Alternative Energy Carriers for Remote Geothermal Sources

Abstract

Australias geothermal industry will soon be ready to scale up its capacity from pilot-scale projects of one MW or less, to demonstration plants of several tens of MW. These scales are too small to justify construction of high-capacity long-distance electricity transmission lines connecting to the national grid. As illustrated in Figure 1, Australias primary geothermal sources are much closer to the national Compressed Natural Gas (CNG) pipeline network than they are to the national electricity grid. This paper presents an assessment of the prospect of using large-scale electrolysis to convert the output of a geothermal demonstration plant to hydrogen and then to methane for direct injection into existing CNG transmission pipelines. The methanation step involves the consumption of carbon dioxide from the CNG processing plants - a byproduct that would otherwise be vented to the atmosphere. A summary of energy flows is given towards the end of this paper. The key advantage of the use of hydrogen and methane as alternative energy carriers is that it would circumvent the dilemma: What comes first - commercially viable electricity transmission lines or a successful industrial scale demonstration plant?.