Now, two years later after crude oil price peeked and then stabilized amidst the economic turmoil, the main reason for companies from Toyota and GM alike to push for new electric and hybrid vehicles seems to me is to show case their technological capabilities and ride along the buzz generated many years ago when the first generation Prius first hit the road. Using the technologies available to us today and in the immediate future, the advantage in terms of environmental impacts of these alternative vehicles such as the hybrid and electric cars remains unclear. And at their current state, it is doubtful that these alternative drivetrains make any economical sense.

Take electric cars for example. From an environmental point of view, while electrical vehicles by themselves do not generate any greenhouse emissions like their gasoline and diesel counterparts, the manufacturing process of the batteries that go into these EVs are likely to have a high environmental impact. The extraction of precious metals and the creation of some of the chemical compounds that used in these high energy density battery packs are likely to consume more energy than the well established process for engine manufacturing. And much of that energy is coming from electrical power plants that use fossil fuel for electricity generation. The “cleaner” nature of EVs is merely because of the redistribution of pollution over different stages of their life cycles and over different geographic areas.

From an economical stand point, today’s manufacturing processes to produce batteries used in the electrical vehicles remain very expensive and the cost of which constitutes a significant portion of the overall cost of the vehicle. And because batteries must be plugged into the grid for charging, it relies on the cost of electricity in order to make economical sense. It seems funny to me that at a time when people prefer natural gas based heating system and shy away from electrical baseboards due to cost considerations, it would somehow be cheaper to charge the EVs off the grid on a daily basis. We know that the power requirement for the electrical vehicles dwarfs some of the most power hungry household electrical systems. Until we are further removed from fossil fuels in our electricity generation process, the cost saving of using EVs is hardly justified. We are having the illusion of savings due to government subsidy and the lower day-to-day operating expenses. The initial investment buying an EV, however, is likely to be much bigger than that of a traditional gasoline counterpart.

Reliability remains a big concern for EVs and hybrids, particularly for EVs. As I discussed before, given the complexity of the hybrid powertrains and the inherent reliability issues of the battery banks, it remains unknown how the long-term reliability (e.g. over a time span of 20 years) of these EVs compare against that of the more traditional vehicles. So even though electric motors are generally much more reliable than gasoline engines, the current state of battery technology significantly limits the overall reliability of these battery powered vehicles.

Another not-so-obvious problem of EVs is related to the power-hungry auxiliary systems (e.g. Heater, air conditioner, audio amplifier, etc). Using these systems will significantly shorten the advertised range and EVs may have to rely on an alternative power-generating unit (e.g. a regular gas powered motor) to generate the additional power needed while using these auxiliary systems.

To improve EV performance, companies have invested heavily and concentrated on reducing the overall weight of the vehicles by using lighter materials such as carbon fibers for the body frames. If we were to adopt a similar approach in today’s gasoline car manufacturing process and reduce the weight of the vehicles, we would significantly reduce the power requirement and thus be able to reduce the engine sizes and ultimately reduce emissions as well.

So, the long term viability of the current electrical vehicles remains to be seen.

References:

• Chevy volt to get 230 mpg rating
• Slashdot comments on Chevy Volt Rated At 230 mpg In the City
• Electric Vehicles and the Environment
• http://www.typesofenergy.co.uk/electric-vehicles-environment.html
• A Different Take on the GM Volt Announcement
• Chevy Volt (part II): 230 MPG, but at what cost?

Before I begin to explain, I wanted to clarify that the title of this post is “Do Hybrid Cars Really Save Energy” not “Do Hybrid Cars Really Save Money”. Why would I make this differentiation? Well, given the upward trend of gasoline price for the entire life span (assuming more than ten years) of cars, hybrids may indeed save money at the end even though the actual amount might be quite small. But here I would argue that hybrid cars, from production till the useful life spans end, actually use more energy then the gasoline powered vehicles. The reasoning is as follows:

1. Rechargeable lithium-ion batteries take significant amount of resources to make (which translate to the energy needed to build such batteries). While I do not have the numbers, it is conceivable that a lot of energy is required to extract Lithium and form the chemical compound that is used in side the battery.

2. The energy density of batteries is inherently much less compared to gasoline. For lithium-ion batteries, the energy density is 0.54–0.72 MJ/kg. While for gasoline, the energy density is 46.9 MJ/kg. So from a MJ/kg perspective, gasoline is roughly 80 times more efficient than lithium-ion batteries. Even though a gasoline engine’s efficiency is typically around 30% and a electric motor’s efficiency can easily achieve 90%, factoring this difference, gasoline is still 20 times more efficient than lithium-ion batteries as far as power is concerned. Thus, when the vehicle moves, the power required to offset ground resistance is more for hybrids then for conventional vehicles given the same output powers of both powertrains.

3. Hybrid powertrain also cannot be as reliable as gasoline only powertrain given the fact that it has many more moving parts (see my post simple is beautiful) . This is by pure law of physics. So hybrid cars need more maintenance then its gasoline only counterparts and maintenance itself requires energy.

4. Worse yet, the failure modes of gasoline engines have been well understand for more than a century and the engine manufacturing processes have matured to a point that engines manufactured these days generally last for twenty or more years. And the output power of a given engine does not significantly degrade as the engine ages. Batteries, on the other hand, ages much faster. Given the way how hybrids’ batteries are constructed (hundreds of serially connected cells), any single cell’s malfunction translates into the failure of the whole battery. So the life span of battery packs is significantly less than engines. Even if all the cells remain functional the cell capacity degrades significantly over the time. So at the end of the life span, a battery pack might only have 60% of the capacity than when new and yet carries the same weight. All these translate into less efficiency over time and thus consume more and more energy to maintain the same performance.

The above points explain why at current stage, hybrid vehicles use more energy during their useful years than their gasoline counter parts. So if you really care about the environment, you might want to think twice before choosing your next vehicle. A conventional vehicle with a reasonably sized engine might be a wiser choice.