert, rather than individually when delivering clean energy to the grid.
“This will be a very big week,” Scott Partlin, Head of After Sales Service at SMA Australia, tells pv magazine. Partlin has co-ordinated the company’s extraordinary efforts to bring a resolution to the curtailment of the five solar farms, after it was discovered that their combined operations were the source of uncontrollable voltage oscillations triggered by normal disturbances to the grid such as lightning strikes.
Starting today (Monday 20 April), says Partlin, a comprehensive series of network tests will run every day, “which will involve each of the generators slowly bringing more of their plant online, with the control capability and settings” enabled by SMA engineers in collaboration with AEMO.
Over the past week, AEMO has been working with network provider Powercor and each of the generators — which have seen their output to the grid curtailed by 50% since September last year — to get all parties aligned for the tests.
“AEMO and Powercor, along with each plant’s consultant will then be working double time after each test to collate and check the data before moving on to the next test. It will be a planning and organisational feat!” says Partlin.
If the novel and repeatable fix works as anticipated, by Friday all generators should have completed the network testing and “will hopefully remain online thereafter”, he says.
A fortnight ago, Partlin told pv magazine about the processes that had taken place to relieve the catastrophic curtailments, which are estimated to have cost the combined solar farms $1 million a day in lost revenue. The discovered weakness in this area of the grid also subsequently led to a virtual freeze on new connections in the West Murray region, where some 45 new renewable generators are at various stages in the connection process.
Far from model behaviour
He said that prior to the introduction of highly detailed PSCAD modelling, too much generation had been allowed to connect in the West Murray area and that no-one really had a clear overview of the interactions between generators and the grid. A lack of detailed wide-area modelling which would have enabled more informed connection of generators eventually led to the problem AEMO describes on its dedicated West Murray micro site, which reports that in September, “five solar farms in the West Murray zone produced voltage ‘oscillations’ following a transmission line fault, which exceeded the regulated limits for power system security.”
Although improved modelling revealed the nature of the problem, development of SMA inverter capabilities by the company’s engineers has provided the solution, which is set to have a widespread impact on the ability of new generation to connect to challenged grids, both locally and in other jurisdictions.
Recognising an historic opportunity to make a difference to the connection of solar plant in Australia, SMA engineers travelled from Germany to meet face-to-face with AEMO so they could more quickly and comprehensively understand the problem and find an interim solution to low network and transmission capacity in areas of high renewable resource.
“As a result, the SMA experts were able to develop a new capability in the control of our inverters,” says Partlin.
Orchestrating greater harmony in the grid
The new voltage “tuning”, he explains, “gives the system conductor greater ability to time and control the generation from plants so that the combined output is optimised, with less opportunity for the different plants to get ‘out of time’” when simultaneously exporting energy to the grid.
The experience of working with AEMO’s experts on finding a resolution has been heartening Partlin tells pv magazine,: “AEMO hasn’t been so much burning the candle at both ends, as throwing the whole candle in the fire and working round the clock to try and get these generators through the tests as fast as possible.”
He says the spirit of collaboration, “bodes well for the network, for connecting generators and for the future of renewable energy in Australia”.
So does the inverter fix, which Partlin believes will allow more solar generation to be connected in challenged areas of the grid “before system strength becomes an issue”, and with fewer costly remediation requirements such as synchronous condensers which have routinely been called for to provide inertia and maintain system strength.
With AEMO having already carried out hundreds of hours of “due-diligence modelling”, Partlin reports that last week’s pre-testing of the inverter solution was extremely promising. “The new performance from the inverter showed it was stable… and looks to be exactly as AEMO has modelled for the network.”
All parties to this herculean feat of patience, diligence and reimagining technical capabilities must be looking forward to sending out a Mexican wave of thumbs-up emojis, as this week’s testing verifies the positive outcomes.
“I understand AEMO will then be working through the paperwork so the plants’ constraints can be officially removed shortly thereafter,” says Partlin.
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