Abstract
The growing impact of global warming, environmental pollution from fossil fuel usage, and rising energy demand have heightened interest in renewable energy (RE) sources like solar and wind power. Among available renewable sources, solar photovoltaic (PV) is gaining much interest, due to its gradual technology development and cost reduction. Distributed, grid-connected PV solar power poses a unique set of benefits and challenges. The benefits include, minimizing power losses, increase grid resilience, lower generation costs, and reduce requirements to invest in new utility generation capacity. On the other hand, the integration of large amount of grid connected solar PV systems with intermittent characteristic at the distribution level, bring challenges to the utilities companies regarding the power quality, stability and the reliability of the system. Hence, it is imperative to analyse the impact of distributed solar-PV power generation on the distribution system. This research project focuses on the solar PV integration impacts on the existing distribution network in a research campus in Pretoria, South Africa.
In South Africa, Renewable Energy Independent Power Producer Procurement Program (REIPPPP) has played an important part by facilitating private sector investment into grid-connected renewable energy generation. Furthermore, the load shedding implemented by Eskom also resulted in increased uptake of solar PV systems in the residential and commercial/industrial motivated by the high cost of electricity and need for reliability of supply. In some municipalities, small-scale embedded generation (SSEG) allows households and businesses to feed excess solar PV generated electricity back into the grid, offsetting energy consumption costs. The South African government also offers incentives for businesses investing in renewable energy, including solar PV installations, under the Section 12B tax allowance.
A simulation model was developed using DIgSILENT Power Factory software to investigate and analyse the impacts of integrating solar PV plants into the medium voltage/low voltage (MV/LV) distribution network with different solar PV penetration levels. Solar PV distributed generation impacts several aspects of distribution systems planning and operation, some of the most noticeable effects concern voltage, power quality, protection, technical/power losses, reliability, and operability of the system. These impacts vary in severity as a function of the degree of penetration and location of solar PV distributed generation. A series of scenarios were performed for a typical MV/LV distribution network, to demonstrate the potential solar PV impacts, results were analysed and compared for different operating conditions. The national rationalised specifications (NRS), South Africa grid code and Eskom guidelines were used to evaluate the impacts of solar PV integration on the grid. In each scenario, effects of solar PV plants on the voltage profile, power losses and equipment loading were evaluated. The research study results showed that the level of solar PV penetration up to 50% is acceptable at peak loading, but when solar PV penetration is increased to 75% the network experienced violations. At light loading conditions the network did not experience any violations with higher levels of solar PV penetration (75%).
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The analyses of this research showed that the integration of solar PV plants/units on the existing distribution network have both positive and negative consequences. Introducing solar PV at the load side reduces the load demand on the grid and in turn leads to reduced power losses and improved voltage profiles on the test system. Initially grid power losses decreased as the penetration level increased, but only up to a certain point. Then they began to rise with further increases in PV penetration. The percentage change in losses relative to the initial 0% penetration level calculated for active power were (25%: -2.07% decrease, 50%: +3.84% increase and 75%: +17.30% increase) and reactive power were (25%: -12.19% decrease, 50%: -9.8% decrease and 75%: +7% increase) at peak loading, while at light loading active power losses were (25%: -0.36% decrease, 50%: +0.71% increase and 75%: +3.72% increase) and reactive power losses were (25%: -3.64% decrease, 50%: -3.05% decrease and 75%: +1.73% increase). The integration of solar PV systems also has effect on the loading of the lines (cables) either improve or worsen the system loading.
This dissertation presents the challenges and potential impacts of solar PV integration on the distribution system network. Furthermore, different techniques used to mitigate or alleviate the voltage violation resulting from solar PVs integration in a distribution network were also highlighted. The results of this study can be utilized by municipalities, grid operators, and legislators to aid them in planning, forecasting, and accommodating new solar PV systems in their grids. In future, the study can be extended to include short-circuit analysis, harmonic effect, dynamic studies and grid protection system, or can even be extended by incorporating other forms of technologies such as electric vehicles (EVs) and battery storage.