A growing majority of hybrid propulsion systems are series hybrids, in which the engine only charges the battery; it never drives the wheels. As explained in the IDTechEx report, "Range Extenders for Electric Vehicles Land, Water & Air 2015-2025," conventional piston engines used as range extenders are now being questioned because they are not a good starting point in terms of low cost, weight, and size, while also being highly reliable and extending vehicle lifespan.
The development of these "reciprocating engines," as opponents call them, is being challenged because many simpler alternatives are beginning to be considered viable. That said, support for such piston engines is advancing, as seen in the Polaris single-cylinder range extender and inline free-piston engines that directly provide electricity. This seems to be more due to a reluctance to invest than a technical problem.
An example of the potential for piston leakage stems from the fact that jet aircraft have auxiliary power units (APUs) used as a constant load in the tails of jets for non-flight ground installations. Derivatives of such Capstone turbines have had modest success as range extenders for buses and trucks, with the total cost of ownership being one of the limitations.
Bladon Jets in the UK is developing small, handheld jet engines. Cost reduction is achieved through miniaturization, with only one moving part, and they are sold in volume as household and office electrical appliances in countries like India. The blades and shaft are welded as a single piece.
In an alternative approach, Monash University in Australia, in collaboration with Safran Microturbo of France, has made a small jet engine using 3D printing. Adding to this, it wastes very little material, potentially resulting in even lower range extender costs than gas turbines. In fact, Rolls Royce in the UK is already manufacturing jet engine components this way, which will be ready for flight later this year. Both companies are achieving more complex shapes and demonstrating how to reduce costs. Monash uses 3DP lasers, while Rolls Royce uses 3DP electron beams.
Microturbo, a member of the Safran Group and a subsidiary of Turbomeca, designs, develops, and manufactures low-power gas turbines. Microturbo has become a global leader in small, robust, and reliable turbines and turbojets. They work on two product lines: APUs for aircraft, helicopters, and ground applications, and turbojet engine and starter systems for missiles and targets.
A Change of Course with Fuel Cells:
Fuel cells are just another "new" range extender if we ignore the fact that they've been around for about 175 years and focus on the fact that they're still going to be successful in vehicles. Enthusiasts keep talking about the next five years, when the problems of cost, maintenance, size, charging infrastructure, and so on will begin to be overcome to the point of production at the anticipated volume. For example, Toyota expects to produce tens of thousands of fuel cell cars.
Fuel cell materials developer ACAL Energy notes that "a number of cutting-edge technologies to be incorporated into the second generation of fuel cell vehicles between 2020 and 2025 overcome all these issues, and ACAL Energy's liquid catalysts will be part of this. ACAL's liquid catalyst technology addresses the problems of:
• Instantaneous response to charging
• Elimination of all cathode degradation mechanisms
• Robustness – ability to operate with membrane pitting
• Simplified plant balancing
• And a 50% reduction in catalyst price compared to the required Pt cost target.
Battery/supercapacitor technology is complementary to FC powertrains, as all automotive OEMs are committed to some form of hybrid drive system."
Proton Motor has been developing fuel cell vehicles for 20 years with its own fuel cell stack design and system design expertise. They are currently developing a range-extending fuel cell bus system with a 25 kW fuel cell output and an integrated battery capacity of between 80 and 120 kWh, depending on the driving cycle. This concept will allow a 12m³/18-tonne city bus to operate in two shifts with a hydrogen refueling time of 10 minutes. The cost for the bus is in line with the EU's 2020 target, they told IDTechEx.
The advantages include fast refueling, full operating range, lower weight and higher payload compared to a pure battery bus, fewer batteries on board (reducing resource consumption and the challenges of recycling large quantities of batteries), low maintenance compared to a bus with a large fuel cell system, a long fuel cell lifespan based on optimized operating mode, and a longer battery lifespan, as it can be operated within an optimized state of charge (SOC). Will it cost to be competitive? The BYD B9 is the size of a bus, and several thousand have already been sold, but its charging time is 30 minutes or more.
Certainly, more fuel cell cars are appearing, albeit in small numbers. While fuel cell bus trials peaked ten years ago, the architecture is hybrid, with the fuel cell acting as a range extender. There's a large NiMH or Li-ion battery, or a supercapacitor, combined with a conventional battery, handling startup, energy harvesting, and load variation management. See also the IDTechEx report "Electric Buses 2015-2025."
Given the slow pace of improvements and increasing competition from the development of greener, pure electric vehicles, attitudes have shifted this year, with developers realizing they must be open to and accept help from all sides. At the recent World Smart Energy Week in Tokyo, GM, which formed an alliance with Honda to develop fuel cells out of a need to reduce risks and necessary investments, is now calling on suppliers to get closer to them.
Toyota recently made its fuel cell patents open for a limited time to try to accelerate progress—its Mirai fuel cell car is sold in very limited quantities, presumably due to costs. In Japan, Toyota told IDTechEx that they can guarantee 200,000 kilometers of fuel cell durability—a big improvement with an old problem—but they don't know how the resale car market will evolve. Very low resale prices for battery electric cars have inhibited sales, and the same will likely happen for fuel cell cars for some time.
Volkswagen said its position on fuel cells is that they are not fully convinced that fuel cell cars will be widely deployed. They will not invest heavily and will use a gasoline car platform for their fuel cell car development. They are concerned about how zero-carbon fuel cells in cars will ultimately be supplied with hydrogen from fossil fuels and the complexity of manufacturing them. In fact, a hydrogen fuel cell typically emits one kilowatt of heat for every kilowatt of electricity used.
By Dr. Peter Harrop, President, IDTechEx
