Abstract
The purpose of the research was to measure the sustainability contribution of renewable energy sources in the form of Solar Water Heaters (SWH) within low-income household settings of Dimbaza township, South Africa via experimental analysis, statistical tests, survey, and mathematical modelling. Solar water heaters are used as a potential replacement of inefficient electric geyser (electric water heater) to produce sanitary hot water due to the excellent efficiency and the capability of reducing the electrical energy consumption by 50-85%. The study evaluated the performance of a 4 kW electric geyser and a 2 kW input SWH with an auxiliary electric heater (backup element), and quantified the annual energy and cost savings. Electric geyser with the same storage tank capacity (200 L) was used as a reference to compare the performance of the two systems. A data acquisition system was designed and built comprising of power meters, flow meter, temperature sensors, ambient temperature, and relative humidity sensors to monitor the electrical and environmental contributions of the various water heating devices. The hot water set point temperature on each of the technologies was 55 oC. A survey using questionnaires was conducted among the residences in Dimbaza based on the house representative’s perceptions to replace their electric geyser with solar water heaters (based on the monetary saving inscribed on the solar water heaters, the sensitization of the target population on the environmental benefits of the solar water heaters and both the monetary savings and environmental benefits). A multiple linear regression model was developed and validated to predict the energy savings by the SWH system. The model predictions based on the measured and predicted outputs gave high accuracies with over 95% confidence level. The reliefF test was used to rank all the input parameters of the derived multiple linear regression model according to the weights of contribution to the electrical energy saved. The results revealed that the payback time of replacing the electric geyser with the solar water heater with an auxiliary electric heater (backup element) was 3.2 years. The annual energy savings in kWh is 4412.10 and the annual energy savings in Rands is R 8824.24. The life-cost savings to be achieved by replacing the electric water heater with the solar water heater over the period of 20 years would be R 277107,7. The reliefF test revealed that the predictors (ambient temperature and Global irradiance) were secondary factors, while the electrical energy consumed was the primary factor. The findings also depicted that most of the respondents are willing to switch to alternative source of energy such as the SWHs to produce sanitary water heating due to their financial constraints and the high tariff from Eskom and municipality. Conclusively, the research provides substantial evidence for both policy makers
and homeowners to justify the techno-economic and social benefits of retrofitting an electric geyser with a solar water heater.