Batteries: Higher energy density than gasoline?

doi:10.1016/j.enpol.2009.02.030

Energy Policy

Volume 37, Issue 7, July 2009, Pages 2639-2641

https://doi.org/10.1016/j.enpol.2009.02.030 Get rights and content

Abstract

The energy density of batteries is two orders of magnitude below that of liquid fuels. However, this information alone cannot be used to compare batteries to liquid fuels for automobile energy storage media. Because electric motors have a higher energy conversion efficiency and lower mass than combustion engines, they can provide a higher deliverable mechanical energy density than internal combustion for most transportation applications.

Introduction

Policy makers are comparing gasoline alternatives in response to peak oil, pollution, greenhouse gas (GHG) emissions, and foreign energy dependence. Compared to alternatives including biofuels, and hydrogen fuel cell technologies, battery electric vehicles (BEVs) have superior technical viability, performance, existing infrastructure, and efficiency. For instance, the present California grid is capable of charging the majority of the state's cars (if electric) during off peak hours with less cost (Lemoine et al., 2008) and GHG emissions (Unnasch and Browning, 2000) than would powering the same number of cars with gasoline or biofuels.

Yet, electric travel is often dismissed (Borenstein, 2008; Chu, 2008) because the low energy density of batteries (compared to liquid fuels) is inappropriately applied to the mechanical energy needs of vehicles (Fig. 1). Stored potential energy must be transformed into mechanical energy to be of use to the vehicle, and electric motors convert energy many times more efficiently than comparable internal combustion engines (ICEs). Our model¹ compares commercially available (year 2008) electric and ICE vehicles yielding a higher effective energy density for electric vehicles for the majority of daily transportation needs: those not requiring long-range travel without recharge.

Fig. 1 compares the caloric energy densities of energy storage media, the mass energy density² calculated as $ρ_{c} = \frac{U_{f}}{m_{f}},$ where U_f is the stored energy (lower heating value of the fuel or battery energy) and m_f is the mass of the fuel or battery. Battery energy density is smaller than that of liquid fuels by two orders of magnitude. However, the relevant energy is not gross caloric energy stored, but rather net mechanical energy delivered to the wheels, ηU_f, where η is the “stored energy to mechanical work” conversion efficiency and includes contributions from regenerative brakes as well as frictional losses in the transmission. Additionally, a motor and transmission is necessary to convert the stored energy to mechanical work, so the relevant mass should include the drive train mass, m_d: the motor or engine, electrical control and power converters, transmission, exhaust, and all associated parts and fluids. We introduce an effective energy density: $ρ_{E} = \frac{η U_{f}}{m_{f} + m_{d}},$ the ratio of stored energy delivered to the wheels divided by the mass of the fuel and drive train. This effective energy density (Fig. 2) depends on the amount of stored energy on board, which determines the maximum range that the vehicle can drive on one “fill up”. As the driving range is increased from zero (a car with an empty gasoline tank, or no batteries) to infinity, ρ_E increases from zero, asymptotically approaching ηρ_c for infinite range. While this asymptotic value is greater for liquid fuels, effective energy density for shorter ranges is higher for electric storage because of the lower mass of electric motors and drive trains. The “crossover range” (below which electric power systems have a higher energy density than gasoline) for lithium ion batteries is about 120 miles (190 km).

The crossover range varies with automobile. ICE vehicles that are more overpowered (large trucks and sports cars) have heavier engines and lower efficiency resulting in a crossover range of greater distance. Economy and hybrid cars (see Fig. 3) both have crossover ranges between 70 miles (115 km) and 80 miles (130 km). Hybrids have a greater efficiency than regular economy cars, but have a slightly lower effective energy density due to the extra mass of carrying both an ICE and electric motor.

Increasing range presents no challenge for ICE travel, amounting to increasing the size of the gas tank. However, increasing the range of the BEVs requires more batteries, considerably increasing mass. Conversely, lowering range allows the BEV to have a greater energy to mass ratio compared to ICEs. Fig. 4 indicates that even the lower crossover range of the economy cars exceeds the needs of the vast majority of American trips—especially if this range is for one-way transportation, possible with charging capability away from home (Fig. 5).

Section snippets

Methodology

We compared similar vehicles (see footnote 1): The Tesla Roadster (BEV) is compared to the Lotus Elise (ICE). These two sports cars have nearly identical bodies and performance. The Ebox (BEV), Scion (ICE), and Prius (hybrid), were compared for economy vehicles. The Ebox is made by retrofitting a Scion with an electric motor, so these two vehicles are mechanically identical. The Prius is somewhat different, but has similar performance and drag coefficient to the Scion and Ebox.

Because

Power density qualification

Arbitrarily short-range electric vehicles are not possible because of the limited Li ion battery power density of about 1 kW/kg. The power requirements for the Tesla Roadster require a 200 kg battery, or a minimum range of 125 km (80 miles). Additionally, in a low state of charge, the battery experiences enhanced degradation under maximum power load, which can be prevented by reducing delivered engine power when the battery is in a low state of charge. Both the Tesla and Ebox have extremely high

Discussion

In the technical and societal transition we have begun, we have the opportunity to rethink how we use energy, and in particular how we use energy for transportation. Present ICE vehicles are the standard each new technology is judged against. If a new technology presents an added inconvenience (such as shorter range), it is found untenable. However, ICE-related inconveniences (oil changes, visits to the gas station, higher probability of breakdown, etc.) are accepted as given. Moreover, ground

Acknowledgements

Acknowledgement is made to the Donors of the American Chemical Society Petroleum Research Fund and Department of the Navy, Office of Naval Research, under Award # N00014-06-1-1111, for partial support of this research.

References (6)

Borenstein, 2008. Cost, Conflict and Climate: US Challenges in the World Oil Market. In: Borenstein, S. (Ed.), Center...
A. Chu
American physical society physics of sustainable energy at UC, Berkeley, March 1–2, 2008 opening talk by Steve Chu, director of Lawrence Berkeley National Laboratory; associated paper: (Chu, S., Chapter 1, Science of Photons to Fuels)
DOT, 2003. Source: DOT OmniStats, Vol. 3(4) October...

There are more references available in the full text version of this article.

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