Serious Decline in Hydro Lake Storage

New Zealand’s hydro-electric lake levels passed below storage levels at the same time last year on April 22nd and, since the beginning of April, the steady decline has closely paralleled the trend seen during the energy shortage year 1992.

At the beginning of April 2007, New Zealand’s national hydro storage stood at 2834 Gigawatt hours (GWh), 91% of average for the time of the year. During the month, storage steadily declined to sit at 2215 GWh or 73% of average for the time of year at month’s end.

Inflows to the storage lakes were above average on only 1 day during April, with the month showing a declining trend. Weekly inflows, which give a smoother picture over daily figures showed a slight recovery in the week ending May 4th, when the weekly inflow reached 66% of average (302 GWh).

Low storage levels at this time last year required tight management through the winter months to avert serious shortages. Whilst daily storage was above last year’s figures for the first 21 days of April, it passed below that level on the 22nd and has remained there. Since the beginning of April the declining storage trend has been tracking parallel to the decline seen in the crisis year 1992 whereas, during April last year, hydro storage rose during April.

The Cook Strait cable normally carries energy from the large southern hydro schemes to the North Island. This continued during April, but it also carried light southward transfers on 22 days. It appears that pylon maintenance being carried out near Tawa in recent months has just been completed, so it seems likely that the inter-island link will soon be running at higher flows in the near future as energy managers begin protecting the declining hydro storage.

[Compiled from data supplied by M-Co.]

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