Report: TR 2002/22

Author: Sinclair Knight Merz Limited

Abstract

Estimates of resource capacity, expressed as equivalent electrical generating capacity using current technology, have been made for geothermal systems in the Waikato region, using a stored heat approach and resource lifetimes of 30, 100, 200 and 300 years.

Total generating capacity for the Waikato geothermal fields is estimated to be 3100 MWe, for a 30 year resource life and using median resource parameters.  Summing the 10th and 90th  percentile estimates for the individual fields (which gives a greater than 90% confidence) realistic minimum and maximum values of 2200 and 4400 MWe are obtained.  Increasing the resource life to 300 years, and using natural heat flow as a the lower limit on extraction rate, total generating capacity falls to about 420 MWe (median value). 

Generating capacity based on natural heat flow is greater than 40 MWe in four geothermal fields: Wairakei, Waimangu, Waiotapu-Waikite and Rotokawa.  Estimates based on natural heat flow can be considered potentially physically sustainable, minimum capacities, although this does not mean that extraction at that level would have zero environmental effects. 

Resource capacities based on stored heat do not necessarily provide a good indication of long term productivity.  In addition to stored heat, productivity is dependent on factors that may only be quantifiable when the resource is produced, such as susceptibility to groundwater incursion, or the ability of the system to provide enhanced recharge of hot fluid from the system upflow.

The capacity estimates presented in this review are based on currently available information for the individual fields and Sinclair Knight Merz’s knowledge of analogous systems in New Zealand and overseas.  It can be expected that the capacity estimates will be refined as more information becomes available.

Resource Capacity Estimates for High-Temperature Geothermal Systems in the Waikato Region [PDF, 364 KB]