Dealing with droughts10 December 2008
Hydro Tasmania has notched up almost a century’s experience within the hydro power industry. However, it is only within the past two years that the Australian utility has had to face its worst drought events. IWP&DC spoke with David Marshall, manager of energy resources, to discover how hydro resources are faring
Hydro Tasmania’s hydro power scheme is an integrated system of 28 power stations, numerous lakes and over 50 large dams. We supply most of Tasmania’s electricity and also provide peak power in the National Electricity Market. Over the past ten years we have experienced below average inflows into our hydro storages, and over the past ten months only 64% of expected inflows arrived into Hydro Tasmania’s storages.
We have experienced several significant drought events in the past but the last two years have been among the worst we have ever seen. We believe that there has been a shift downwards in our rainfall and that we can expect a future where the average inflow into our storages will be up to 10% less than it has been.
The Basslink interconnector is the world’s longest undersea electricity cable and enhances security of supply on both sides of the Bass Strait; protecting Tasmania against the risk of drought-constrained energy shortages while providing Victoria and southern states with secure renewable energy during times of peak demand.
Basslink is critical to Hydro Tasmania’s operations. If it hadn’t been available during this drought period, there is no doubt that some form of power restrictions would have been put in place. Without it our hydro storages would be much lower.
Prior to Basslink we had limited gas generation and were forced to gradually draw on storages. Eleven years ago our combined storage level was at 85% full. Today it stands at about 21%. In order to preserve storages we are now importing energy across the Basslink and using gas generation. Demand continues to grow so, with the expected lower rainfall, generation from gas and wind and importing over Basslink are all very important.
Since it was commissioned in April 2005, we have imported a net of more than 4100GWh across the Basslink: equivalent to about 28% of our storage capacity. In June 2008 we imported 194GWh of energy across Basslink and only exported 5GWh. In comparison, 135GWh were generated by the Bell Bay gas-fired power station.
In the 2006/7 financial year Hydro Tasmania spent around A$100M in Basslink imports and gas generation to ensure security of supply. The result for last year is likely to be very similar.
Lowdown on maintenance
Lower storage levels can mean different maintenance requirements. On some lakes, where water levels get very low, we sometimes have to dredge the lake around the intake to reduce the amount of mud that gets sucked through into the power station. Like this we can help prevent damage to the turbines.
For dams that have very low reservoir levels, eg Miena dam (Great Lake), we reduce the frequency of the inspections as there is not the same element of risk when the dam is no longer under a normal working load.
When the above reservoirs return to normal working levels, ie when the drought is over and it rains a significant amount, we perform extra inspections on the affected dams similar to what we would do on a dam that is filled for the first time. This looks in close detail to ensure the dam is performing as expected when the pressure of water loading is added.
We also have an extensive environmental monitoring programme that becomes more intensive as storages get lower. As far as we are able, we adjust our operations to minimise the risk of damage to water quality and species habitat.
|Sowing the seeds|
Hydro Tasmania initiated its cloud seeding programme over 38 years ago. Described as being a cost-effective way to increase rainfall over hydro storages, the utility now spends A$1.3M annually with an estimated cost/benefit ratio of around 3:1.