WHAT IS THE CHALLENGE?There is a growing awareness in society that fossil fuels as used today must be replaced with renewable more environmentally friendly alternatives. In many respects, hydrogen gas is the ultimate alternative, it can be created by splitting water into oxygen and hydrogen with many clean renewable energy sources and when used the byproducts are energy and plain water again. The retrievable energy can be used in conventional combustion, powering cars, heating houses, etc. or be used together with fuel cells to produce electricity in large or small scale. Hydrogen has a very high energy content per kilo, almost three times higher than gasoline.However, there are some fundamental problems related to the use of hydrogen. The diffusion rate through most materials is quite high, as the hydrogen molecules are very small, hydrogen embrittlement, etc. resulting in a lack of suitable efficient storage technologies. It is the most lightweight of all gases, resulting in large volumes when stored in compressed form even if the pressure is very high. Hydrogen forms easily highly combustible mixtures with air, and as it also is a colourless and odourless gas it is undetectable by humans, the result of this is high handling and risk management costs. The problems prevent a common use of the gas.
A lot of research is going on worldwide in order to find the best method to store and transport hydrogen, in metal hydrides or other chemical compounds, etc. Today there are only two methods in practical use, at least for mobile applications, to store it in large high pressure tanks or in liquid phase at cryogenic temperatures, none of them are very good.
HOW CAN THE PROJECT CONTRIBUTE TO A SOLUTION?
Two ideas form the MacroSphere concept, the distributed tanks idea and the integrated gas handling chip idea. Advanced Micro System Technology (MST) is the key enabling element in the gas handling chip. Hydrogen is stored under high pressure in a large number of small autonomous sub-tanks, the MacroSpheres. The difference between internal and external pressure controls the gas flow to or from the MacroSpheres. A gas handling micro chip is mounted inside each sub-tank, which has the size of a golfball. The system combines the best storage performance available with focus on a convenient and non-dramatic handling for the user. Some system highlights are presented in the following.
Storage capacity, the system storage capacity has the potential to be the highest achieved so far. Spherical tanks have by definition twice the pressure resistance compared to otherwise identical cylindrical alternatives, such a tank had the world record of 11.3 wt% a couple of years ago. The exact storage capacity is difficult to estimate as it depends on many parameters such as safety factors, lifetime (i.e. number of pressure cycles), acceptable cost having an impact on the quality of the fiber composite, etc. Given some realistic assumptions on the system requirements, the storage capacity in wt% is estimated to be between 10 to 20 wt%, the lower percentage will give a very robust and failure safe system.
Mitigation of handling risks, the method to store gas in a large number of small autonomous composite tanks instead of a few large pressure vessels mitigates risks in handling in several aspects. First, there is no handling of high pressure fittings or other components, which can cause a risk if mistreated or worn out. Second, in vehicle applications, several factors limits the possible damage caused by the hydrogen gas stored in MacroSpheres, in case of an accident. One factor is that it is a distributed system with no physical connections between the individual spheres. This means that, if the buffer tank is destroyed, the Hydrogen MacroSpheres will be spread all over the area. Many still unharmed and as they then are in ambient pressure, they become leak tight and can be safely collected.
Low operational costs, the idea with a return and refill system dramatically reduces the operational costs. The possibility of refilling the tanks hundreds of times has a huge impact on the operational costs over the system lifetime.
WHO WILL BENEFIT FROM THE RESULTS?
The concept is a good example of the effect of “disruptive technologies”. Advancements in one technical domain can suddenly generate a breakthrough in a completely different area. In this case, the system engineering progress in MEMS or Micro System Technology has generated a completely new approach for efficient hydrogen storage with an unprecedented storage capacity of minimum 10-15 wt%. The absence of high pressure components and interconnections will also have a huge impact on the consumers view on gas storage and handling in the future, as the, in many cases unjustified, fear for high pressure storage will disappear, as the user never has to be confronted with any problems related to the same.
Not only individuals, but the whole society will greatly benefit, if the project can contribute to a common use of a clean renewable energy carrier, such as Hydrogen.
