Hydro Storage, June 2008

New Zealand’s hydro-electric storage lake levels increased slightly during June 2008, benefitting from improved inflows and a reduction in demand.

At the beginning of June 2008 New Zealand’s hydro storage lakes stood at 1534 GWh (GigaWatt hours), 54% of average for the time of year. By month’s end, lake levels had increased by a small amount to 1536 GWh, being 57% of average for the time of year, June being a month in which lake levels usually decline.

South Island lake levels continued to decline during June, while rainfall fed North Island lakes allowing southern storage to be tightly managed while northern plant met demand. National inflows were above average on 19 days, showing the influence of heavy rain events.

To preserve southern lake levels, north-to-south transfers via the Cook Strait cables exceeded northbound transfers on all 30 days. The more usual south-to-north transfers stood at zero on most days, with only tiny amounts of electricity being transferred northward on the 4th and 5th of June.

Day-for-day demand measurements, which match weekdays and weekends show that daily demand was less than the same day last June on 24 days. Peak demand during June 2008 occurred on the 30th when 120.3 GWh of energy was drawn. Last June, peak load was 131.9 GWh on the 28th.

Average daily demand during June 2008 was 109.25 GWh compared with 114.56 GWh during June last year. Comparing figures for the calendar months shows a nett 4.6% reduction in load during June 2008, reflecting savings achieved by the industrial and commercial sectors and the residential savings campaign.

Unlike other figures attributed to the residential savings campaign, this nett figure of 4.6% is not adjusted for temperature and other factors and shows the actual reduction in load compared with June last year.

The Minzone calculation, which determines the point at which low lake levels require all thermal plant to be online and generating was adjusted during June 2008. A small increase in thermal capacity allowed the Minzone to be adjusted downward and the Emergency Zone, the point at which the Electricity Commission can impose electricity conservation measures, to also be lowered. Nevertheless, New Zealand’s hydro lake levels remained well within the Minzone, requiring thermal plant at Whirinaki and elsewhere to be run at full capacity to conserve hydro storage.

[Compiled from data supplied by M-co.]

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