The path to hydrogen has 3 components. 1 Increasing the efficiency of production. The 45% efficiency quoted by wazoox is low, IMHO, and may have been caused by

The path to hydrogen has 3 components. 1 Increasing the efficiency of production. The 45% efficiency quoted by wazoox is low, IMHO, and may have been caused by driving the electrolysis cells at high currents, where they depart from reversibility. Lab cells that operate in a reversible manner get close to 100% - sadly at a low rate of production. Work needs to be done to get this higher at large rates of production. That said, inductrial production of hydrogen is often done by high temperature dispoportionation reactions, where the hydrogen is extracted. These are often done in large refineries where excess byproduct process heat is involved and many other products are made. Cold loops are used to get the hydrogen and it can also be extracted by metallic diffusion of hydrogen through thin membranes of palladium and sillver. Sadly, these both use energy only available as wasted process heat in hydrocarbon refineries - which are expected to decline in time and eventually become unavailable as the carbon economy declines over the next ~~100 years. 2 Storage costs. wazoox is correct. Compression to 2000+ PSI wastes a large part of the energy via the irreversibility of the reverse Carnot cycle. An IC engine gets power running a carnot cycle forward. 30% lost is quite believable. As liquid hydrogen in high efficiency low loss super-insulated tanks. These tanks lose hydrogen as heat gets in and boils it off - as long as you use the boiled off hydrogen as fuel cells fuel, this does not matter. You also need to add heat to feed gas to the cells, usually heat from the air works as long as it is designed to avoid frost blocking the atmospheric side.Hydride storage is another. Hydrogen forms clathrates - a crystal of organic material with hydrogen trapped atomically. It takes energy to make and energy to recover the hydrogen - 15-20% lost?? 3 The fuel cells. As in electrolysis, labs cells can be close to 100%. Hard driven cells are a lot less. Work needs to be done to get above~~95%. The warming of the earth is the gorilla in the room that holds the earth in its grip. This must be solved. Altentate means to make energy, solar, wind, tide, nuclear can do this - we must do this or the earth as we know it may well vanish, with huge loss of all species of plants and animals - one of which is man!