Celebrating 50 years of steam

New Zealand was one of the leaders in harnessing underground steam to generate electricity.

We built the second geothermal power station in the world and were the first to use wet steam (a mixture of steam and hot water). Kiwi engineers are credited with inventing the steam–water separator for this purpose.

The first attempts to harness steam for electricity generation were carried out at Larderello in Italy, where the world’s first geothermal power station was opened in 1913. New Zealand army engineers serving in Italy during the Second World War were sent to inspect the station in June 1944, only to find retreating German forces had destroyed it.

Kiwi engineers visited the Italian site again in 1948, when the power station had been rebuilt and was producing over 140 megawatts of electricity. Back in New Zealand, two dry years in a row had meant that hydro-electric dams could not produce the country’s energy requirements. Another source of power, independent of imported oil, became imperative.

The next year, 1949, exploratory drilling began at Wairakei where the Department of Scientific and Industrial Research (DSIR) had already succeeded in harnessing steam for the Wairākei Tourist Hotel by drilling to 170 metres. The Waikato River nearby was a perfect source of cooling water for an early geothermal generation.

The power station was built between 1958 and 1963, the second such plant in the world, and the first to attempt to harness wet steam, a mixture of steam and hot water, in contrast to Larderello’s use of dry steam. Engineers invented a steam–water separator, and had to pioneer ways of overcoming numerous other problems with wet steam harnessing, and our expertise became highly sought-after by countries interested in developing geothermal resources.

Interestingly, the original Wairakei geothermal project was initially a joint venture between the New Zealand government and the United Kingdom Atomic Energy Authority (UKAEA) to produce power and heavy water. Heavy water (in which both hydrogen atoms have been replaced by their heavier isotope deuterium) is used to slow down the nuclear fission process that occurs in thermal nuclear reactors. It can be made by distilling ordinary water, but this process uses a lot of energy and geothermal heat was thought to be an ideal energy source. The idea was first suggested at a conference in Rotorua in 1946, and in 1954 funding was approved. However, the costs proved to be prohibitive, and the UKAEA pulled out of the project in 1956.

The pioneering zeal of the 1950s and 1960s was followed by a lull during the 1970s and 1980s, when attention turned to the large Maui natural-gas field and, despite the success of the Wairakei project, it was not until the late 1980s that further geothermal power stations were built – at Ohaki and Kawerau. By 2002 New Zealand had seven geothermal power stations; six in the Taupo volcanic zone, and one at Ngawha in Northland. Developments since then include station expansions  – Rotokawa 2, Mokai 2 and 3, the Wairakei binary plant and the recently commissioned 90MW Kawerau plant. Geothermally generated electricity provides around eight percent of New Zealand’s total electricity. Our geothermal energy potential is estimated to be around 1200 megawatts of baseload renewable generation and ultimately supply a third of our total electricity needs if fully developed.

The advantage of steam is that it is (baseload) renewable, and currently Kawerau is pumping out more electricity than all the existing wind farms in New Zealand.

Geothermal power stations also have a capacity factor of almost 100 percent.