Preliminary Tests on the Suitability of the Beta PDF to Model the Residential Load for New Planning Applications

The proliferation of distributed energy resources (DERs) such as electric vehicles, photovoltaic systems and battery energy storage systems has increased significantly over the past decade. While the integration of these technologies has several benefits to the grid, a wide spectrum of technical challenges has been reported. The technical challenges are partly due to the fact that the load conditions and operation of the power system with penetration of DERs differ significantly from the conditions accommodated at the time of planning of the network. To host the DERs without violation of quality of supply standards, engineers are facing a new challenge of defining regulations for uptake. Moreover, new planning standards are required for future electrification projects where DER penetration is anticipated. To achieve this, new load models are necessary since the penetration of DERs introduces new periods of strain to the network apart from the interval of maximum demand as previously valid. In South Africa, a probabilistic load flow approach based on the Beta probability density function (PDF) as a descriptor of load currents is the standard for the design of low voltage networks. Since the standard is only applicable to passive feeders without DERs, the associated load models are defined only for the interval of maximum demand. This paper tests the suitability of the Beta PDF to model other intervals relevant for network analysis under DER penetration. Preliminary tests focused on PV applications are presented as a case study. Results demonstrate that the Beta PDF remains a suitable model for the summer after-diversity-demand for grouped customers in South Africa.