Hydro Lake Storage Continues to Decline

National hydro lake storage continued its decline during August, reaching its lowest level for the year at the end of the month.

Careful management of electricity generating resources during the winter of 2006 maintained the hydro storage at levels well above the 1992 crisis year, managing to meet demand caused by 40-year record snows in the South Island and very wet conditions in parts of the North Island.

However, hydro reserves at the end of August dropped below the storage levels at the same time at end of the 1992 crisis period, highlighting a continued need for more generating capacity.

Energy managers have faced erratic inflows, new record load figures and a cold, wet winter during 2006. Despite this, they have carefully managed generation from wind, thermal and North Island hydro lakes (which benefitted from increased rainfall) to meet the increased demand and maintain supply.

At the beginning of August, national hydro storage stood at 1932 Giga-Watt hours (GWh), which was 79% of average. Positive inflows declined sharply during the 3rd week, recovering slightly at month’s end. On September 1st, national hydro storage stood at 73% of average, or 1657 GWh.

Some commentators have seized on the fact that this value is actually lower than hydro lake storage values at the same time in 1992. However, it has to be pointed out that this was achieved at the end of the winter period, and is well above storage during June and July of 1992 when storage was less than 1000 GWh during our coldest months.

Declining lake levels in the South Island were managed by maintaining North Island generation at consistently high levels, and feeding more energy from north to south via the Cook Strait cable. North-to-south transfers exceeded south-to-north transfers on 24 days during the 27-day reporting period to August 27th.

To meet this demand, North Island hydro generation was kept above 30 GWh on 16 days of the reporting period, making use of the increased rainfall in some North Island catchments. Generation from wind, thermal and geothermal sources was kept consistently high between 42 GWh and 52 GWh during most of August.

Some lessons are already apparent from this winter. Industry management changes have maintained supply during a cold and wet winter which started out with tight energy reserves, but national reserve capacity is still too low. A serious energy shortage is looming in the South Island where the lack of new infrastructure (the Clyde dam was the last large energy project) combined with the fact that the Cook Strait cable is primarily designed for south-to-north transfers will soon cause problems if “dry year” conditions persist there.

Whilst we have avoided an energy crisis this winter, we still have a serious deficit with hydro storage sitting at 73% of average as we head into spring. The water contributed by the melting of that snow which fell in the South Island is now crucial to restoring hydro storage to more favourable levels.

[Compiled from data supplied by M-Co.]

So, we have “squeaked” through another winter by a mixture of close management of resources and good luck that essential thermal plant avoided failures. We still have some serious work to do to increase our reserves for dry, cold or peak demand years. The growing deficit between generation capacity and demand in both islands (the South Island has now emerged as a more serious case) means that we have to face some difficult decisions. Perhaps the most serious is addressing the head-in-the-sand attitude which is causing us to sit on huge coal resources which would allow us to better manage the erratic hydro storage systems upon which we rely. The absence of a large modern coal-fired station close to southern coalfields deserves re-investigation in a calm, practical, open-minded fashion.

At the same time, some practical initiatives to encourage home-owners to convert to solar water heating would be timely. Perhaps the application of more “carrot” than “stick” is required to achieve this.

The stick has been liberally applied in sometimes smoggy Christchurch to discourage the use of wood fires to keep warm during winter. It seems ludicrous that we can’t accept a national responsibility to use “carbon credits” obtained from a move away from wood burning to ensure that people in population centres can keep warm with energy supplied from a new efficient coal-fired power station making use of Southland’s coal.

This is an issue that simply won’t go away, with the news that Nelson and, out-of-the blue, Arrowtown face similar controls due to air pollution from wood fires. The stick method simply won’t work. A carrot is required to encourage people to move to other heating sources in these population centres. As for the smaller towns in south Canterbury, they won’t be giving up their wood-burners after this year’s 40-year record snowfall. None of us want to see them freezing to death while power companies struggle to re-connect power lines collapsed under snow.

A bit more pragmatism and a little less ideology will allow us to make progress on these issues.

On a lighter note, my South Island friends have been conspicuously quiet this winter about their plans to unplug the Cook Strait cable and allow the North Island to float away. With the prospect of the spring snowmelt replenishing southern hydro storage, I expect that this situation will change, and that a small investment in ear-plugs might be warranted before next winter when South Island independence jerseys might make a re-appearance…

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