Existing solutions
Considerations on hydrogen
Hydrogen is:
- the simplest atom form (1 electron, 1 proton)
- the lightest and most abundant element in the universe (combined with oxygen in water and with carbon in hydrocarbons)
- ...and has the highest energy density per kilogram in comparison with other combustible fuels, particularly natural gas.
Although hydrogen has a very high mass energy density, the fact that it is a very light gas makes its storage and transportation real challenges. The aim of hydrogen storage technologies is thus to reduce the volume that hydrogen naturally occupies in its thermodynamically stable state under ambient conditions.
Historically, storage methods have been based on compression and liquefaction (direct storage), which are now established and efficient approaches, but they involve huge problems of safety and the associated costs of compression work and cooling are non-negligible.
More recently, several alternative approaches based on solid-state storage have been under intensive investigation – McPhy’s technology being one of them.
Gas storage
For practical storage, gaseous hydrogen must be pressurized to several hundred atmospheres and stored in a pressure vessel or tank (made of steel or composite material).
Major issues:
- Poor volume density
| Fuel | Energy density (kWh/l) |
|---|---|
| Hydrogen | 2 (to 700 bar) |
| Natural Gas | 3 (to 200 bar) |
| Diesel | 8 |
- Safety (real or perceived)
- Energy expenditure required for compression (uses 10 to 25% of gas energy content)
Liquid form storage
Storage in liquid form is even more expensive. It requires significant investment and substantial facilities for the liquefaction process, conservation and making it operational in liquid form at 20 Kelvin (-253°C !). This form of storage is used for very particular applications.
Solid storage
The third and very promising alternative is to store hydrogen in the form of metal hydrides which have been under intense scrutiny for many years, offering safe, reversible hydrogen storage, with an excellent energy efficiency (no compression).
As of today, McPhy’s technology and products offer the most relevant economical and technical solid-state hydrogen storage solution.