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Author: Daniel A. Betts
Vehicle electrification is all the rage. On 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 into mainstream markets. The goals are to reduce dependence on 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 can act as an onboard battery charger that can be used when the vehicle is parked or idling, or used together with the vehicle batteries to provide the electrical power necessary for vehicle propulsion. The result is increased electric vehicle range without toxic pollutant emission.
Electric Vehicle Adoption
Widespread market adoption of EVs is anything but assured. The change of energy technology in the vehicle also portends a difference in vehicle performance from the traditional internal combustion engine (ICE) vehicles with a commensurate change in consumer behavior.
A study published by Deloitte titled Gaining Traction, reports 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 66% of drivers on weekdays and 70% of drivers on weekends, 70% of drivers would expect an EV to travel 300 miles. Most EVs are being designed with driving ranges of 100 miles.
The Deloitte study also assessed potential consumer attitudes towards EV charging. Most consumers would want to charge their EVs at home, however 61% of those surveyed did not have access to a garage with an electric power source. Moreover, the report suggests that charging time (amount of time the vechicle needs to remain plugged-in to get a full 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 charge the vehicle.
EV differences with the ICE vehicles are an important selling point (why change it to keep it the same?). However, these differences must not be difficult to embrace and must be flexible in order to accommodate a wide range of lifestyles.
The Fuel Cell Range Extender Solution
To eliminate the EV range issue a high energy density power generator is required. The typical plug-in hybrid electric vehicle (PHEV) and extended range EV (EREV) uses an ICE as the generator. Yet, the ICE has many detriments with respect to fuel cells. Most importantly, they produce toxic emissions (NOx, SOx, CO, particulate matter, etc.), they 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.
Yet fuel cells have limitations of their own. They are expensive and they typically require hydrogen. EnerFuel has been working on eliminating these two 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.
While the incorporation of a reformer with a fuel cell has been tried in the past, the present differs from prior efforts. One, the fuel cell operates between 120oC to 180oC; two, the fuel cell system operates at discrete power conditions with minimal transients; and three, the system is smaller than previously attempted onboard reformation systems.
These key attributes dramatically simplify overall system design, reducing cost and increasing energy density. For example, 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 (60oC to 80oC) PEM fuel cells. The deep hybridization with batteries also reduces the requirement for immediate fuel cell start-up, which allows EnerFuel to use HT-PEM fuel cells.
EnerFuel has designed HT-PEM fuel cell systems with minimal balance of plant. For example, reactant humidification has been 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 is critical to the cost and reliability of the fuel cell. While the cost of the fuel cell stack 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
To the user perhaps the most important difference between a fuel cell and an ICE range extender is that the fuel cell can charge the vehicle battery while 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 system efficiency increases at partial loads, whereas ICE efficiency decreases at partial loads. Therefore, depending on the state of charge of the vehicle battery or the rate of charging that is required by the user, the efficiency of charging can be many times higher than that of ICE and on occasions 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 user would find a reduced 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 90% state of charge when getting ready to fetch some lunch. In essence the fuel cell can act as a high efficiency, zero pollution portable-charger for the vehicle.
More complex battery-fuel cell interactions can also occur. For example, the heat generated by the fuel cell while running or during its startup phase can be used to warm up lithium ion batteries in cold environments. The fuel cell can also help support battery and vehicle air conditioning loads.
To keep the cost, size and weight of the fuel cell low, EnerFuel is developing lower power fuel cell systems than those traditionally place in vehicles. The typical fuel cell vehicle uses a fuel cell system that provides 60kW to 100kW. EnerFuel is developing 3kW and 5kW systems.
At this power levels, the fuel cell would be unable to meet the average power (rate of electrical energy) demand from common vehicles under average driving conditions. Although the fuel cell is on while driving, the battery state of charge would still drop under most conditions.
However, the fuel cell would be able to meet the average power demand of daily vehicle driving. 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.
Seldom people engage in such a long daily driving cycles, which opens up the possibility of eliminating a portion of the vehicle batteries. In this way, the overall cost and weight of the vehicle power plant can be reduced.
Conclusion
In 2008 EnerFuel developed a test platform vehicle that demonstrated the advantages that the fuel cell EV range extender could provide. EnerFuel used a 2008 electric vehicle 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.
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