Modelling Of An Architecture For Local Energy Generation And Distribution With Peer-To-Peer Electricity Sharing In A South African Context

Abstract

The increasing share of variable renewable energy sources, strict targets set for the reduction of greenhouse gas emissions and the requirements on the improvement of system security and reliability, are calling for important changes in our energy systems. In South Africa, distributed renewable energy systems have emerged as effective ways in improving the quality of energy service. The integration of distributed renewable energy, such as solar photovoltaic systems (PV) and micro-grids, is significantly increasing the coupling and interactions between sources and between supply and end use, at various scales, from multinational, national, and community scale, down to building level. In a South African context, power produced from the renewable energy that is not consumed by the load, needs to be stored for later use, or discarded, as the power utility, as well as the municipalities do not generally allow the power to be sold, or shared through the national grid. In the case where various small generation units residing on the same land (estates or a block of townhouses), the power generated from the PV may be shared between the various consumers on the same land. Consumers on the same land having different load patterns as not everyone uses electricity simultaneously connecting them in a micro-grid may allow the power to flow between the different generation systems and consumers. This will decrease the size of the storage systems, as well as the amount of power dumped and lost when it is not in use. On the other hand, the reliance on the grid power will further decrease. With the increasing installation of distributed generation at the demand side, more and more consumers become prosumers, that may both generate and consume energy. The high penetration of sporadic renewable energy may cause severe problems to power systems. Therefore, in order to facilitate the self-consumption of local generation, the export price at which the prosumers sell electricity to the utility grid is usually designed to be significantly lower than the retail price at which electricity is being purchased. This is the major motivation for prosumers to share excess electrical energy amongst each other, rather than to feed it back to the utility grid at a significantly reduced cost. The decreasing tariff rate of the feed-in tariff in most countries, does make this incentive a significantly more attractive approach. The mathematical modelling of the operation of Peer-to-peer (P2P) energy sharing model between two dissimilar load profiles, will be discussed. These profiles are of typical commercial and residential nature. The P2P system consists of two prosumers: the residential prosumer that has a roof mounted PV system that is fixed at a 30° angle, with energy storage capabilities and commercial prosumer, with a solar tracking system. A description of the system is discussed in detail, with all the relevant components outlined. In order to evaluate the cost effectiveness of the hybrid system, in terms of money spent, a baseline system was established, consisting solely of energy supplied by the grid. The optimal operation of the proposed system was simulated and compared to the baseline system. A life cycle cost (LCC) analysis was conducted for a period of 20 years, for both the baseline and the optimally controlled P2P energy sharing scheme. In addition, two electrical energy storage technologies were evaluated for the proposed system. These technologies include lead acid and lithium ion energy storage configurations. Results from the analysis indicated that, if the system were to use lead acid batteries as a storage medium, the proposed system would break-even in 5.304 years, with an approximate saving of 57%, translating into savings of R 1,972,277.98. The proposed system with Li-ion battery storage, indicated a break-even point of 5.131 years, with an expected saving of 54%, translating into cost savings of approximately R 1,861,939.36 at the end of the evaluated life cycle period. Based on the results from the study, it was observed that the optimally controlled P2P energy sharing scheme has shown to be economically feasible, in the South African context.