Development of a Low Temperature Geothermal Organic Rankine Cycle Standard

Low temperature geothermal systems are an abundant energy resource in New Zealand with over 260 sites with a resource temperature of 150°C and lower. The Organic Rankine Cycle (ORC) is the standard process for low temperature energy conversion with commercial ORCs utilizing temperatures as low as 90°C, with one site at Chena, Alaska (discussed below) utilizing temperatures as low as 74°C. The ambient temperature of the plant determines the minimum utilization temperature. Resource prospecting, power plant design, and project development are normally carried out by established companies. New Zealand is lacking experience in the design and manufacture of low temperature geothermal ORC plants. One proposed method to develop this experience is to understand the design process of existing low temperature geothermal ORCs. A qualitative analysis of ORC projects around the world can highlight the common steps involved in their development. A thematic analysis is a qualitative research method that can identify themes and patterns in data, which could help identify the common processes involved in these projects. This paper shows the outcome of our first investigation of a low temperature geothermal ORC project. The Chena ORC used for this case study is unique as it has a very low resource temperature which is only possible because it operates in Alaska, which has a very low average ambient temperature. The research material available from Chena was organized into the four key steps: prospecting, conceptual design and plant feasibility, detailed design, and construction. These steps were previously determined as important stages in ORC development. The outcome of this analysis will help to establish a guideline for developing ORCs. The number of case studies required to develop robust guidelines is unknown; however, once clear patterns and similar steps emerge from a number of case studies that should be sufficient to finalise the proposed guidelines. The final aim of this research is that industry will adopt these guidelines for their own ORC projects and eventually this will encourage development of the low temperature geothermal design standard for the Above Ground Geothermal Allied Technologies (AGGAT) research cooperative. A standard for ORCs could encourage industry in New Zealand to undertake more of their own ORC developments for utilization of both geothermal energy and waste heat and a standard should ensure that their product is on par with other ORCs produced elsewhere. The International Organization for Standardization (ISO) has a number of standards for thermal power plants that overlap with ORC components; however, there is no standard discussing the unique requirements of ORCs. Figure 1. Low Temperature Geothermal sites across New Zealand, Image from GNS [1]