Physical Model Simulations of Solar Thermal Energy Storage in Basaltic Rock Fills

Abstract

The efficiency of solar thermal energy storage system using basaltic rock fills has been assessed using a scaled-down model.  The proposed system is designed to operate without external electricity, as it is intended for poor people in remote and severely cold areas.  During the daytime the solar energy is collected and stored in basalt ballasts filled in a shallow pit excavated above groundwater table.  The surrounding soil and acrylic sheet cover serve as insulator.  The stored thermal energy is released to warm up housing through a system of tubing at night.  The thermal properties of ten rock types that are widely exposed in the north and northeast of Thailand are determined in the laboratory.  A scaled-down model simulating the storage system and housing is constructed to monitor the temperature changes at various system components.  Mathematical models are derived to compare with the monitoring results.  Burirum basalt has been selected for testing as it poses the highest thermal conductivity and specific heat.  The results indicate that throughout the night the system can increase the housing temperature by 4 to 6 Celsius higher than that of the surrounding, depending on the packing density, tube sizes and surrounding temperatures. The efficiency of this storage system is about 35 percents. The gained heat energy in the housing is equivalent to the electrical energy of 203.3 kJ×hr.  The mathematical models developed here agree well with the measurement results.