OPERATIONAL IMPACT ASSESSMENT OF ROOFTOP SOLAR PV AND BATTERY ENERGY STORAGE INTEGRATION ON A 22 KV URBAN DISTRIBUTION FEEDER IN DA NANG CITY, VIETNAM

The rapid growth of rooftop solar photovoltaic (PV) systems is turning urban distribution feeders from passive, unidirectional circuits into active networks with variable and bidirectional power flows. This paper assesses the operational impact of rooftop PV and battery energy storage systems (BESS) on a real 22 kV urban feeder (outgoing feeder 480 of the 110 kV ADO substation) in Da Nang City, Vietnam. A network model with 17 medium-voltage nodes and 49 monitored 0.4 kV busbars was built in DIgSILENT PowerFactory from utility network data and measured PV and load profiles. Newton–Raphson load-flow studies (11:00, 20:00 and 24-hour profiles) and RMS simulations of cloud-cover and thunderstorm events, with PV represented as constant-power static generators, were carried out for the existing network, for a doubled-PV scenario with distributed BESS and for a load-levelling BESS. With 1.9 MWp of existing rooftop PV (about 16% of the feeder peak) all voltages stay within ±5% of nominal (maximum 1.045 p.u. at the substation bus, 1.026 p.u. at 0.4 kV). The simulated events cause voltage steps of about 0.001 p.u. and short spikes in the local bus-frequency signal (minimum 49.816 Hz; 49.805 Hz with PV doubled); because inverter controls and upstream-grid dynamics are not modelled, this signal is used only as a relative screening indicator and not as a system-frequency result. Doubling the PV capacity to 3.8 MWp with distributed BESS reduces the noon active-power loss by 28% and the daily energy loss by 11.5%. A partial-deployment load-levelling dispatch of 0.62 MW (about 11% of the 5.6 MW / 11.7 MWh design) lowers the evening peak by 5.1%, raises the night valley by 8.1% and cuts active and reactive losses at 20:00 by 21% and 19%; the full design is assessed only economically. A 20-year cash-flow model of the 11.7 MWh BESS gives NPV ≈ VND 113 billion, IRR ≈ 21.8% and a discounted payback of about 6 years under the assumed tariffs, but NPV falls to VND 28 billion if the peak price is 40% lower and to VND 56 billion without tariff escalation, and it is close to zero under combined adverse assumptions, so the economic result is preliminary. The results provide quantitative guidance for utilities planning PV hosting and storage deployment on urban 22 kV feeders.