Hydro Lakes Recover in November

Hydro storage lakes recovered from a decline that set in during October and passed above 100% of capacity for only the second time during 2008 on November 24th.

New Zealand’s hydro-electric storage lakes stood at 2364 GWh (GigaWatt hours) at the beginning of November 2008, 97% of average for the time of the year. Levels declined slightly during the first half of the month before improving from November 16th. Levels broke through 100% of average on the 24th and remained above average for the remainder of the month. At the end of November, storage was 3076 GWh, 116% of average for the time of year.

Inflows were below average on 20 days, but massive inflows on the 17th and the four days from the 24th to the 27th helped levels to recover. The equivalent of 320 GWh of energy surged into storage lakes on November 25th when inflows reached a massive 380% of average.

Interisland transfers followed the normal pattern, with south-to-north transfers via the Cook Strait cables exceeding southbound on all 30 days. No energy at all was sent southward on 20 days during November.

After matching weekdays and weekends, demand was consistently lower than that for November 2007 on all 30 days. Peak load of 108.5 GWh occurred on November 7th – peak load of 112.3 GWh was drawn on November 6th in 2007.

Average daily demand during November 2008 was 99.4 GWh compared with 105.2 GWh in November the previous year. This represents a load reduction of 5.5%.

Allowing for variations in weather conditions and other factors, most of the reduction can be explained by a transformer failure at the Tiwai Point aluminium smelter late on Sunday November 9th which caused the smelter to reduce production by about a third. The plant uses about 15% of New Zealand’s electricity, and had been working to a 10% cut to consumption while wholesale power prices were high due to low hydro lake levels.

The transformer failure occurred before the plant returned to full production following a late winter recovery in lake levels. The smelter’s load reduction of one third accounts for about 5% of New Zealand’s electricity production.

[Compiled from data supplied by M-co.]

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