Experimental Analysis of a 200 Litre Underground Thermal Storage Reservoir for Solar Water Heater System

Abstract

Abstract

The technology for Solar Water Heating Systems (SWHS) is an on-going innovation. Over the years, various models of SWHS have been developed for various industrial and domestic thermal applications. Despite the wide range benefit of solar energy, its intermittent nature is a major drawback. Hence, a proper thermal storage system will in doubt, enhance the maximization of solar system. The paper seeks to explore the concept of underground thermal storage tank system for the purpose of increasing the thermal storage duration of SWHS to meet daily hot water demand during night hours and during overcast. A laboratory pre-testing of the temperature retention capacity of thermal storage tank without any form of lagging shows an average temperature loss of 3⁰C per hour and an average temperature loss of 1⁰C per hour, when it was partially lagged (with only polystyrene). A five months (May 2021 to September, 2021) experimental investigation of a 200 litre/day solar water heater with an underground thermal storage system installed at Good Pasture Clinic and Maternity, located at N0-6 Citta Avenue, No-Mans-Land,, Kano, Nigeria, is presented. The experimental setup of the system comprises an overhead cold water storage tank, circulation pump, two collectors (a flat plate collector and an evacuated collector), a 200 litres underground thermal storage tank and a temperature data logger with temperature probes. A five months (May, 2021 to September, 2021) experimental investigation of the underground thermal storage tank shows that it took five months for the temperature of water of about 42⁰C to fall to about 28⁰C. The first two months recorded a temperature drop in the water of about 3⁰C, while the third month recorded about 7⁰C drop in water temperature. A sort of thermal equilibrium was reached with temperature of water fluctuating around 29⁰C and 28⁰C in the fourth and fifth months of the experiment. The result further confirms the usability of the underground thermal storage tank as a thermal storage candidate for solar water heater system.

Key Words: Renewable, Solar, Intermittent, Underground, Seasonal and Temperature.