Electric Vehicle Range Extension Using a High Temperature PEM Fuel Cell

Vehicle electrification is all the rage. In March 2009, President Obama pledged to have 1 million plug-in hybrid electric vehicles on US roads by 2015. Through the Recovery Act and other grants, billions of dollars are being spent to support the introduction of electric vehicles (EVs) into mainstream markets. The goals are to reduce America's dependence on foreign oil, reduce pollution, and reduce the US carbon footprint.

EnerFuel, a wholly owned subsidiary of Ener1 (NASDAQ: HEV), has been developing electric vehicle range extenders using its proprietary high temperature PEM (HT-PEM) fuel cell system. The range extender assists the vehicle battery power for additional propulsion and acts as an onboard battery charger while the vehicle is parked or idling. The result is increased electric vehicle range without toxic pollutant emissions.

Electric Vehicle Adoption

Widespread market adoption of EVs is anything but assured. The migration of vehicle powering technology from the traditional internal combustion engine (ICE) to the battery requires accepting a difference in vehicle performance along with a change in consumer behavior.

In May 2010, Deloitte Consulting LLP published a study, Gaining Traction: A customer view of electric vehicle mass adoption in the U.S. automotive market, reporting that in a survey of potential EV customers the most important barriers to the purchase of an EV are price, range and vehicle size. The same study states that while an EV with a 50 mile range would meet the daily needs of most drivers, 70% of drivers expect an EV to travel 300 miles. Most EVs are being designed with a driving range of 100 miles or less.

The Deloitte study also assessed potential consumer attitudes towards EV charging. Most consumers want to charge their EVs at home; however 61% of those surveyed do not have access to a garage with an electric power source. The report finds that charging time (i.e. the amount of time the vehicle must be plugged-in to go from its minimum to maximum state of charge) is a major contributor to vehicle adoption. Only 17% of those surveyed were willing to charge at home for a period of 8 hours. A reduction in this requirement from 8 to 4 hours doubled consumer willingness to purchase the EV.

The differences between EVs and ICE vehicles (e.g. no vehicle emissions, no engine noise) are an important selling point. However, these differences must not assume users are willing to accept abrupt lifestyle changes.

The Fuel Cell Range Extender Solution

A high energy density power generator is one way to eliminate the EV range issue. The typical plug-in hybrid electric vehicle (PHEV) and extended range electric vehicle (EREV) uses an ICE as the generator. Yet, the ICE has many detriments with respect to fuel cells. Most importantly, ICEs produce toxic emissions (NOx, SOx, CO, particulate matter, etc.), operate at relatively low efficiencies, and require an alternator to convert mechanical power to electrical power at the voltage required by the vehicle battery. They also introduce noise and vibration to the vehicle.

The fuel cell is another technology that can serve as a high energy density power generator, however, fuel cells also have limitations. They are expensive and they require hydrogen. EnerFuel is developing a solution that eliminates these barriers. The company's approach consists of using a relatively low power fuel cell (3kW to 5kW) in conjunction with a reformer to create a low cost fuel cell system that can be fueled with conventional fuels (e.g. gasoline, diesel, biodiesel, ethanol, natural gas, or others).

There have been many failed attempts at commercializing vehicle fuel cell systems with an integrated on board reformer. EnerFuel's solution has significant distinctions over these attempts. For one, the fuel cell operates between 120°C to 180°C allowing much greater tolerance to contaminants in reformer-produced hydrogen. Also, the fuel cell system operates at discrete power conditions with minimal transients and the system is smaller (and less complex) than previously attempted onboard reformation systems.

These key attributes dramatically simplify overall system design, reducing cost and increasing energy density. Fuel cell operation at high temperatures reduces the need for pure hydrogen from the reformer; a primary technical barrier for the use of reformers with low temperature (60°C to 80°C) PEM fuel cells. The hybridization with batteries reduces the requirement for immediate fuel cell start-up, which allows EnerFuel to use HT-PEM fuel cells.

EnerFuel designed its HT-PEM fuel cell systems with minimal balance of plant. For example, reactant humidification is eliminated, an air cooled design eliminates the need for a coolant loop and radiator, and low pressure operation reduces the need for compressor-expander systems. Balance of plant elimination helps to reduce the cost and increase the reliability of the fuel cell. While the fuel cell stack cost drops almost linearly as its nominal power output drops, the balance of plant of plant costs do not scale down in the same manner. Thus, the EnerFuel HT-PEM fuel cell system can have a cost advantage over more complex systems in this application.

The Customer Experience

Perhaps the most important difference between a fuel cell and an ICE range extender is that the fuel cell can charge the battery while the vehicle is parked. This is possible because the fuel cell does not produce toxic emissions, so its operation is not detrimental to the immediate environment. Moreover, fuel cell efficiency increases at partial loads, whereas ICE efficiency decreases at partial loads. Depending on the rate of charging required, the efficiency of fuel cells is many times higher than that of ICE and on occasion is higher than the grid efficiency. This translates to higher gas mileage, lower well-to-wheel carbon emissions, and lower toxic emissions, all which enhance the green credentials of the vehicle.

The EV market would be able to grow without a dependence on a charging infrastructure. Imagine your level of satisfaction when upon commuting to work and parking your EV at a battery state of charge of 60% in the morning, you find it at full state of charge when getting ready to fetch some lunch. In essence the fuel cell is a high efficiency, zero pollution portable-charger for your vehicle.

More complex battery-fuel cell interactions can also occur. For example, the heat generated by the fuel cell can be used to keep lithium ion batteries warm in cold environments, increasing the life of the batteries. The fuel cell can also help support battery and vehicle air conditioning loads.

To keep the cost, size, and weight of the fuel cell down, EnerFuel is developing lower power fuel cell systems than those traditionally placed in vehicles. Typical previous fuel cell vehicles use a fuel cell system that provides 60kW to 100kW. EnerFuel is developing 3kW and 5kW systems.

At these power levels, the fuel cell would be unable to meet the average power (rate of electrical energy) demand from vehicles under normal driving conditions. Although the fuel cell is running while the vehicle is operating, the battery state of charge would still decrease (albeit slower) under most conditions.

However, 3-5kW would produce enough energy throughout the day to meet the average daily power consumption. The increase in range provided by the fuel cell would be a result of battery recharging when the vehicle is parked and defrayment of battery energy when the vehicle is driven.

As an example, take a vehicle with a 200Wh/mi average driving energy consumption (equivalent to a 25 to 33 mile per gallon gasoline ICE vehicle). To travel 100 miles throughout the day, the vehicle would require 20kWh batteries. If a 5kW fuel cell system were added and allowed to charge the vehicle batteries without limit throughout an 8 hour day, it would be able to add 40kWh of energy to the vehicle. The daily range of the vehicle would be 200 miles from the fuel cell and 100 miles from the battery, a total of 300 miles. In this scenario, the vehicle efficiency would range between 75 to 100 miles per gallon depending on how the fuel cell is operated.

Few people engage in such a long daily driving cycle, which opens up the possibility of eliminating a portion of the batteries. In this way, the overall cost and weight of the vehicle power plant can be significantly reduced.

The Demonstration

In 2008 EnerFuel developed a test platform vehicle that demonstrated the advantages that the fuel cell EV range extender could provide. EnerFuel used an EV with a 20kWh lithium ion battery pack. The vehicle was outfitted with a 3kW fuel cell range extender. The fuel was compressed hydrogen. The range extender increased average vehicle range by more than 50% from the battery only base case. The overall weight of the fuel cell system was 160lbs. The weight of a lithium ion battery pack with similar energy content would have been double that of the fuel cell. EnerFuel is currently integrating its next generation, reformer-based fuel cell into an EV to demonstrate its onboard reforming application.

A Final Word

The addition of a fuel cell range extender to an EV offers tremendous benefits. This technology represents a new way to implement an old way of thinking. In the end, customers will decide if electric vehicles are a niche toy for the environmentally-friendly drivers or a worthwhile product suitable for the masses. EnerFuel believes that the option of a fuel cell range extender will encourage adoption for the latter.