The Argonne National Laboratory has completed its study into the impact of real world drive cycles on the fuel efficiency and cost of different plug-in hybrid electric vehicles (PHEV), with mixed results.
It found that while all PHEV demonstrated potential, the benefits of adding more battery capacity appeared to decrease as the pack size increased.
The Argonne team modelled four PHEV configurations: an input power split with a fixed ratio between the electric machine and the transmission PHEV with a 4kWh and an 8kWh pack; as well as a series hybrid with a 12kWh and a 16kWh pack. These were compared to a conventional hybrid electric vehicle, as well as a conventional combustion engine.
A basic comparison of fuel consumption produced mean values of:
Basic conventional: 6.6l/100km (35.6mpg US)
Hybrid (HEV): 4.69l/100km (50.2mpg US)
Split 4 kWh: 3.27l/100km (71.9mpg US)
Split 8 kWh: 2.32l/100km (101.4mpg US)
Series 12 kWh: 1.50l/100km (156.8mpg US)
Series 16 kWh: 1.23l/100km (191.2mpg US)
As these result show, the larger the battery, the more fuel saved – however, the delta for consumption is not linear. The fuel saved by going from four to eight kWh is much greater than the fuel saved going from 12 to 16.
In addition to the significant gain made from going from a conventional vehicle to a hybrid, the 4kWh configurations offered an additional 20 per cent increase.
Based on these results Argonne concluded that hybrids are more cost effective than the split 4kWh for driving longer than 30 miles but the order is reversed over shorter distances. When driving long distances both series configurations achieve similar payback as the additional battery cost is offset by fuel efficiency benefits.
