EnerFuel Coupling High-Temperature PEM Fuel Cell With On-board Reformer for Range Extender System for Electric Vehicles
|EnerFuel is developing a HT PEM cell/on-board reformer system that enables the use of conventional fuels in the fuel cell range extender. Source: EnerFuel. Click to enlarge.|
EnerFuel, a subsidiary of Li-ion manufacturer EnerDel’s parent Ener 1, is developing a range extender system for electric vehicles that consists of a high-temperature (HT) PEM fuel cell combined with an on-board reformer. The use of the reformer in conjunction with the high-temperature 3-5 kW fuel cell would enable the use of conventional hydrocarbon fuels to recharge the batteries in the EV.
In 2008, EnerFuel developed a prototype to demonstrate the advantages of a fuel cell EV range extender. (Earlier post.) The test vehicle, equipped with a 35 kWh lithium ion battery pack, was outfitted with a 3 kW fuel cell range extender fueled by compressed hydrogen (5,000 psi tank, 20 kWhe equivalent). The range extender increased average vehicle range by more than 50% from the battery only base case, EnerFuel said.
The overall weight of that fuel cell system was 160 lbs (73 kg). The weight of a lithium-ion battery pack with similar energy content would have been double that of the fuel cell system.
|HT-PEM cells have much lower susceptibility to CO poisoning than LT-PEM cells. Source: EnerFuel. Click to enlarge.|
The use of an on-board reformer eliminates the need for a hydrogen refueling infrastructure, EnerFuel notes. While the incorporation of a reformer with a fuel cell has been tried in the past, EnerFuel’s effort differs in the use of the higher-temperature operating range (120 °C to 180 °C, vs. low-temperature 60 °C to 80°C PEM fuel cells). Furthermore, the fuel cell system operates at discrete power conditions with minimal transients, and the system is smaller than previously attempted onboard reformation systems.
The HT-PEM fuel cell has much lower susceptibility to CO poisoning than LT-PEM cells; this enables simplified and low-cost integration with reformers. 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. The EnerFuel HT-PEM fuel cell system thus can have a cost advantage over more complex systems in this application, the company says.
To the user, suggests Dr. Daniel Betts at EnerFuel, perhaps the most important difference between a fuel cell and an ICE range extender such as that used in the Chevrolet Volt is that the fuel cell can charge the vehicle battery while parked. Further, fuel cell system efficiency increase at partial loads, whereas ICE efficiency decreases at partial loads. 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 could be many times higher than that of ICE and on occasions higher than the grid efficiency, EnerFuel says.
The EV user would find a reduced dependence on a charging infrastructure. 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, Betts says. 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. While the typical fuel cell vehicle uses a fuel cell system that provides 60 kW to 100 kW, EnerFuel is developing 3 kW and 5 kW systems.
As an example, EnerFuel uses a vehicle with a 200 Wh/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 a 20 kWh battery pack. If a 5 kW 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 40 kWh 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.
Because people seldom engage in such a long daily driving cycles, this opens up the possibility of eliminating a portion of the vehicle batteries, EnerFuel suggests. In this way, the overall cost and weight of the vehicle power plant can be reduced.
(A hat-tip to David!)