The 30 MW Rotokawa geothermal project was the first geothermal project developed in New Zealand by private sector interests following the deregulation of the electricity industry. The project is unique in its structure and technology: In its structure it is a joint venture between the Tauhara North No 2 Trust, the indigenous land-owner and the state-owned
generator, Mighty River Power and in its technology as it uses high pressure steam of above 25 bar as its resource. The project has two production wells of around 2000 metres depth producing two-phase fluid and three reinjection wells of 500 metres depth. Steam is separated from the brine at ~25 bar and both the steam and the brine are used for electricity generation. The condensate is pumped up to the brine pressure,
combined with the high-pressure brine, and reinjected with no further pumping. A 14 MW backpressure turbine is utilised to drop the steam pressure to ~ 1.5 bar. This steam is condensed in two binary units of 5 MW output each. This configuration, called by ORMAT a Geothermal Combined Cycle Unit, has the advantage of the low capital cost of a simple backpressure turbine and of condensing the steam in a shell and tube heat
exchanger where steam wetness is not a problem. There is a third 5 MW binary unit, utilising the hot brine flow. Analysing the 5-year performance of the plant it can be stated that the Rotokawa plant is probably the most efficient operating geothermal plant in the world. A summary of the plant performances is presented and analysed.

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