22 Jul 2014

In part two of this three part series, we’ll take a closer look at the electric vehicle advantage and energy efficiency advantage

Electric vehicles (EVs) have advantages over fuel cell vehicles (FCVs) in some areas, making EVs the better choice for certain applications. The efficiency of an EV is unsurpassed, and it will always take more energy to get from point A to point B in an FCV. The most efficient production EV currently available is the 2014 Chevrolet Spark EV, which achieves an EPA rating of 260 Wh/mile City/310 Wh/mile Highway/280 Wh/mile Combined (equivalent to 128 MPGe City/109 MPGe Highway/119 MPGe Combined). The higher efficiency is due, in part, to the ability to capture regenerative braking energy, but also because the electrochemical reaction in batteries is more efficient than the reaction in a PEMFC. For FCVs to recapture regenerative braking energy, the PEMFC system would have to also work as an electrolyzer to split water into H2 and O2. This would require a source of water on board the vehicle that could be pumped through the fuel cell. This water source would take up space and could become depleted over long trips, and would also need to be replenished. Obtaining water exiting the cathode of the fuel cell would add to system complexity, and obtaining it from an off-board source requires extra plumbing. A method for eliminating the produced O2 would also be required. More problematic would be how to store the produced H2, which would be at a much lower pressure than the H2 stored in the tank, and thus would have to be pressurized - this would require some time in which hydrogen exiting the tank for propulsion would not be possible. Regenerative braking performed by the fuel cell would therefore be less efficient and make the vehicle less responsive than regenerative braking by batteries.

The EV is also simpler technology that does not cost as much to build. In fact, for a commuter or city car, and especially for a driver that never needs to drive very far and can charge their EV in the garage at night, an EV is very tough to beat. The efficiency spectrum ranges from conventional internal combustion engine (ICE) vehicles to EVs, with FCVs somewhere in the middle.

EVs also are more responsive than FCVs: It is faster to get current from a battery than it is to (1) draw hydrogen from the tank and (2) supply air to the fuel cell to (3) produce the equivalent electricity in a PEMFC to power the electric motor that propels the vehicle.

But what are the competing or complementary technologies of EVs and FCVs? We’ll take a closer look next week during the follow-up blog post. If you have any questions related to this topic today, please leave them below and one of our experts will get back to you.

You may be interested in...