Hybrids

Transportation is the second largest cause of CO2 emissions in the US. As our population continues to grow, this will only increase. Furthermore, as developing nations like China, India and others become more and more industrialized, the need for transportation will exponentially grow throughout the globe. This obviously creates a need for vehicles that are more efficient and emit fewer (or zero) GHGs. Also, developing vehicles less dependent on oil will help to diversify our energy portfolio, lessening our reliance on foreign resources.

My current senior design project at Northeastern is related to the automobile industry, forcing me to conduct a great deal of research and learn quite a bit about hybrid vehicle technology. Surprisingly, there are quite a few options out there for vehicles that aren't completely driven by an internal combustion engine (ICE).

Some of the major alternatives to these ICE vehicles are categorized as the following: electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and hybrid hydraulic vehicles (HHVs), and more recently fuel cell vehicles (FCVs).

One of the best resources I have found for analysis of alternative vehicle technology is The State of the Art of Electric, Hybrid and Fuel Cell Vehicles, written by C.C. Chan, a fellow of the International Association of Electrical and Electronics Engineers (IEEE).


Electric Vehicles
At the start of the industrial revolution, many thought the electric vehicle(EV) would become the primary mode of transportation. In fact, the first car ever made by Ferdinand Porsche was an EV, built in 1898. However, limitations with battery technology at the time and developments in the mining of fossil fuels allowed combustion engines to reign supreme for the next century. In the future, electric vehicles provide the most opportunity for emissions free personal transportation. However, I don't think they are the best solution for the time being.

EVs use battery technology to store energy in the form electicity and then utilize this to power an electric motor for propulsion. The car itself uses zero oil, gasoline or fossil fuels. But, the reason why I don't think EVs are the best solution today is because the majority of our electricity is generated from coal run power plants or from other fossil fuels. We do need to develop our battery technology, but this should not be our primary focus. We must first fund the development of other clean energy technologies like wind, solar, nuclear, gasification and developing a more capable electric grid. Once this is done and the majority of our electricity is derived from clean resources, EVs will then be the appropriate solution. If we develop these EVs first without adapting the source of our electricity, it will appear like we are reducing our dependence on fossil fuels, when in fact we're not.

EVs on the market today use lithium-ion batteries and have a range on the order of 100 to 150 miles per charge. However, eventually these batteries will need to be replaced, a cause for concern due their cost, as well as the fact that lithium is an alkali metal that is also a limited resource. While EVs have a very promising future, we shouldn't be throwing all of our eggs in this basket until we can adequately support this technology.


Hybrid Electric Vehicles
The majority of hybrids you seen on the road today are likely hybrid electric vehicles (HEVs). The Toyota Prius and Honda Civic Hybrid, for instance, are HEVs. I'd be willing to bet that a large portion of automobile users don't even really know what "hybrid" infers, however.

In laymen's terms, an HEV combines an electric motor with an ICE to generate power. The technology is actually fairly sophisticated and pretty incredible. HEVs can be arranged in various configurations, primarily "in series" or "in parallel".

Series means that the mechanical output of the ICE is first converted to electricity through a generator and then fed through the electric motor to accelerate the car. This actually makes it an ICE assisted EV, as the electric motor becomes the primary propulsion unit. However, the efficiency of this system is usually lower due to the use of two systems in series. This system allows the car to run on the electric motor alone (powered by batteries), the ICE alone, or both in series.

A parallel HEV is somewhat different. Here, the electric motor and ICE are separated, and then indivicually linked to the driveshaft using two clutches. This makes it an electrically assisted ICE vehicle as opposed to the series setup. The electric motor can charge the battery through regenerative braking or by absorbing power from the ICE when it generates more than the required load. This is a more simple setup than a series vehicle, as a generator is not required. The majority of hybrids on the road today are parallel HEVs. The electric motors for these vehicles range from 2.5kW at 12V ("micro" hybrids) to 50kW at 200-300V (full hybrids, i.e. the Prius). The Honda Insight is somewhere in between and classified as a "mild hybrid" (10-20kW motor at 100-200V). Most hybrids on the road can be fueled at gas station, but there are some that can be plugged into the electric grid to power the batters (plug-in HEV, PHEVs). A PHEV has a range of about 18-36 miles when only running on the electric motor. This virtually makes it a limited range EV, and is the most efficient when you only need to drive short distances.

Difficulties with all HEVs are assosiated with the cost as well as limitations in the batteries. However, recent improvements have been made in each of these areas. In fact, the 3rd generation Toyota Prius starts at only $22,000 and boasts 51/48 mpg (city/hwy).

Fuel Cell Vehicles (to be continued...)