Methane beats hydrogen in our energy future

The hope that the hydrogen economy will provide a solution for our future energy is misplaced, says Paul Bieleski, a retired chemical engineer and ‘born again’ scientist from Nelson.

A hydrogen future as suggested in the Spring 2008 issue of Energy NZ magazine is a faith-based answer, which is not supportable by current scientific knowledge, has many disadvantages over the medium of electricity, and is dependent on yet un-resolved technical developments.

The current method of making hydrogen from methane at about 72 percent efficiency is costly in energy usage, so that if hydrogen is derived from methane and used in cars, it will produce more pollution in the form of carbon dioxide and nitrogen oxides than if the methane was used directly as CNG.

No matter what the pressure and temperature, methane contains more hydrogen and more energy than pure hydrogen itself, and hydrogen produced this way will not be pure enough for fuel cells.

In addition, because of its low molecular weight, hydrogen storage requires a much higher standard on seals to prevent hydrogen leakage. The low temperature of liquid hydrogen will freeze air if there is a leak and a small level of evaporation is unavoidable, and so requires venting. In comparison, the technology for methane storage is simpler and well established.

To compress hydrogen to 700 atmospheres, a multistage compression process is required, consuming about 15 percent of the energy content.

Liquefaction would require something like 30 percent of the energy content.

The pumping cost for hydrogen pipelines can be expected to be lower than for methane pipelines, because hydrogen has a low viscosity, although we have no estimates for any advantage here. However, the standard of piping required is much higher as hydrogen has a tendency to make metals brittle which makes hydrogen pipelines much more expensive.

The extraction of hydrogen from coal as an energy source would be problematic because this process will produce even more carbon dioxide than the process of producing methane from coal. Hydrogen produced from coal would require extra processing to make it pure enough for fuel cell use, and we have yet to see how much energy will be required to sequester carbon dioxide underground in serpentine rocks if this becomes feasible.

Production of pure hydrogen from large photo voltaic panel arrays is proposed as a way of capturing the peaks of solar energy for storage. This would not be necessary in New Zealand as it would be more energy efficient to use such electricity in the grid and save the energy as water held back in hydroelectric dams.

Producing hydrogen by electrolysis is done at about 70 percent efficiency and is therefore going to waste energy. The second law of thermodynamics is the reason behind the fact that conversion of an energy source to the intermediate medium of hydrogen is uncontrovertibly a wasteful step. This would indirectly produce carbon dioxide emissions because some electricity is produced from fossil fuels. The thermodynamic efficiency of hydrogen fuel cell production of electricity at 70 percent is the same as its production. That results in half the original energy to be wasted. If the hydrogen was used in internal combustion engines, the waste will be even greater.

There is a belief that in the future motor cars will be driven by hydrogen powered fuel cells, however the fuels cells remain very expensive and have yet to be produced with a long enough life and it is a very dubious technology. The promises for the arrival of a production Ballard fuel-cell motor car has not been met, in spite of well-funded research. They usually turn out to be large, heavy and expensive. The long-term reliability and life span is somewhat doubtful and it would be better to try and develop a methane powered fuel-cell.

To transport hydrogen by road tanker will require expensive canister trucks that would weigh some 40,000 kg and carry only 400 kg of hydrogen, or enough to fill 60 cars, while the same size truck carrying petrol could fill about 800 cars. The ELOT (energy loss on transport) for this form of transport would approach 100 percent per 1000 kilometres. The transfer of liquid hydrogen to cars will also require a complex fuelling system that would require specialised equipment and operatives.

For these reasons I think hydrogen has no place as an energy solution.