Hydro Lakes Remain Low

New Zealand’s hydro-electric storage lake levels remained low during the first fortnight of June 2008, with anticipated rain maintaining the status quo.

At the beginning of June 2008, New Zealand’s hydro storage stood at 1534 GigaWatt hours (GWh), 54% of average for the time of year. Levels declined toward 49% of average on the 12th before much anticipated rainfall in Fiordland boosted levels to 1473 GWh on June 14th, 53% of average for the time of year.

Inflows hovered around 50% of average during the first five days of June, before rising slightly between the 6th and 8th. Once again inflows languished until the 13th when they were above average ”“ being 109% on the 13th and 176% on the 14th. Despite these small daily boosts, inflows calculated on a weekly basis have been consistently below average since early January reflecting the dry conditions.

Demand declined during the first fortnight of June, with average daily demand being 108 GWh compared with 115 GWh per day in June last year, and 117 GWh in 2006. This represents a reduction of about 6% on last year’s consumption largely due to savings made by commercial and industrial users. A public energy savings campaign was launched on June 14th, and it is hoped that this will drive demand down further, but a savings target has not been set.

Storage is being tightly managed, with the southern hydro lakes being shepherded through the dry spell. North to south transfers via the Cook Strait cables have exceeded the more usual northbound transfers on all 14 days. Only tiny amounts were transferred northwards on the 4th and 5th of June, transfers sitting at 0 GWh on the other 12 days.

Provisional figures for Sunday the 15th of June indicate healthy inflows of 166%, raising storage to 55% of average for the time of year. This represents the tail-end of the heavy rainfall in Fiordland over that weekend when a much-anticipated weather pattern brought heavy rain.

Despite the slight rally, lake levels remain seriously low as the country heads into the coldest winter months. Nationally, water levels remain firmly in what is called the Minzone, the minimum lake storage level required to ensure continuity of supply based on projected demand and the availability of generating plant and transmission facilities.

Once New Zealand enters the Minzone, all thermal plant must be running and all hydro generators must be conserving water to the maximum extent possible, according to the Electricity Commission. Entering the Minzone also causes the Crown-owned Whirinaki reserve energy power plant to come on-line and run at its maximum output if it has not already been activated by high market prices.

The Minzone calculation is somewhat complex and changes dynamically as plant is taken out for maintenance. For example, when part of the de-commissioned gas-fired plant in Taranaki became available, the Minzone was recalculated. It also has to factor in the run-down of hydro storage over the high demand winter months, the ability to transfer power between North and South islands, hydro plant which must be run regardless of load etc.

In essence the Minzone is modelled on 77 years-worth of records of inflows to hydro catchments. Entering the Minzone means that New Zealand has encountered a 1 in 77 scenario that, if patterns repeat, could result in empty reservoirs if action is not taken.

Our present hydro storage levels fall toward the bottom of the Minzone calculation, just above the Emergency Zone. A pdf file of the Minzone for the 19th of June 2008 can be found here. The Emergency Zone marks the point at which the risk of shortage has increased to 1 in 10. The commission’s website notes, “At the Emergency Zone, the Electricity Commission will institute an emergency conservation campaign, with public messages and possible other measures to induce reduction in electricity usage.”

[Compiled from data supplied by M-co. Minzone information sourced from Electricity Commission website.]

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