Hydro Lake Storage Declines Further

New Zealand’s hydro-electric lake storage levels continued to decline during September 2007 going against the trend of recent years. Inflows were generally below average, and demand was higher than last year.

Hydro lake storage stood at 1852 GWh (GigaWatt hours) 82% of average at the beginning of September 2007, and had declined to 1630 GWh 72% of average for the time of year by month’s end. Whilst total storage was below average throughout September, levels were above or equal to last year’s for the first 8 days of the month, and on the 16th and 17th, but otherwise the storage situation was worse than last year. Storage was above that recorded during the dry year 1992, but below 2004 figures.

September’s dry weather was reflected in below average inflows to lakes on 22 days. On September 30th, inflows received a much needed boost (146% of average) following heavy rain in catchments.

Demand exceeded last year’s figures on 21 days, peaking at 121.7 GWh on September 6th, well above last September’s peak load of 112.8 GWh. As expected, the September peak was lower than monthly peak loads for the last three months, reflecting warmer weather.

Transfers via the Cook Strait cables followed the normal trend, with south-to-north transfers exceeding north-to-south on 23 days.

Once again, the springtime inflows to South Island lakes will be crucial if hydro storage is to recover in time for next winter.

Whilst preparing this September report, additional information came to hand. In a bizarre move, it was announced that Transpower had disabled one of the two Cook Strait electricity links early in October. The aging 40-year-old technology (called pole 1 by those in the industry) had been expected to remain in service until 2010, by which time a replacement should have been in service.

However, Transpower disabled the link for unexplained reasons ahead of a report on remedial action which is due at the end of October. Meridian Energy claims the move caps the output of the Benmore dam at 2/3 of its maximum meaning that, at a time of shortages elsewhere, we could be in the embarrassing position of spilling water from an overfull Benmore dam instead of using it for generation.

The pole 1 technology is expected to take 3-4 years to replace, so a permanent shutdown at this early stage would add another element of threat to the ability to maintain electricity supply at a time of low lake levels. And, if the springtime South Island replenishment does not occur, this could be our situation next winter.

[Compiled from data supplied by M-co.]

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