Rolling-horizon optimization of grid-tied PV–BESS for tariff savings, apparent-demand reduction, and critical-load survivability: A Tanzanian university case study

This work presents a measurement-based techno-economic and reliability framework for sizing and dispatching a behind-the-meter photovoltaic and battery energy storage system (PV–BESS) at Mbeya University of Science and Technology (MUST), Tanzania. The analysis uses 26,280 measured, audited, timestamp-synchronized 20-minute active/reactive load data. The PV-generation profile was derived from historical global horizontal irradiance (GHI) time-series data using a validated PV system simulation framework, then synchronized with the measured demand series. Reliability is assessed using a 50-event outage calendar compiled from verified TANESCO interruption records and cross-validated with campus facility logs. Among retained candidates, only one design satisfies both planning constraints: 400 kWp PV, a 100-kWh BESS, and a 50-kW bidirectional converter operated with a 40% reserve state of charge. Relative to the grid-only case, this design reduces grid purchases by 51.96%, annual maximum apparent demand by 14.49%, and the annual tariff bill by 48.25%. It yields an NPV of TZS 150.58 million, an internal rate of return of 9.57%, and a simple payback of 9.13 years. It achieves 99.87% two-hour survivability and supplies 99.49% of modeled critical energy in the outage-calendar replay. Overall, PV delivers most of the energy and tariff benefit, whereas the BESS is retained primarily for outage readiness; this distinction matters when interpreting the constrained optimum.