Design and performance evaluation of an oil/rock bed heat storage system for solar cooking
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Date
2025
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University of Namibia
Abstract
This thesis presents the development and performance evaluation of a sensible thermal
energy storage system that used sunflower oil and rock pebbles as heat storage mediums.
The aim was to assess the system's performance based on charge and discharge rates,
energy storage capacity, power output, cooking efficiency, and cost-effectiveness. The
main body of the system was created with an old hot water geyser. An Arduino-based data
logger was fabricated and was used to monitor and capture temperature changes
throughout system operation periods. The data was analyzed with Python programming,
from which time-temperature graphs were drawn. The heat retention capacity was
obtained by heating the system to about 200 °C and then cooling it, with the time taken to
cool being recorded. The system took approximately 30 hours to cool from 194℃ to 60℃.
The system generated 0.028 kW of power and stored a total of 0.85 𝑘𝑊ℎ of heat energy.
The efficiency testing, which involved boiling five liters of water, yielded an average
efficiency of 78.98%. The total cost of constructing the system was: N$ 3,860, with a unit
energy cost of N$ 1.26/kJ and a unit power cost of N$ 137.86/W. The cooking test
demonstrated that the system could simultaneously cook 300 g of rice in 43 minutes and
300 g of dry beans in about 4 hours using only the stored thermal energy. The study
therefore concluded that the developed system was able to deliver a reliable and cost
effective solution for domestic use. Nonetheless, constraints including insufficient
funding for further development and a limited timescale, impeded comprehensive
investigation of the system's capabilities. Future research needs to improve the design of
the system as well as explore the possibility of using solar PV panels to heat the TES
system
Description
A thesis submitted in partial fulfilment of the requirements for the Degree of Master of Science in Renewable energy
Keywords
Thermal energy storage, Oil/rock bed, Solar cooking, Solar energy, Heat energy, Arduino data logger, Namibia, University of Namibia