An Alaska case study: Organic Rankine cycle technology

Abstract

Organic Rankine cycle (ORC) technology is mature for larger-scale power generation, but ORC systems appropriate for smaller-capacity generators, typical of Alaska village and other Arctic community power plants, are still new to the market or in the prototype phase. Many villages are being approached by product developers to invest in this new technology, and there is a significant value in the dissemination of the real world performance and costs of existing systems. In this analysis of ORC installations across Alaska, capacity factors ranged from 33% to 52%. Low utilization levels are attributed to insufficient waste heat resources (in Unalaska and Cordova) and to higher than expected maintenance costs in a prototype pre-commercial model (in Tok). Significant annual fuel savings have been realized for each installation, with annual demonstrated savings of $70 000 in Unalaska and projected annual savings of over $300 000 in Cordova. Modifying existing generation for an ORC system has proven to be challenging and expensive. Project cost data indicate that Alaska projects should expect total capital expenditures to be two to three times the cost of the ORC unit itself. Some systems have been highly reliable and cost-effective, while other installations have been neither. The most cost effective ORC system may be best implemented with a ground-up new generator design and install. Of the installations in Alaska, only the Unalaska Green Machines have achieved reliable operation beyond a few weeks. The smallest reliable system, which operates in Unalaska, has a 50 kW nameplate capacity and requires 500 kW of waste heat, indicating that this technology is best suited for communities with 1 MW or more of diesel generation.