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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.
For security of supply purposes, hydro storage is divided into two categories; controlled and contingent storage. Generators can use controlled storage at any time, but contingent storage may only be used during defined periods of shortage or risk of shortage. During sustained dry periods, controlled and contingent storage are important indicators of overall supply risks. South Island controlled storage, representing around 85% of New Zealand's controlled 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).
- Total controlled storage for New Zealand is below average for this time of the year.
- Over the last week controlled storage in the North Island and South Island storage decreased.
- The risk of shortage in the next two months is assessed to be low (less than 2%, barring major unexpected equipment failures).
As at 23 May Lake Taupo is at 503 GWh which is about 88% of it's maximum controlled storage. Inflows into Lake Taupo over the last week were above average for this time of year.
The graph to the right shows current South Island controlled storage relative to the assessed Riskmeter levels. The middle blue column represents South Island controlled storage. Controlled storage as of 23 May is 1772 GWh, which is about 53% of the maximum South Island controlled storage. This is below the historical average for the time of year. This amount of controlled storage places the column in the Security Watch range, which means that the risk of hydro shortage is assessed to be less than 2% (barring major unexpected equipment failures).
The graphs below show current South Island controlled storage levels and weekly inflows into the South Island hydro lakes.
Contingent storage is stored hydro that is only made available for generation at specific times to mitigate the risk of shortage. The conditions that allow contingent storage to be used differ with each hydro lake, and are governed by resource consents between the relevant local authority and generator. For more information on contingent storage and the conditions of its use, refer to the document below.
Contingent Storage additional information [ pdf 342.65 KB ]
Current available contingent storage is shown on the following graph: