Techno-economic analysis of innovative production and application of solar thermal chilled water for agricultural soil cooling

Abstract

Tropical climate countries are net importers of temperate crops due to difficulties encountered in cultivating them, thus constant increase in prices of these crops is always experienced due to increasing demand. To meet the demands, efforts have been made to adapt temperate crops to tropical climate but the crops quality is always low even though at high production cost. Cool greenhouse or upland farming has been deployed in some cases but these are respectively energy consuming and detrimental to mountain ecosystems. Soil cooling is considered to be appropriate in this case to create winter-like soil temperature and to reduce soil water evaporation. Sustainable chilled water production from solar thermal combined power and cooling is presented in this paper to use the (virtually) free solar energy in the tropics to run a combined plant of organic Rankine power and vapour absorption refrigeration cycle thereby generating electrical power together with chilled water production. The study involves the analysis of a sample size soil in Malaysia to determine its cooling load and the plant capacity to overcome the load. The technical analysis is based on the performance of the combined plan over a range of working fluid superheating temperature and the effective solar collector size to supply the needed heat at the range of the temperatures. The economic analysis is carried out (using RETScreen software) by comparing all the associated costs of the present case (using solar energy) with a based case (using power from the national grid) over a 20-year plant life. Analysis shows that 3.5 kW plant size of the present case has a simple payback time of 14.2 years, while 7.0 kW plant size gives simple payback time of 10.8 years. The sensitivity shows that change in investment cost has more influence on viability of the system than electricity cost