A technical assessment is provided of the 35 MW (net) binary power plant at the Las Pailas geothermal field, along with three alternative designs including a simple single-flash plant and a single-flash plant combined with a bottoming binary cycle, both with and without a recuperator. The status and characteristics of the wells, the gathering system, and plant/well field layout are presented. The best producing well is the northernmost one, PGP-17, close to the Rincon de la Vieja National Park; at a wellhead pressure of 8 bar,a, it produces about 135 kg/s total flow of which about 25 kg/s is steam. The unique design of the 2-unit binary power plant is discussed in detail. Plant performance is assessed based on the design specifications. Thermal and utilization efficiencies are calculated for the plant, the power cycle, the major components, as well as for the three alternative designs. Under design conditions, the Las Pailas plant has a thermal efficiency of 15.1%, a Second Law efficiency of 37.2% based on the incoming exergy of the geofluid, and a Second Law efficiency of 51.2% based on the change in exergy of the geofluid as it passes through the plant. The results of the acceptance test are presented. The analysis of data for the first 15 months of plant operation indicates that the average plant (or capacity) factor was 89.9% and the plant was available and generating power 91.6% of the time. Among the alternative designs considered, the one with the highest power output for the same geofluid inlet conditions as the actual plant was a single-flash plant optimized for peak power using the existing six production well flow curves. That alternative generated about 9.6 MW-gross more than the gross power of the actual plant, albeit at a slightly lower utilization efficiency. The highest utilization efficiency was achieved with a single-flash plant combined with a bottoming binary plant, either with or without a recuperator. No attempt was made to estimate the installed costs of the alternatives since no data were available on the actual cost to install the Las Pailas plant. (C) 2013 Elsevier Ltd. All rights reserved.