The challenge of meeting the Corporate Average Fuel Economy (CAFE) standards of 2025 has resulted in the development of systems that utilize alternative energy propulsion technologies. To date, the use of solar energy as an auxiliary energy source of on-board fuel has not been extensively investigated, however. The authors investigated the design parameters and techno-economic impacts within a solar photovoltaic (PV) system for use as an on-board auxiliary power source for the internal combustion engine (ICE) vehicles and plug-in electric vehicles (EVs). The objective is to optimize, by hybridizing, the conventional energy propulsion systems via solar energy based electric propulsion system by means of the on-board PVs system.
This study is novel in that the authors investigated the design parameters of the on-board PV system for optimum well-to-tank energy efficiency. The following design parameters were analyzed: the PV device, the geographical solar location, thermal and electrical performances, energy storage, angling on the vehicle surface, mounting configuration and the effect on aerodynamics. A general well-to-tank form was derived for use in any other PV type, PV efficiency value, or installation location. The authors also analyzed the techno-economic value of adding the on-board PVs for ICE vehicles and for plug-in EVs considering the entire Powertrain component lifetime of the current and the projected price scenarios per vehicle lifetime, and driving by solar energy cost ($ per mile). Different driving scenarios were used to represent the driving conditions in all the U.S states at any time, with different vehicles analyzed using different cost scenarios to derive a greater understanding of the usefulness and the challenges inherent in using on-board PV solar technologies.
The addition of on-board PVs to cover only 1.0 m2 of vehicle surfaces was found to extend the daily driving range to up to 2 miles for typical 2016 model vehicles, depending upon on vehicle specifications and destination, however over 7.0 miles with the use of extremely lightweight and aerodynamically efficient vehicles in a sunny location. The authors also estimated the maximum possible PV installation area via a unique relationship between the vehicle footprint and the projected horizontal vehicle surface area for different vehicles of varying sizes. It was determined that up to 50% of total daily miles traveled by an average U.S. person could be driven by solar energy, with the simple addition of on-board PVs to cover less than 50% (3.25 m2) of the projected horizontal surface area of a typical mid-size vehicle (e.g., Nissan Leaf or Mitsubishi i-MiEV). Specifically, the addition of the proposed PV module to a 2016 Tesla Model S AWD-70D vehicle in San Diego, CA extended the average daily range to 5.2 miles in that city. Similarly, for the 2016 BMW i3 BEV in Texas, Phoenix, and North Carolina, the range was extended to more than 7.0 miles in those states.
The cost of hybridizing a solar technology into a vehicle was also estimated for current and projected prices. The results show for current price scenario, the expense of powering an ICE vehicle within a certain range with only solar energy was between 4 to 23 cents per mile depending upon the vehicle specification and driving location. Future price scenarios determined the driving cost is an optimum of 17 cents per mile. However, the addition of a PV system to an EV improved the economics of the system because of the presence of the standard battery and electric motor components. For any vehicle in any assumed location, the driving cost was found to be less than 6.0 cents per mile even in the current price scenario.
The results of this dynamic model are applicable for determining the on-board PV contribution for any vehicle size with different powertrain configurations. Specifically, the proposed work provides a method that designers may use during the conceptual design stage to facilitate the deployment of an alternative energy propulsion system toward future mobility.
Design and In-orbit Demonstration of REGULUS, an Iodine electric propulsion system
