Evaluating the performance of solar water heaters in Nairobi County, Kenya

Abstract

Kenya is endowed with ample solar energy resources, with annual averages over 5 kWh/m2/day available throughout the country. Solar domestic water heating technology has become a common application in many countries and is widely used for heating in single or small multi-family homes. During peak periods that is in the mornings and evenings most of electricity is consumed leading to overload. Much of this electricity is used in water heating and cooking. In order to reduce on this consumption then solar water heating has to be used to cater for electricity that could otherwise be used in water heating.The main objective of the study was to evaluate the performance of solar water heating in Nairobi Kenya, the specific objectives are to determine the effect of tilt angle or orientation and collector size on the thermal performance of solar water heaters, to evaluate the effectiveness of the existing solar water heaters and to determine the cost benefit analysis of installed systems. Infrared thermometer was used to measure temperature, Hukseflux pyranometer for insolation measurement and Thermal solar software for analysis of the performance. This study was conducted between May and June and the temperatures were measured between 9.00 and 16.00 hours. For Flat Plate Collectors, the highest temperatures were attained at 2.00 pm and it gave an average temperature of 670C and the lowest temperature was at 9.00 am and it gave temperatures of 420C for a collector area of 4.6m2 and orientation of 450. For a collector area of 2.9m2 and orientation of 320, the highest temperatures was 500C at 2.00 pm while the lowest was 26.50Cat 9.00 am. ETC’s gave the highest average temperature of 900Cwhich was attained at 2.00pm and the lowest was 79.50C at 9.00 am for a collector area of 6.9m2 and collector orientation of 400. For a collector area of 2.9m2 and orientation of 300, the highest average temperature was 680Cwhich was attained at 2.00pm and the lowest was 30.40C at 9.00 am.The highest solar insolation attained was 6.5kWh/m2/day and the lowest was 3.76kWh/m2/day in May and in June the highest was 6.1kWh/m2/day and lowest was 3.78kWh/m2/day. During this study T*SOL software was used to simulation and analysis of annual thermal performance of both FPC and ETC and it gives an overview of operation of these collectors throughout the year.Cost benefit analysis of the SWH systems were done at a price per kWh of KES 12.75 for a consumption of 50 to 1500kWh for May to September 2017. FPC gave payback period of 2 years and changing the price for ETC gave a payback period of 4 years. It is recommended that angles of 450 for FPC’s and collector area of 4.6m2 be considered while ETC’s optimum angles recommended is 400 collector area of 6.9m2.