Misuse of Basslink in 2015

Basslink has just been repaired and re-connected ( http://www.hydro.com.au/about-us/news/2016-06/basslink-return-service ), hence this short review of how Basslink was used in 2015.

From an electricity systems engineering point of view the connection via Basslink of Tasmania and the mainland is a marriage made in heaven. The mainland has excess generating capacity in winter, exactly when Tasmania has its peak demand, together with the need to conserve as much water as possible for the forthcoming “dry” season. The mainland also benefits from access to Tasmanian electricity in summer, allowing it to have less of its own reserve capacity to deal with heatwave spikes in demand and/or unexpected loss of supply equipment.

Thus, one would expect mostly low flows of electricity via Basslink in spring/summer, and high flows of electricity from the mainland to Tasmania in autumn/winter. The reality in 2015 was very different.

Archived electricity data is available to the public back to May 2015, allowing us to see the extraordinary pattern of electricity generation and Basslink flow that occurred between May 2015 and the time of the break in December 2015. The following figure shows the daily average, minimum and maximum number of Megawatts, summed over all Tasmanian generators, since May 2015:


After Basslink Loss

The loss of Basslink can be seen clearly in December 2015, an event which forced Tasmania to operate in “island” mode, meeting the daily demand cycle between relatively narrow minimum and maximum limits.

Before Basslink Loss

Prior to the loss of Basslink the Tasmanian electricity system performed a daily roller-coaster ride, especially between May and August, with daily maximum generation being around double the daily minimum. Note also that the daily maxima of around 2000 MW can only have come about from every available generator operating at maximum output capacity, an extraordinary thing to do during the “wet” season, when the large water storage reservoirs should be allowed to replenish, with their associated hydro generators turned off. Tasmania was generating a substantial surplus of electricity for export between May and August, when it should have been importing.

From October 2015 Tasmania switched to being a major importer of electricity, but still had to generate around 700 MW on average of its own electricity, further depleting its hydro reservoirs, not helped by the relatively dry spring weather.


The data shown above are a smoking gun, revealing how basic principles of electricity systems engineering were abandoned during 2015.

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2 Responses to Misuse of Basslink in 2015

  1. Greg Kaan says:

    The problems started earlier with the introduction of The Carbon Tax in July 2014. Prior to that BassLink was used to support the Tasmanian dams with the option of some electricity arbitrage by exporting when the spot price was high and importing when it was low. When The Carbon Tax was introduced, however, Hydro Tasmania sold massive amounts of electricity and ran down their dam levels. Once The Carbon Tax was repealed, Hydro Tasmania did not allow their dams to recover but continued to arbitrage against the spot market without allowance for the combination of a low rain period (eg summer) and unavailability of BassLink in this period.

    Hydro Tasmania had the option of building a large amount of thermal generation or BassLink to cover low rainfall periods. Both would not have been used to an efficient capacity factor purely to back up the water storage but the cost of BassLink was largely justified by giving Hydro Tasmania the capability to arbitrage electricity in Victoria.

    Let’s look at the last 2 graphs in the following article by John Lawrence. From the text, I assume the periods are FY with the year being the June 30th position.

    There were net imports of Victorian electricity into Tasmania between 2007 and 2010 and dam levels rose in that period – Tasmania used BassLink primarily as a power source in that period.

    2011 and 2012 must have had solid rainfall as BassLink flow was largely neutral yet dam levels continued to rise. The net import for 2012 was almost certainly due to priming in expectation for The Carbon Tax.

    Dam levels then fell off a cliff during The Carbon Tax period as exports went through the roof. Rainfall in 2014 must have been good since the exports were massive yet the dam levels did not drop anywhere near the previous year.

    There is a strong case that the water levels in Tasmania’s lakes did not recover significantly after the repeal of the Carbon Tax because they continued to arbitrage. From the last graph on page 4 of the of the Marsden Jacob report, you can see that Hydro Tasmania was exporting substantial amounts of electricity to Victoria between May and September 2015. Although the Carbon Tax had been repealed, substantial amounts of wind generation have been deployed in Victoria and South Australia leading to high volatility in the wholesale spot price in the South East Australian grid, making arbitrage highly profitable for rapidly dispatchable generators. Plus there were exports even during the summers so arbitrage was definitely occuring.

    And here is an article by Mike Sandiford on the effect of The Carbon Tax on Tasmania’s water storage levels. Note the rainfall graph for Strathgordon Village which is in the Gordon catchment, confirming the solid rainfall during 2014 (FY) during which dam levels fell.

    We can argue that Hydro Tasmania was stupid/greedy to arbitrage when water levels were less than the amount needed to cover a dry spell without BassLink but the distortion of economics caused by firstly The Carbon Tax and then catering for wind (and solar) generation in SE Australia made the gamble compelling (along with the pseudo commercial operation of Hydro Tasmania where it is expected to generate dividends for it owner – the state government).

    So Tasmania’s situation has almost wholly been brought about by carbon abatement policies, both directly via the Carbon Tax and indirectly through the pricing consequences of intermittent generators favored by legislation ostensibly for carbon abatement.

    If Tasmania had not used The Carbon Tax as an income opportunity, it definitely would not have had issues when BassLink broke down. And even if they did, had they not used their hydro to arbitrage in the period after The Carbon Tax was repealed but imported sensibly to allow their dam levels to recover, they almost certainly would not have had anywhere near as big issues as they did, either.


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