Impact of solar photovoltaics on the system stability of the Zambia national grid

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Phiri, David.C.
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The University of Zambia
The use of renewable energy sources is one of the crucial components of the contemporary issues of sustainable development. Sustainable energy development gives a rationale to have resources that are economical, environmentally friendly and whose social effects are acceptable. However, the potential for a large-scale shift from the use of conventional fuels to renewable energy for electricity generation remains a highly debated issue especially in developing countries. The major argument is that large-scale implementation of renewable energy poses significant challenges to legacy power systems due to temporal fluctuations, geographical dispersion of renewable energy resources and the presumed inadequacy of the existing power grids which are still dependent on traditional power generation technologies. In this study, the impacts of integrating Solar PV power generation on an existing grid were investigated. The investigations were performed by modelling and simulations in power system software (DIgSILENT PowerFactory). The highlights of the investigation results are that there was alteration of voltage levels, changes of line losses, reversal of power flows and improvement in steady state voltage stability depending on level of penetration of Solar PV and the operating condition of the given injection point. The study concluded that a loss of Solar PV power generation had more adverse effects than a startup of such a power plant. Further, the study concluded that changes in solar irradiance may not result in adverse impacts on the stability of the grid provided that the generation is within the limits for which the grid is capable of handling a total loss of generation. For the Zambian grid, the study concluded that with a non-cumulative scenario, up to 123 MW at Leopards Hill and 121 MW at Lusaka West Substations of Solar PV could be injected into the 132 kV busbars resulting in additional loading of about 25.5 % and 31.5 % on the respective busbars, without adverse effects. However, an uncontrolled loss of generation for the 123 MW and 121 MW Solar PV power at Leopards Hill and Lusaka West would result in a total system failure for each non-cumulative scenario. System stability could be achieved for a total loss of generation of 43.6 MW of Solar PV generation at the Leopards Hill and Lusaka West resulting in additional loading of about 9.2 % and 11.5 % as a maximum on the respective busbars, thereafter reinforcements on the national grid may be necessary. Arising from the study the Kabwe Pensulo line was identified as a weak link therefore lending itself to further investigation for a Solar PV power plant at the Pensulo Substation. It was found that a maximum of 130 MW could be injected on to the 66 kV Pensulo Busbar but only 49.5 MW Solar PV generation on the 66 kV busbar at Pensulo could retained system stability after total loss of generation, resulting in 240 % maximum additional loading but only 51.3 % additional loading on the 66 kV bus bar could yield system stability after total loss of generation. In view of the need to diversify from hydroelectricity power generation which is highly susceptible to hydrological fluctuations, the study recommended the scaling up of Solar PV power generation through the modification of legislation and associated regulations and codes that were developed for conventional power generation so as to enable flexibility in the design, construction and operations of future power (generation and Transmission) infrastructure. Keywords: Power System Stability, Renewable Energy, Solar Photovoltaic, Utility Scale, Integration, National Grid, PowerFactory DIgSILENT
Renewable energy sources. , Renewable energy.