The previous post looked at the electricity data from Tasmania on the first full working day after the restoration of Basslink. This post looks at the electricity data for the first full working week of the newly restored Basslink.
The following figure shows total supply (blue), demand (red dots, obtained by subtracting the MW flow of Basslink from total supply), the outputs of the key hydro basins (those with large but depleted water storage reservoirs), and total wind power:
The restoration of Basslink can be seen on the first day (Monday 13th June), after which Tasmania sustained a modest export of “surplus” electricity, in fact it was so determined to export something, and/or to avoid importing, that the Gordon hydro basin (amongst others) was used for brief periods to meet (and sometimes exceed) demand peaks.
The following electrical characteristic of Basslink may be one reason why Hydro Tasmania is reluctant to switch backwards and forwards between import and export:
“Due to the minimum hold on current characteristic of the thyristor based converters the Interconnector has a minimum power flow threshold of 40 MW and the submarine cable requires a 2 minute deionisation time when reversing power flow.”
Source of above: http://www.basslink.com.au/basslink-interconnector/operations/
This issue with low and reversing Basslink flow may partly explain the large jumps between import and export flows seen in the data shown below, and in other days looked at in 2015.
The use of the Gordon hydro generators in the current “wet” season is a bit worrying, as their associated lakes still have highly depleted (though growing) reserves, but so far the use of Gordon has been very modest compared with what happened a year ago, a representative example of which is shown again below for 18th June 2015:
The heavy use of the Gordon and Esk generators in previous “wet” seasons prevented their associated lakes from being properly replenished, a major contributory factor to them having very low levels today.
Maybe the hydrologists at Hydro Tasmania should turn off Gordon and Esk and hide the keys until the spring, now that Basslink is available to import any shortfall in electricity.