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.