Optimal Power and Energy Modeling and Range Evaluation of a Solar Assist Plug-in Hybrid Electric Tractor (SAPHT)
Environmental problems associated with burning of fossil fuel and the medium-term and long-term supply of fossil fuel itself, particularly oil, make the move toward a global renewable energy economy both desirable and necessary. Considering these constraints, the SAPHT (Solar Assist Plug-in Hybrid Electric Tractor) was designed, constructed, and evaluated for a farm's light-duty applications. Approximately 18% of the energy consumed daily by the SAPHT is supplied by an onboard photovoltaic (PV) array, and the rest is supplied via an electricity grid. In this research, after optimal power and energy modeling, six standard agricultural implements were attached to the SAPHT in order to determine the operating range of each implement. Field test data illustrated that with a 16.5 kWh valve-regulated lead acid (VRLA) battery pack, it was possible to operate a single-bottom moldboard plow and a two-row planter for 4 h, and a standard mower, sprayer, and fertilizer for 3.2 h, 3.6 h, and 3.4 h per day, respectively. In addition, using this battery pack, it was possible to pull a two-ton weighted trailer for 2 h on asphalt with a velocity of 25 km h -1 , for 2.5 h on a sand road at 18 km h -1 , and for 3 h in a field at 9 km h -1 . More operating hours would be available with the use of batteries with higher energy densities at the same weight.