The weight of a plug-in hybrid electric vehicle (PHEV) battery significantly affects its electric driving range, with both positive and negative implications:
- Increased Battery Weight for More Energy Storage: Larger batteries with greater weight can store more electrical energy, which directly increases the electric-only range (all-electric range, AER) that a PHEV can travel on electricity before switching to gasoline. For example, PHEV batteries designed for about 20 miles of EV-mode travel are comparatively lighter and offer a balance between electric range and efficiency, whereas batteries targeted for a 40-mile EV range are heavier but provide extended electric driving capability.
- Efficiency Tradeoff Due to Added Weight: While a bigger battery allows longer electric travel, the additional battery weight reduces the vehicle’s overall energy efficiency. This is because the heavier vehicle requires more energy to move, which decreases miles per kWh in electric mode and miles per gallon when running on gasoline after the battery is depleted. The vehicle carries the full battery weight throughout the trip, even after the battery is exhausted, unlike gasoline which becomes lighter as fuel is burned.
- Typical Battery Weights and Energy Density: PHEV and EV batteries vary widely in weight depending on capacity; for example, batteries storing 6 to 12 kWh might weigh between 100 and 150 kg, while larger batteries around 40 kWh or more can weigh 300 kg or more. Generally, heavier batteries correlate with higher energy capacity but also necessitate structural support, adding more weight to the vehicle.
- Energy Density Improvements Mitigate Weight Impact: Advances in battery energy density (energy stored per unit weight) help reduce the penalty of added weight. For instance, newer Li-ion battery packs target energy densities around 140 Wh/kg compared to older packs at about 46 Wh/kg, allowing more energy storage with less weight increase, thereby improving electric range without proportionally increasing the weight burden.
In summary, PHEV battery weight contributes positively to electric range by increasing stored energy but negatively impacts range efficiency due to the additional load on the vehicle. Optimal battery sizing balances these factors, considering typical daily driving distances and charging behavior to minimize fuel use and emissions while maintaining practical vehicle performance.
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