Water Extraction, Ground Thermal Loss, and Land Subsidence:are Geothermal-plants Sustainable?

摘要

Geothermal energy is generally considered renewable.The resource is abundant in shallow grounds with hot water,in deep grounds with hot rocks,and deeper grounds where molten rocks retain energy with very high temperature of magma.The superficial depth is an ideal candidate for low grade heat recovery,but the most common resources matching the current technology are those that range in the medium depth range where large power plants already operate by extracting water to recover the thermal energy.The potential global geothermal resource is estimated to be as high as 2,000 GW,which is about a quarter of the current world power demand.Only about 11GW of this potential is extracted to date.Geothermal power is considered to be sustainable because the heat removal and the emission intensity are assumed negligible when compared to conventional coal-fired plants.In this paper we argue that there are geological irreversibilities such as land subsidence and thermal loss associated with geothermal plants,especially when water extraction is employed.Land subsidence could lower land surface elevations and lead to irregularities such as increased flooding,and damages to infrastructure including buildings,roads,and sewer systems.Thermal loss may cause changes in micro-climate that could impact the regional climate and beyond.We therefore infer that in lieu of some serious case studies we document,promotion of geothermal energy as clean and renewable energy should be reexamined and consented with due caution.