Adaptive scheme for improvement of load factor of water heater loads in residential buildings

Abstract

The South African power utility, Eskom, and, in turn, the metropolitan and local municipalities, have difficulty meeting the country's growing demand for electricity. In this study, electric water heaters have been identified as the appliances consuming the most energy in residential buildings. There are periods when the demand for electricity is very high across the power system, specifically in the mornings and evenings during winter from May to August, when consumers’ need for electricity, for lighting, cooking, and heating water, peaks. Methods are constantly being sought to assist Eskom and municipalities with network constraints and overloading during periods of high demand, as well as to assist consumers in reducing their electricity costs. Overloading the power system can result in power outages and blackouts and damage to equipment. These challenges can be prevented by introducing load management systems, also known as Demand Side Management, to balance the supply of electricity on the network. This is a method of controlling the load to meet the demand, thereby reducing peak loads, and maintaining and protecting power system stability. Constant upgrading of power plants and primary and secondary substations is needed to meet the growing peak demand, but, alongside this, measures to save electricity must constantly be explored. This dissertation examines ripple control as a load management tool to shift the energy demand of electric water heaters in residential buildings from periods of high demand for electricity to off-peak periods. Ripple control enables the power utility to switch off the electric water heaters of a group of consumers simultaneously, to prevent high demand during peak hours overloading the power system. This could assist municipalities with network constraints and provide considerable savings to the consumer. This method has been successfully used throughout South Africa by Eskom and municipalities. A dynamic of control load model of ripple controller was used in this research, to obtain real-time load measurements on the consumption pattern of electric water heaters. The Rietvlei substation is supplied with 400 kV from Eskom transmission lines and stepped down to 132 kV. Data to measure the load was collected from the City of Tshwane Municipality’s Eskom meter connected inside the Rietvlei substation. The ripple control v telegram was injected into the medium voltage busbars in the substation and propagated down to the low voltage networks throughout the distribution area, where receivers picked up the signal and switched loads or tariffs, as indicated in the study conducted. The results confirmed the effectiveness of the ripple controller for load shifting and load factor improvement during high peak demand. A capacity test indicated that Centurion has 8 000 receivers to operate. Based on 8 000 receivers, the annual saving on the municipality’s Eskom account is over R 11 592 000 per year at today’s tariff. This provides evidence that the application of such a system is essential. The prime objective of a Load Control scheme is to do energy shifting and avoid demand peaks.