Saving Petroleum with Cost-Effective Hybrids

Trade-offs between fuel economy improvement, and thus petroleum savings, and economic factors, such as vehicle cost differential and break-even gasoline price, are studied for mild (15% of total driveline power electric) and full (engine and electric power are about equal) hybrid vehicles. The study considered compact and mid-size passenger cars and mid-size SUVs. The same weights and road loads were used for the conventional ICE and hybrid vehicles. It was found that the fractional fuel savings are greater for the full hybrids (40-50%) than for the mild hybrids (30-40%). However, the break-even gasoline prices for the mild hybrids are significantly lower than that for the full hybrids. In the cases of the mild hybrids using conventional PFI gasoline engines, the break-even gasoline prices were found to be $1.25-1.50/gal for a vehicle use of 100,000 miles over 8 years and a discount rate of 4%. For the full hybrids, the corresponding break-even gasoline prices were $2.00-2.30/gal.

An EXCEL spreadsheet economic model was developed in which the cost input and economic factors could easily be changed by the user. This was done because the results obtained in the study are highly dependent on the cost and economic factors assumed. The primary objective of the study was to show the trade-offs between potential petroleum savings and economic attractiveness for different hybrid vehicle design options (mild and full) for a reasonable set of inputs. The fuel economy and break-even gasoline price trends for the two hybrid designs are more meaningful than the absolute numerical values obtained.