Implications of temporally and geographically realized energy use for electrified transportation

Abstract

Plug in electric vehicles (PEVs) are vehicles that use energy from the electric grid to provide tractive and accessory power to the vehicle. The nonexistent (electric vehicles) or reduced-sized (plug in hybrid vehicles) engine in these vehicles results in high energy conversion efficiencies, lower GHG emissions, and reduced environmental pollution. Consumer demand for these vehicles is limited by their reduced range relative to conventional vehicles. Range limitations in PEVs are primarily due to the lower onboard energy storage capacity of lithium ion (720kJ/kg) relative to gasoline (47.2MJ/kg), and the range sensitivity of PEVs to accessory loads, primarily cabin conditioning loads, is higher. The factors such as local ambient temperature, local solar radiation, length of the trip and thermal soak have been identified to affect the cabin conditioning power requirements and to therefore affect vehicle range. The steady increase in consumer demand for PEVs has resulted in research initiatives by USDOE, the automotive industry and utility industry to overcome these range limitations. The focus of this research is to develop a detailed systems-level approach to connect HVAC technologies and usage conditions to social, environmental, and consumer-centric metrics of performance. This is accomplished through the development of a toolset that consider transient environmental parameters, real world driver behavior, charging behavior, and regional passenger fleet population for HVAC system operation. The resulting engineering toolset can be used to determine geographical distribution of energy consumption by HVAC systems in electric vehicles, identify regions of US where EVs can elicit positive user response, evaluate the sensitivity of PEV range to the local weather conditions, identify times of use to extract maximum performance from PEVs, establish HVAC component specifications, and optimize vehicle energy management strategies and technologies. A case study with the alternative accessory technology such as a combination of phase change materials to provide for heating and cooling is explored. The results of this research show that PEV HVAC energy consumption is geographically and temporally disparate, that range variability may be more of a driver of consumer dissatisfaction than actual range, and that HVAC energy management and technologies can reduce the variability in PEV range and may thereby improve PEV consumer acceptability.