Close eye on lakes and power

The electricity industry is keeping a close eye on likely winter power supply as falling South Island lake levels push spot prices up and North Island power gets sent south.

Weeks of dry weather have caused the normal south-north flow on the interisland high-voltage direct-current (HVDC) link to be reversed at peak times.

The Electricity Commission's draft outlook for winter 2010, published late last year, says there should not be a problem with security of supply this winter or the next two winters, and is not seeking extra sources of electricity "at this point".

But inflows to southern hydro-electric lakes over the last month were only 73 per cent of average, at 365 gigawatt hours (GWh), and key Meridian lakes Manapouri and Te Anau were yesterday only 48 per cent and 49 per cent full respectively for generation.

Lake Pukaki was 87 per cent full and Lake Tekapo was 84 per cent full.

Figures from the National Institute of Water and Atmospheric Research show that river flows in the hydro lake catchments last month were extremely low. Flows were "far below normal" into lakes Manapouri and Te Anau and into lakes Wanaka and Hawea, and "below normal" in the Waitaki lakes catchment.

The high value of South Island hydro power has seen South Island wholesale prices spike as high as 18c a kilowatt hour (kWh), or unit, although they fluctuate wildly when North Island thermal and wind power is sent south.

Electricity Commission chairman David Caygill said the final decision on whether extra sources of power might be needed this winter would be released soon.

"The essential conclusion we've reached in the draft is we don't think we will need to procure any extra capacity this winter or next, but we are slightly concerned about the situation by 2013."

Caygill said plans for new power stations were unsurprisingly dropped when the economy went into recession, but this year Contact Energy had a new plant at Stratford and Mighty River Power had just completed the second of three geothermal stations in the Bay of Plenty.

Meridian Energy spokesman Alan Seay said it had been very dry in the catchments of Manapouri and Te Anau.

"But that can change with a day's rainfall down there. We're about average in the Waitaki – it's been very dry in the Waitaki catchment too but that's not unusual for this time of year."

Auckland power consultant Bryan Leyland said spot prices had been ramping up steadily and had not recovered as expected when Contact's Otahuhu B station came back on line this week.

"I believe everyone in the industry is beginning to get concerned. Prices are higher in the South Island indicating that South Island generators are getting more and more nervous.

"The probability is that it will rain, but the risk is that it won't."

- © Fairfax NZ News