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Hydro Generation

Background

Hydroelectric generation contributes around 60% of New Zealand's total electricity supply, with many generators of widely varying sizes distributed throughout the country.

Inflows (rainfall and snowmelt) can be stored in hydro lakes until needed. The most important are Lakes Tekapo, Pukaki, Hawea, Manapouri, Te Anau, and Taupo. The lakes have quite limited operating ranges - for technical and resource consent reasons, each lake's level cannot be lowered below a certain point. It is not possible to completely 'empty' a hydro lake! In the absence of inflows, the lakes can only hold enough water for a few weeks of winter energy demand.

During sustained dry periods, hydro lake storage levels are important indicators of overall supply risks. South Island lake storage, representing around 85% of New Zealand's hydro storage capacity, is often used as a key measure. Storage is expressed in gigawatt-hours, GWh (a measure of the energy that can be produced using the water).

Current Hydro Situation

Total New Zealand storage is below average for this time of year.
Over the last week North storage increased and South Island storage decreased.
The risk of shortage in the next two months is assessed to be low (less than 1%, barring major unexpected equipment failures).

New Zealand Hydro Risk Curves

The graph below compares New Zealand hydro storage to the Hydro Risk Curves. As of 20 May 2012, storage is below average for the time of year, and the risk level is Security Normal.

Latest New Zealand Hydro Risk and South Island Hydro Risk Curves [95kB]

Hydro Risk Curve Methodology Explanation [537kB]

Hydro Risk Curve Input Assumptions (September 2011) [209kB]

Simulated Storage Trajectories from September 2011 [116kB]

Simulated Storage Trajectories (South Island) from March 2012 [208kB]

Simulated Storage Trajectories (NZ and SI) from May 2012 [182kB]

September 2011 Hydro Risk Curves [25kB]

Click for further information about the hydro risk curves.

North Island Storage and Inflows

As at 20 May 2012 Lake Taupo is at 278 GWh which is about 54% of total storage. Inflows into Lake Taupo over the last the week were higher than average for this time of year.

South Island Storage and Inflows

The graph to the right shows current South Island storage relative to the assessed Riskmeter levels. The middle blue column represents South Island hydro storage. Storage as of 20 May 2012 is 1591 GWh, which is about 52% of total storage. This is below average for the time of year. This amount of storage places the column is in the Security Normal range, which means that the risk of hydro shortage is assessed to be less than 1% (barring major unexpected equipment failures).

The graphs below show current South Island storage levels and weekly inflows into the South Island hydro lakes.

Inflows into South Island hydro catchments are usually at their lowest between June and August, and at their highest between November and January.

Related Information

Risk Curve Explanation