Performance Characterization of a Standalone Solar-Photovoltaic Powered Cassava Grating System for Off-Grid Rural Applications

In rural Nigeria, mechanized cassava processing is still a challenge because of unreliable grid electricity and expensive petroleum fuels. Critical analysis of previous studies shows that although the individual elements, such as solar-powered agricultural machinery, cassava grating machine mechanical design, and variable speed motor control, have been studied separately, a system-level characterization of a solar-PV and battery powered cassava grating machine with a variable-speed-capable drive has not been adequately reported. This paper presents the design, construction and preliminary performance characterization of a solar-photovoltaic (PV) powered cassava grating machine. The system uses a 1.5 kW DC motor running on 12 VDC, powered by a 200 Ah deep-cycle gel battery. The battery is charged by two 320 Wp monocrystalline PV modules through a 60 A PWM charge controller. The grating assembly is made of a mild steel drum (350 mm diameter, 100 mm length) with a perforated stainless steel grating surface. Performance was assessed using mass recovery efficiency (mass of grated pulp collected divided by mass of peeled cassava fed, in %), battery-only run time, recharge time and energy balance. In four replicate trials at each of three batch sizes (2.00, 3.80 and 4.00 kg; 12 trials in total), the mean mass recovery efficiency was 95.01% (sample standard deviation 1.08 percentage points). In single battery-only tests, the run time was 115 minutes for soft cassava at low speed and 86 minutes for firm cassava at high speed. Recharging the battery after operation (stated depth of discharge about 50%) took 3 hours and 45 minutes at a measured mean PV output of 520 W. The results indicate that the prototype can operate from solar-charged battery storage under the tested conditions.