Sustainability is no longer a nice to have. It is a global imperative. In 2018, flights worldwide produced 895 million tonnes of CO2. The global aviation industry produces around 2% of all human-generated CO2 emissions.
The ICAO have published an objective to reduce aviation’s net carbon emissions by 2050 to 50% of what they were in 2005. As other areas of society improve, aviation must improve as well.
At Hybrid Air Vehicles (HAV), sustainable air services are at the core of what we do. With news flashes every day of the latest green technology, we take a look at the technology that could shape the future of air travel.
Hydrogen Fuel Cells
Hydrogen has the highest specific energy of any available fuel source, containing significantly more energy by mass than jet kerosene. There are a number of companies working on a way to make it a viable solution for aviation despite its low energy density meaning it requires a lot of storage space.
Hydrogen fuel cells create electricity by combining hydrogen stored in a tank with ambient oxygen via a proton exchange membrane, emitting only water vapour as a by-product, meaning they are zero carbon at the point of use.
The carbon footprint of hydrogen fuel cells does come into question. Firstly, there is the energy expended in the manufacturing process (from the extraction of raw materials, to the electricity consumed in manufacture, to the delivery of the cells to the end user). Secondly, the through-life creation of hydrogen to refuel the fuel cells, this is only as green as the electricity that feeds the electrolysis process to split water into hydrogen. Finally, there is the environmental cost of fuel cell disposal at the end of life.
Hydrogen fuel cells are certainly a technology HAV are keen to follow as we look for the most efficient ways to power our aircraft.
Current battery technology works only for smaller aircraft travelling shorter distances. Once we go beyond these shorter flights, batteries are no match for any fossil fuel as they weigh considerably more for the same energy.
With continued investment of time and money into automotive electric vehicles, battery technology is improving, but the journey is slow. The MRO Network reports that power density of batteries will improve by a factor of three in the next 10 years.
Similarly to hydrogen fuel cells, battery technology can contribute its own carbon footprint. Again there is the energy expended in the manufacturing process, including the acquisition of materials. There is also the through-life recharging of the batteries to consider and this is only as green as the electricity that feeds it (for example solar or wind energy versus coal or oil generated energy).
There is also the concern of battery disposal. Some battery technologies such as lithium-ion are not suitable for landfill due to possible reactions with water, meaning finding ways to recycle them will be imperative. As of yet, the infrastructure for recycling batteries in large volumes has not been developed, but a number of organisations are working on it.
Biofuel introduces less CO2 into the atmosphere compared with refined crude oil.
Biofuel has been used for a number of years now, with the first flight taking place in 2008. Currently biofuel is relatively rare, only a number of airports have regular biofuel distribution and due to the production costs its use could result in ticket cost premiums.
Biofuel may be a solution that is available now, but the growth of feedstock is problematic, with the need for fertilisers, herbicides and pesticides, which are all detrimental to the environment. There are companies out there, like SAF+ Consortium, who are working on options that avoid this problem. SAF+ capture and convert flue gas obtained from industrial sources eliminating the need for biomass feedstocks.
Airlander’s current diesel engines could be converted relatively easily to run on biofuels and this is one of the early potential paths towards improving the already low environmental impact of Airlander.
In 2016, the Solar Impulse 2 circumnavigated the globe covered in 17,000 photovoltaic cells, charging the batteries which powered its motors.
However, with the weight of solar cells and batteries and the amount of power they can produce, we would need to see significant advances in efficiency before they are a feasible option for powering a commercially viable aircraft.
Maybe an aircraft like Airlander would have the surface area needed to make them an option for the future.
There is much movement in the world of electric propulsion – it is an area we are looking into ourselves, alongside Collins Aerospace and the University of Nottingham with our E-HAV1 project (grant supported by the UK ATI).
There are many other big industry players becoming involved in the development of electric motors for aviation use as well. One example is Airbus and Rolls Royce’s E-FAN X project, where they plan to replace one out of four jet engines on a conventional commuter airplane with a 2MW electric motor for testing.
Where does Airlander come into this?
Airlander is inherently efficient in its design. The design of Airlander combines buoyant lift from helium with aerodynamic lift and vectored thrust. This creates a significant efficiency over conventional fixed and rotary wing aircraft. In fact, Airlander uses between 1/4 and 1/3 as much as fuel as other aircraft performing the same task.
HAV is already in a good position compared to airplanes and helicopters at the start of the journey towards a green aviation future, but we’re not resting on our laurels. We have teamed with Collins Aerospace and the University of Nottingham to develop high efficiency 500kW electric propulsors (the EHAV-1 project) to replace two of Airlander’s four engines to create a hybrid fuelled version of Airlander. This variant of Airlander will be capable of two to four hour zero emission flights on electric power alone whilst retaining the multi-day capability through the use of its remaining two diesel engines. As electric power storage and propulsion systems continue to evolve and mature Airlander will make the step to an all-electric configuration as customer demand increases.
To find out more about our E-HAV1 project you can read the full news article here.