How is energy security measured?

The headline storage figure often quoted in the media is Total Energy in Storage (TEIS), which simply means the total amount of water we currently have in all of our storages. It’s expressed as a percentage of the total combined storage capacity, for example 36.1 per cent.

Since 2016, we measure and manage storage security using Tasmania’s Energy Security Framework.

The Framework includes measures to monitor energy security during drier periods, including the High Reliability Level (HRL) and above that, the Prudent Storage Level (PSL).

• The HRL sits at the top of the energy security reserve. Even if Tasmania experienced very dry weather AND a six-month Basslink outage, we’d still have enough energy in storage to maintain Tasmanian supply.
• The PSL is the early indicator that we need to adjust our operations accordingly to maintain water storages.

Tasmania’s energy security is measured by comparing the storage figure against the High Reliability Level.

Dropping below the PSL threshold

That’s bad, right? Actually no. Dropping below the PSL is not cause for alarm.

Storages crossed the threshold in 2019, and again in August 2022. We are expecting these fluctuations of dipping in and out of PSL to continue over the coming weeks and months due to dry conditions.

It is completely normal for storages to move above and below the PSL during drier periods.

We respond by adjusting our operations accordingly to maintain water storages. That is exactly how the Energy Security Framework is intended to operate.

We work closely with the State Government to actively manage water storages. That can include importing more energy and exporting less or, if required, firing up the Combined Cycle Gas Turbine (CCGT) at the Tamar Valley Power Station.

So let's talk about TEIS

TEIS hardly ever goes above 50 per cent or below about 25 per cent.

It generally peaks in the 40s during the wettest part of winter and spring each year, and bottoms out in the 20s in the driest part of autumn and summer. Both levels are normal and secure. They just represent different extremes in the seasonal cycle.

Curious about why TEIS doesn’t ever really go above 50 per cent?

A 100 per cent storage level reflects the absolute maximum amount of water that a lake or lagoon can actually hold. But in reality, the water never gets anywhere near that level. And it shouldn’t.

At 100 per cent full, the lake would be much larger than its ‘normal’ size and appearance. Boat ramps and fishing spots would be underwater, and you’d face the possibility of flooding with just a sprinkle of rain or a puff of wind.

Lake that aren’t hydropower catchments are naturally kept in check by rivers and evaporation taking water away.

Natural factors aside, building up storages to very high levels would be very inefficient, and commercially speaking, all of that unused water represents a huge amount of clean hydropower that we’d failed to generate.

Want to find out more?

The Tasmanian Economic Regulator (TER) releases an Annual Energy Security Review every November, along with monthly dashboard updates, assessing Tasmania's energy security at a point in time. These reports are available on the TER website.

Because more than two-thirds of Tasmania’s energy comes from hydropower generated right here in Tasmania, there’s often great interest in our water storage levels, and how we manage them.