The Concept of emission free flying


The reason

In 2014, the transport performance in Germany amounted to 1,167 billion km1, while aviation accounted for 58 billion km, or 4.9%.
Thus, compared to other means of transport, aviation has the lowest transport performance, but with an average of 211g2 CO23 per passenger kilometer it produces the largest share of pollutant emissions in transport.

(c) H2Fly

This adds up to 12.2 million tonnes of CO22 generated solely by aviation in Germany in 2014.
Furthermore, the following figure clearly shows that the increase in CO23 produced by aviation between 1995 and 2014 was the largest of all means of transport (78%), with a further upward trend.

(c) H2Fly

In the European Union, this development has been reacted to, so that by 2020, the pollutant levels must be reduced by up to 40%. In addition, airlines are to participate in emissions trading with CO2 certificates, which brings an economic motivation for the reduction of pollutant emissions. Here, the introduction of emission-based landing fees reflects the political desire and the need to minimize pollutant and noise emissions at airports.

The concept

In order to massively reduce the emissions produced by aviation, alternative electric drives can be used for medium distances as well as for operation on the ground. In principle, emission-free electric drives can be adapted from terrestrial use for using in an aircraft. Regenerative energy is stored, which in turn is converted into kinetic energy in an electric motor and provides for the propulsion of the aircraft. However, the central question remains, how the energy for the driving electric motor should be provided.

The problem

The hype surrounding battery-powered aircraft has skyrocketed in the past and is further compounded by politics and the media. However, a pure battery storage has some drawbacks for aviation applications. The limited range as well as the depletion of rare earth ressources into emerging economies to produce the many necessary battery cells (150-200 kg CO2 / kWh4) are disadvantages that are incompatible with today’s standards of mobility and environmental objectives. For example:  If you want to equip a conventional 19 seater (977kg for storage and propulsion = 2t for passengers or cargo) with a pure battery drive, so even at 400 Wh / kg (Gravimetric Energy Density of the Bat. System) the maximum  allowable takeoff weight is exceeded by approximately 1, 2 tons and would have transported 0 passengers. However, one advantage, is the high power density of the battery for high power demand (during take-off and go around). With a hydrogen (high energy density) hybrid drive, the number of batteries could be significantly reduced and a payload of 615 kg for passengers realized. A completely emission-free drive without compromise is thus possible.

The solution

One way to increase range and functionality is the use of hydrogen fuel cells for a full electrical hybrid. Unlike batteries, power and capacity can be decoupled in fuel cells, allowing a significant increase in range with a small increase in weight. Also, the low refueling time on the ground is another advantage of this key technology, which means that turnover times meet today’s standards. The battery buffer for the high performance requirements can be dimensioned much smaller, which saves weight and resources. The recharging times are simply transferred to the air as the fuel cell can feed excess energy back into the battery during operation. You will get a full electric and emission free drive with no restrictions on mobility.

The operating principle

For the use of hydrogen, an additional conversion step is necessary, the first in the fascinating circle of hydrogen utilization. By electrolysis of water,  the splitting of water, regenerative electrical energy can be converted into the chemical energy source hydrogen and the vital element oxygen. The hydrogen produced in this way is stored in pressure tanks and made available to the Hy4 as regenerative fuel. Basically, in a fuel cell now the electrolysis is reversed. It converts hydrogen back into water and electric current using oxygen from the air, which drives the electric motor and the circuit closes.

1: Statistisches Bunddesamt, Fachserie 8 Reihe 1.2,2014
2: Umweltbundesamt, Bezugsjahr 2014
3: CO2 Äquivalent, beinhaltet CO2, CH4 und N2O
4: Study C243, The Life Cycle Energy Consumption and Greenhouse Gas Emissions from Lithium-Ion Batteries