Solar Thermal Energy In Thimphu, Bhutan - A feasibility study using TRNSYS modeling

Abstract: Bhutan is one of the highest per capita users of firewood in the world. Firewood and electricity are the most common methods for heating in Bhutan and both methods suffer from drawbacks. Bhutan’s capitol, Thimphu, lies some 2500 meters above sea level and has cold winters with clear skies. These facts are the base for this report’s investigation of the potential to use solar thermal energy to mitigate the use of firewood and electricity for heating. Fieldwork and interviews were carried out in areas in and around Thimphu. Two models were made; one for a typical rural house, heated with firewood, and one for a typical urban apartment complex, heated with electricity. The rural house was modeled as a two story building with one family living on each floor. The urban apartment complex was modeled as a four story building with four apartments on each floor for a total of 16 families living in the building. These models were input into the simulation program TRNSYS. A solar thermal system was optimized for each house based on performance while trying to keep the system as small as possible. The effects of this system on the comfort and energy consumption in the rural and urban model were noted. In the rural case a solar thermal system with a solar collector area of 15 m2 and a tank volume of 0.65 m3 decreased the firewood usage over a year with 50 % while increasing the comfort level. In the urban case a solar thermal system with a solar collector area of 20 m2 and 0.8 m3 per floor, i.e. 5 m2 and 0.2 m3 per apartment, decreased the use of the electric heater with 44 % while increasing the comfort. Several variations to the system and mode of heating were tested and are detailed in the report. It was found that a solar thermal system has a high potential of heating houses in the Thimphu area. The main obstacle for implementing a solar thermal system is its cost.