The Utilisation of Hybrid Systems for Addressing Low Power Generation Issues during Hot Seasons in Micro Hydro Systems. A Case Study from Kitai Prison Complex, Ruvuma, Tanzania

Seasonal variation in streamflow is a major technical constraint for run-of-river micro-hydropower systems supplying rural and institutional loads. This paper presents a refined assessment and optimisation of a solar photovoltaic (PV)-micro-hydropower hybrid system for Kitai Prisons Complex in Mbinga District, Ruvuma Region, Tanzania. The study combined an appliance-based load survey, field hydrological measurements, solar-resource assessment, HOMER Pro optimisation, and MATLAB/Simulink validation. The assessed electrical demand of the complex was 23.79 kW peak and 175.74 kWh/day. Re-analysis of ten seasonal discharge measurements gave a rainy-season mean flow of 0.471 m³/s and a dry-season mean flow of 0.198 m³/s, while 0.336 m³/s was retained as the representative average design flow. At a corrected design head of 9.1 m and an overall efficiency of 0.80, the corresponding hydropower outputs were approximately 33.62 kW in the rainy season, 23.99 kW at the representative average flow, and 14.15 kW in the dry season. Extremely low-flow sensitivity values of 0.149-0.159 m³/s reduced hydropower output to about 10.65-11.36 kW, confirming the need for PV and storage support during critical dry-season periods. The site's solar resource is favourable, with monthly daily radiation ranging from 5.7 to 6.9 kWh/m²/day and an annual mean of about 6.11 kWh/m²/day. A 19.5 kW PV array, 160 kWh battery energy storage system, and 5.5 kW solar-assisted pump were therefore integrated with the micro-hydro plant. The optimised HOMER configuration achieved a net present cost of approximately USD 151,386, a cost of energy of USD 0.183/kWh, and a 100% renewable fraction under the modelled case. The results show that hydro-PV hybridisation with battery storage and controlled pumping can eliminate dry-season peak deficits and improve energy reliability for institutional electrification in Tanzania.