Efficiencies and Operating Costs Comparisons

A car is simply an energy consuming appliance that performs a useful function. Like any other appliance, such as a washer, a dryer, or a furnace, the efficiency it operates at plays a significant factor in its overall cost of operation, and in the effect it has on the environment. The less energy used to perform an equivalent task, the better.

Take for example a geothermal heat pump. In Manitoba, a heat pump has two important advantages. First it operates on renewable electricity instead of fossil fuels; then it goes one step further and consumes far less energy than a conventional furnace. Even though a heat pump costs far more than a conventional furnace, this difference is eventually surpassed through lower energy costs due to its higher efficiency. The same principles hold true for a plug-in battery powered electric automobile drive system, such as that used in a PHEV.

Because a PHEV has both a battery powered electric motor and a gasoline engine, the two drivetrains will be discussed separately below. The greater the electric range, the more the efficiency and fuel costs of a PHEV will behave like an electric car and the less they will behave like a gasoline car. A PHEV-30 (30 mile electric range) will run about 50% each on electricity and gasoline.

Battery efficiency

A battery is typically four times as efficient as gasoline or hydrogen at storing energy for vehicle motion. While hydrogen is often touted in the popular media as the “fuel of the future” and hydrogen fuel cells are often claimed to be more efficient than gasoline engines, scientific literature is less optimistic. Hydrogen unfortunately suffers from the unavoidable necessity to manufacture it from other forms of energy, such as gasoline, natural gas, and electricity, losing a significant portion of potentially useful energy in the form of heat.

The hypothetical advantage of fuel cells is quickly lost in a complex chain of water pumps, electrolyzers, reformers, hydrogen compressors, piping, storage tanks, air compressors, ice management systems, radiators, and so on. These are needed to manufacture the hydrogen from other sources of energy, deliver it to the vehicle, and process the waste — water — which is tricky in winter. Freezing may damage a fuel cell. Fuel cells that have been designed to operate in milder winter conditions typically lose several miles worth of fuel consumption just to sit still while warming up to operating temperature. The platinum filled plastic fuel cell membrane needs to be moist to operate.

Batteries, particularly newer designs, can operate directly on renewable electricity — even in winter — releasing it when needed with over 90% energy efficiency. Present day battery efficiency is far beyond the physical limits of any present or proposed fuel cell, with or without the rest of the complex hydrogen machinery chain. Higher efficiency directly translates into lower cost and a lower effect on the environment — one quarter the impact.

Proponents of hydrogen fuel cite PHEV technology as an introductory technology for hydrogen fuel cells. In theory, PHEV technology, using a fuel cell instead of a gasoline engine, can lower the cost and weight of a hydrogen fuel cell vehicle by replacing part of the demand on the fuel cell system with batteries charged off an electrical outlet. A hydrogen fuel cell PHEV-30 (with 30 mile battery range) would use half the hydrogen, have about double the electrical efficiency of a hydrogen fuel cell vehicle (because the battery is four times as efficient), and significantly reduce the need for finding hydrogen fuelling stations. This is a significant improvement over a 100% hydrogen powered vehicle, but a 100% battery electric vehicle would still be about twice as efficient as a hydrogen fuel cell PHEV.

Cost comparison

The following table reflects the effects of energy efficiency on the relative fuel costs of operating similarly sized vehicles in Manitoba. The conventional hybrid electric vehicle (HEV) operates 100% on gasoline, generating all of its electricity on-board. Currently there are no road taxes assessed on electricity or hydrogen comparable to gasoline. The cheapest sources of hydrogen are natural gas and coal in chemical processes, followed by a nuclear thermal process. Hydrogen made from electricity is not included, but is approximately double the cost of manufacture from natural gas.

Disadvantage of battery drive systems

The most significant physical disadvantage of a battery electric drivetrain is the inability to recharge quickly, but even this is changing. Rapid recharge batteries are beginning to show up in the marketplace that can be fully recharged in one to fifteen minutes. Even without these batteries, PHEV is a formidable practical challenger to gasoline because it shares some of the same technology and the same fuelling infrastructure. A hydrogen fuelling infrastructure does not yet exist, and the development of one will be long and very expensive.

Other Emerging energy storage technologies

There is a wide variety of other emerging energy storage technologies that may also prove useful in transportation or other uses some day. This includes:

• fuel cells that do not depend on hydrogen, such as higher temperature ones that can operate directly on methane or other hydrocarbons, including biogas and other biofuels;
• fuel cells that operate on metal fuels (reversible with electrolysis);
• fuel cells that operate reversibly on flowing electrolytes (very fast acting like batteries);
• other fuel cells which are far more experimental;
• other options such as capacitors, flywheels, compressed air, and thermal storage.

Other factors affecting efficiency and operating costs, which must be controlled for a fair comparison, are:

• driving habits;
• vehicle size;
• weather;
• tire inflation.