Design of an energy-efficient renewable energy water purification system with smart metering enhancement

Abstract

South Africa is facing regular water shortages as well as energy shortages. The country is surrounded by two oceans consisting of sufficient seawater to solve its water shortage. However, seawater desalination processes are highly energy intensive. Solving South Africa’s water shortage to the detriment of the energy shortage in the country, is not a sustainable solution. South Africa is also home to an abundance of available solar energy, which places the country in a favourable position to generate energy from the available solar radiation through installing solar Photovoltaic (PV) panels. In order to minimize the amount of energy needed to treat one cubic meter of seawater, an energy efficient water purification plant was designed. The 1 ML/day Seawater Reverse Osmosis (SWRO) plant included smart metering to meter the total energy used from the water purification plant. Flow meters were installed on the plant to keep track of all the treated water and make it possible to calculate energy usage versus produced flow. The designed plant had a theoretical energy usage of 4.79 kWh/m³. Energy saving equipment such as Variable Frequency Drives (VFDs), an Energy Recovery Device (ERD) and smart Programmable Logic Controllers (PLCs) were incorporated to investigate the amount of energy that could be saved. The final average actual energy usage per unit of water was calculated to be 4.07 kWh/m³. This energy value included the complete water purification process from the inlet works until the network distribution of the product water. This value is well within the industry standard of 3 – 6.7 kWh/m³, and is therefore deemed to be efficient. The 0.72 kWh/m³ saving was further determined to be 19 139.76 kWh per month and ultimately, up to 229 677.10 kWh per year. The practicality of powering the 1 ML/day SWRO plant from solar energy was then investigated. The result indicated that 5 x 50 kW three phase inverters would be required to accommodate the total installed power for the water purification plant. This equates to 241 kW in total. To power the water purification plant during the day when the sun is available, 570 PV panels of 545 W each, were required. Ground mounted solar panels would have to be installed in rows within close proximity to the water purification plant. The surface area required was the main contributor in establishing that powering the 1 ML/day SWRO plant from solar energy, would not be practical. The 570 PV panels would need a total area of at least 1725.28 m². This surface area equates to 14 m x 125 m of open land being required, which is suitable for the installation of ground mounted panels. In addition, this area would need to be close to the water purification plant further adding to the impracticality of a solar solution. Blockchain technology in energy could be investigated to trace the origin of the energy feed to the water treatment plant. This technology could therefore be used to ensure that the energy powering the water purification plant originates from a renewable source, should it be required. In this way, the desalination plant can still be powered through renewable energy without the need for the available space within close proximity to the water purification plant.