The rationale for the focus of this article is that hydrogen storage and fuel cell electric vehicles come into their own compared to battery electric vehicles, when a driving range between recharging comparable to today’s diesel or petrol vehicles is required.
A recent review conducted by RMIT School of Aerospace, Mechanical and Manufacturing Engineering (SAMME) researchers found that the best-performing hydrogen storage options (compressed gas at up to 350 or 700 bar pressure, chemical hydrides, or metal hydrides) have a system gravimetric energy density between 2.5 and 3 times that of the best available lithium-ion battery packs.
The system volumetric energy density (energy per unit volume) for the best hydrogen options is approximately 2.5 times greater than that for batteries. These energy density advantages mean that a hydrogen fuel cell vehicle can have a range several times that of a battery electric vehicle, for the same mass and volume of the energy storage and supply system.
Hydrogen fuel cells for trucksArticle continues below…
While there is a major research and development effort internationally on developing hydrogen fuel cell passenger cars, relatively little work is being done on large fuel cell trucks. RMIT sees this as a niche area where it can make a real contribution. Line-haul road trucks also operate on fixed routes between major cities, so just a few hydrogen refueling stations would be needed in the first instance, thus reducing the infrastructure costs of moving to an alternative fuel.
A hydrogen fuel cell truck with its electric power train would have zero greenhouse and other air pollutant emissions, and be very quiet. In this way, many of the adverse environmental and social impacts of operating heavy trucks in urban areas would be greatly ameliorated. The transport sector is currently responsible for nearly 16 per cent of total Australian greenhouse gas emissions with a fifth of this coming from trucks, according to the Federal Department of Climate Change and Energy Efficiency.
A shift to hydrogen produced from renewable resources would also reduce dependence on imported petroleum fuel in a situation where major price increases and instability, as well as potential shortages in supply, may well eventuate over the next ten to 15 years.
A model truck
A scale model of a Scania R470 Highline truck has been converted to hydrogen power at RMIT University to gain practical insight into some of the technical challenges of using hydrogen fuel cell systems for full-scale long-haul trucks. To supply the truck’s direct-current electric motor, two self-humidified 30 watt fuel cell stacks with 7-12 volt (V) voltage output were chosen.
Hydrogen is stored on-board in the solid state using four cylindrical metal hydride canisters (diameter 25.4 mm, length 105 mm) and holding up to 1.5 grams of hydrogen each.
The experimental system is equipped with sensors to monitor the voltage and current delivered to the direct-current motor and to measure the rate of hydrogen consumption during performance tests. A wireless data acquisition system is used to transfer the real time data collected by the sensors to a nearby monitoring laptop.
An important early finding is that the use of a bank of ultra-capacitors (8.3 Farad, 13.8 V) connected across the fuel cell in parallel with the load can effectively buffer the cell’s output to ensure continuous power during purge periods, and assist in meeting sharp increases in demand needed during acceleration. The hydrogen fuel cell system was found to be more responsive to a changing load than the original batteries.
The gravimetric energy density of the fuel cell system was measured to be about 30 per cent better than the original batteries of the truck. Hence, the 6 grams of hydrogen stored on board the model gave an 18 km driving range in approximately 2.6 hours, whereas the original battery pack was able to run the truck under the same driving conditions for only 1.6 km and 14 minutes.
The next steps in the project are to design a full-scale prototype of a hydrogen fuel cell-powered prime mover for a typical semi-trailer.
Making hydrogen renewable
Hydrogen is a zero-emission fuel only if produced using renewable energy sources. Additional research work at RMIT SAMME has therefore been directed at producing hydrogen using electricity from photovoltaic (PV) solar, aerogenerator systems and electrolysis of water.
A collaborative project with the CSIRO Energy Technology Hydrogen Group measured the performance of a 2.5 kilowatt (kW) proton exchange membrane electrolyser made by CSIRO that was coupled to the 2.4 kW PV array in the Renewable Energy Park at RMIT’s Bundoora East campus in Melbourne.
Using a novel matching procedure developed by SAMME researchers, this electrolyser and the PV array were directly coupled, with no intervening maximum power point tracker, voltage converters or regulators, while still yielding very high energy-transfer efficiency. RMIT SAMME was a member of the CSIRO National Hydrogen Materials Alliance (2006-09) alongside ten other leading Australian university research groups, and the Australian Nuclear Science and Technology Organisation, working on hydrogen energy research in Australia.
There have been major gains in the cost-competitiveness of producing hydrogen from solar and wind power over the past ten years. The 2010 United States Department of Energy Report on its hydrogen program showed that the estimated cost of hydrogen from large-scale wind farms and water electrolysis – in the range $US2.70-3.50 gasoline gallon equivalent – is already competitive with conventional gasoline (price at the time of writing: $US3.50 per gallon).
RMIT SAMME is currently conducting a feasibility study for the Victorian Department of Sustainability and Environment on using a solar PV-hydrogen system for a highly reliable and low-maintenance standalone power supply for remote wireless telecommunications stations used for early warnings on forest fires and communication between emergency services units.
Global renewable hydrogen principles
In early 2012, two SAMME researchers also took on the ‘big question’ of where hydrogen might fit into an overall global and national sustainable energy strategy that is consistent with meeting the greenhouse gas emission reduction targets proposed by the Intergovernmental Panel on Climate Change (that is, an 80 per cent reduction by 2050 compared to 2000), and transitioning away from petroleum fuels from transport by the same time horizon. In two major journal papers on this topic, six principles were proposed to guide the role played by hydrogen in sustainable energy strategies:
- A hierarchy of sustainable hydrogen production, storage and distribution centers relying on local renewable energy sources producing hydrogen as required
- Complementary use of hydrogen and electricity as energy vectors to minimise the extent of new hydrogen pipeline distribution networks
- Production of hydrogen from a range of renewable sources and feed stocks, without dependence on nuclear fission power or carbon capture and storage, but with the application of energy efficiency measures to the economic limit across all sectors of the economy
- Recognition of the complementary roles of hydrogen and battery storage across a range of transport vehicles and transport services
- Use of hydrogen for longer-duration energy storage on centralised grids relying extensively on renewable energy inputs.
This re-envisioned role for hydrogen is not as all-encompassing as the original ‘hydrogen economy’ first proposed in the early 1970s, but it is potentially a very substantial role that can indeed be realised with the appropriate levels of research and development support.
Dr Bahman Shabani focusses on conducting applied research in thermodynamics and heat transfer on various systems, in particular: sustainable energy systems, hydrogen fuel cell technologies for both stationary and mobile applications, hydrogen-based energy storage systems, integrated thermal and power systems, alternative fuels and green engines, and energy efficiency.
Associate Professor John Andrews' book Living Better with Less was one of the first works to propose sustainable development for Australia. He played a pioneering role in assessing the potential and encouraging utilisation of wind energy for electricity generation in Australia. His current research interests are in renewable energy – hydrogen systems for remote area power supply, and solar thermal desalination.
Professor Aleksandar Subic is the Head of the School of Aerospace, Mechanical and Manufacturing Engineering at RMIT University. Professor Subic has approximately 25 years of research experience, during which he has achieved over $7 million of research income and over 220 international peer reviewed publications.