Use of solar energy to control the environment for aquaponics in low income communities

Abstract

South Africa has one of the rising economies on the African continent, but faces great challenges as to how to reduce its dependency on a coal powered industry, improve outdated agricultural methods, reduce poverty and create awareness of the use of renewable energy amongst low income communities. The research led to the design and development of a prototype Modular Solar Powered Aquaponics System. The system makes use of solar energy such as photovoltaics (PVs) to generate electricity and solar thermal energy to heat the aqueous medium. The use of this renewable energy improves the prototype’s environment, encouraging fauna and flora to flourish for human consumption. The prototype combines an intense vegetable and fish farming production system which has the ability to reduce water and land usage as compared to traditional farming methods. The system successfully yielded a healthy growth of leafy vegetables. Experiments showed that in four weeks’ time, lettuce grew 130 mm, ruby chard 170 mm, spinach 180 mm, rocket 300 mm and cherry tomatoes 515 mm. Lettuce grew particularly quick in this system, where it took 35 days to mature to harvest compared to 50 days when grown by conventional farming methods. The fish growth was carefully monitored and compared to the Von Bertalanffy growth model with results indicating that the growth rate reduced to almost zero after about 400 days, with the fish reaching a mass and a length of about 470 g and 27 cm, respectively, which conforms to the model’s predicted values of mass = 426 g and length = 27 cm. The PV system proved reliable and could sustain the load of 1352 Wh/day for the operation of the aquaponics pump and the four hours of night lights. The energy output from the stand-alone PV system was monitored over an eight-day period during the winter, whereby clear, cloudy and worst-case stormy weather was experienced. An average energy of 1167 Wh/day was recorded for this period. This average slightly underperformed the design criteria of 1352 Wh/day; however, the shortfall was carried by the two days’ autonomy built in the batteries’ storage capacity. The design of the SWH system proved to be adequate during clear sunny days, but lacked capacity during adverse weather conditions (prominent in winter months). It was possible to maintain a temperature close to the required 29° C at the outlet of the collector during ideal weather conditions. Maintaining an average flow rate of 1.78 l/min proved adequate to allow most of the water (~750 l) to pass through the solar collector in one day (~7 hours of sunlight). During winter months, the model predicted a smaller increase in temperature, where the temperature of the water could be raised from 15° C to an average of 19.1° C, with a maximum of 23.4° C just after midday. A pilot system (of which the design is not covered in this thesis) was erected at a low-income community near CPUT: The Africa Community Project (ACP), a non-profit organisation, runs an early childhood development program (ECP) which caters for 125 toddlers, youth and community members. The pilot system currently consists of 4 x 1000 litres capacity fish tanks and a total grow-bed area of 18 m2. In spite of minor difficulties, it has yielded good crop growth and has been accepted as a significant activity by the community. The community supplies crops harvested from the pilot system, such as green and red leaf lettuce, spinach, mint and basis, to a company called Pure Good Food on a monthly basis. This research endeavoured to address the possibility of combining existing with new technologies to empower low-income communities. The research has led to the filing of an SA patent (PA161202P, filed on 17 August 2015).