Is Hydrogen the Fuel of the Future?
In a sense, hydrogen is already a fuel for the Autocopter if it uses synthetic kerosene of the Shell variety (see page on Synthetic Fuels), but on this page we mean through hydrogen stored aboard the aircraft and turned into electrical power by a fuel cell. Hydrogen, however, is not the easiest thing to store and fuel cells are currently too bulky and heavy for the Autocopter, quite apart from the certification problems they might give rise to.
In the UK and much of Europe, hydrogen is being looked at more and more as the fuel for the future across a wide range of applications – home heating as a replacement for natural gas, a way of storing the energy produced by wind and solar farms, fuel for automobiles to be turned into electrical power using a fuel cell, feedstock for a synthetic fuel plant, etc.
No doubt companies such as Airbus and Boeing have already looked at the design of hydrogen fuel cell powered aircraft and may well have flown prototype machines.
However, at the end of the day it probably has to be produced sustainably and that means by either electrolysis, a process incorporating carbon capture or something like a nickel-iron battery that can both store the power and generate hydrogen. There are lots of options.
Weight/Power Comparison of Four (Power Plant + Fuel) Combinations
Per unit of weight, hydrogen contains roughly 5 times as much energy as gasoline, diesel or synthetic kerosene, but when you add the weight of the container required to hold the hydrogen, the conversion efficiency of fuel into power and any compensation to account for the requirement of Category A certification, the numbers come out quite differently. What we then do is calculate for each combination of engine and fuel type a System Weight = (engine weight + fuel weight + fuel storage weight), a Dead Weight = (engine weight+ fuel storage weight) and an associated kg/kWh. The battery one is the exception in that there is no engine weight and practically no fuel weight.
. Efficiency System Weight Dead Weight
Gas turbine / Kerosene 40% 0.48 kg/kWh 0.29 kg/kWh
Batteries 95% 4.66 kg/kWh 4.55 kg/kWh
Hydrogen / Fuel Cell 50% 2.16 kg/kWh 2.11 kg/kWh
Hydrogen / Gas Turbine 40% 1.21 kg/kWh 1.18 kg/kWh
The method use to calculate the above numbers has undeniably been rough and ready, but they do reflect what Horizon believes to be the reality of the situation – that the weight difference between gas turbine and battery power is of the order of 10:1, and that the energy advantage of hydrogen over synthetic kerosene is not sufficient to overcome the disadvantage of hydrogen’s high storage weight. The deadweight numbers are also in the gas turbine’s favour as a lower dead weight results in a better fuel and structural efficiency for the aircraft. Other manufactures would undoubtedly come up with different numbers because they do reflect a company’s technology and way of doing things, such as achieving a Category A certification.