The river room

Energy NZ spends a morning in Mighty River Power’s Trading Room in Hamilton, watching the harnessing of the mighty Waikato River.   BY ALAN TITCHALL

Lee Bennett has just finished what must be one of the more exclusive training programmes in the country. After six months’ supervision, he’s a fully qualified dispatcher with Mighty River Power (MRP), controlling the flow of the Waikato River and its hydro system. On a 12-hour shift, Bennett is in charge of the river’s flow from the Taupo catchment, down through the nine hydro stations on its way to the coast.

Under MRP’s consent, the Waikato must always run. The water must always leave Taupo and be able to pass through the last dam on the river, at Karapiro. It takes around 24 hours for it to travel this length of the river, and the dispatcher must use its passage through each power station to produce electricity from the system as efficiently as they can. And it’s a job subject to enough factors to make this a test of human – rather than computer – skill.

The maximum generation the Waikato hydro system can produce is 1050MW (20 to 25 percent of the North Island’s peak power), or about the same amount as the coal-powered Huntly station on a good day. As the river must be kept moving, the minimum output from the system is 53MW. The dispatcher works their shift in close association with a trader, who sells the electricity on the open market through the EMCO wholesale clearing centre in Wellington.

Mighty River Power’s generation headquarters, known as the Trading Room, is sandwiched between a bunch of schools on Peachgrove Drive in Hamilton. Since 1993, the Waikato River hydro system has been controlled from this location, using seven dispatchers and seven traders, covering 12-hour shifts. They’re part of a total staff of 26. Since the early 1990s, the nine power stations (and eight dams) along the Waikato have been completely unmanned, with maintenance and security handled by sub-contractors on call-out.

Our visit to the Trading Room coincides with the driest summer on record for almost 100 years and, consequently, buoyant electricity prices. Although the Waikato region is in drought and looks like a blowtorch has gone over it, there’s plenty of river flow, and MRP has only used half of its Lake Taupo resource, which is one percent of the total water or 1.4 metres of lake level.

Water management is a carefully timed balancing act, holding and releasing water between the different-sized dam reservoirs. And this requires thinking 12 hours ahead to the next dispatching shift and months into the future. What do you store for tomorrow and what you need now for generation?

Each dispatcher faces a different challenge in this task and there are many variables, says Bennett. Thirty percent of the river volume comes from contributories along its flow, and even a small swing in river temperature can affect power production. There’s no computer in the world that could cope with the second-guessing involved.

Then, there are the river communities: the duck shooters, fishers, canoeing regattas and other stakeholders, also reliant on the level and flow of the water. They include the MV Waipa Delta paddle steamer, which relies on the Trading Room for its annual overhaul. Not having access to a dry dock, the steamer squats over a sand bar once a year, while the dispatcher lowers the river until its hull is sitting out of the water.

Open market trading

The dispatcher and trader work each shift together like Siamese twins, producing and selling electricity as the market demands. Sales go through the EMCO, which was set up in 1996 as an independent body to administer the wholesale electricity market and manage its daily pricing. This is based on bids and offers from generators, purchasers and traders.

Working in real time, the EMCO trading platform sets a new price per megawatt hour every five minutes. These can vary depending on daily and seasonal market demand. In an extreme situation, with a big spike in generation, the price of a MW has varied between $70 and as much as $500, says Andrew Anderson, the trading operation manager for MRP.

“Most days are generally stable, with smaller variations of between $10 and $15 per MW hour,” he adds. “The price will vary more in the middle of winter, between morning and evening peaks.”

The drought ravaging the country at this time has lifted the price to $70 per MW at night and $150 during the day.

“Normally, at this time of the year, the price would vary between $30 and $50 between day and night,” says Anderson.

Frequency keeping

A hooter alarm, like the crash dive warning in an old submarine, blares over our heads. It goes off quite a few times while Lee Bennett does his dispatching. 

“It’s Transpower letting us know that we are picking up frequency keeping,” he says, making an adjustment with his computer mouse and yelling out what he’s done to the trader.

The country works on 50 hertz, and maintaining this frequency is critical to the welfare of every machine nationwide that runs on electricity. A select number of power generators in New Zealand operate as frequency keepers, and they bid for this service. In the North Island, these include hydro generators MRP and Genesis. Hydropower generation is quick and instant, so best suited for keeping frequency stable.

On the day of the magazine’s visit, MRP was the frequency keeper for the North Island, using Maraetai, its largest power station, to keep frequency within a tolerance of 1.5 hertz of the 50-hertz level. A large wall clock in the trading room, with red digital figures, flickered constantly between 49.10 and 50.10 hertz

Bennett has five screens in front of him, controlling the 39 generators along the hydro system. Faults come up like emails, each one a colour denoting its urgency: red means ‘get a move on’. A number of warnings, I note, are related to cleaning. With the river low, weed clogging the screen over the intakes has become a nuisance.

In between the frequency hooter, and phone-ins from maintenance crews, Bennett’s watch is looking uneventful.

“It’s a fairly forgiving river,” he says, casually scanning the bank of LCD screens.

Nothing dramatic has occurred on his watch over the past six months he adds, recounting the time on someone else’s stint when lightning took out a generator at Aarapuni, shutting the entire station down.

“You can’t always expect a quiet day.”