Alternative Energy Sources

Hydrogen

While the fossil-fuel era is entering its sunset years, a new energy regime is being born that has the potential to remake civilisation along radical new lines...It produces no harmful CO2 emissions when burned; the only by-products are heat and pure water.*

These are the sort of statements that are commonly seen these days about the 'hydrogen economy'. While not exactly false (except possible the first sentence), they give a false impression about the uses and cleanliness of hydrogen. What is the truth about this marvellous new 'fuel'?

First of all, hydrogen is not a fuel such as oil, coal or electricity; it is an energy carrier, rather like a battery. Although hydrogen is the commonest substance in the Universe, it does not exist as a free gas or liquid on Earth so it has to be produced. For this you need two things, a hydrogen source (akin to a metal’s ore) and an energy source to separate the gas. It is this energy source that is one of the major problems with hydrogen: the hydrogen-powered fuel cell in your car might appear to produce no pollutants but did the original energy needed to fill the cell?

Production

As mentioned, hydrogen creation needs a hydrogen source and an energy source. At the moment, most hydrogen is produced from natural gas which acts as both sources. Unfortunately, because something is lost whenever one form of energy is converted to another, the hydrogen produced has only 50% of the energy value of the original gas. And, since the problem we are facing is the depletion of fossil fuels, using gas to create hydrogen does not seem very sensible.

The alternative to this is to use electricity to split water into hydrogen and oxygen. If that electricity comes from fossil-fuel powered generators, then we are no better off that the system above. But if the source of the electricity is from renewables or nuclear, then we have the potential for a cleaner fuel for transportation. Unfortunately much energy is lost in the process, so the hydrogen that comes out has about 70% of the original electricity.

Storage and Distribution

Hydrogen is 2700 times less energy dense than petrol so it needs to be reduced in size before storage and distribution. There are three ways of doing this: compression, liquefaction and chemical-combination.

• Hydrogen is the hardest gas to compress and the efficiency is about 55%. It requires extremely strong and heavy tanks to store.
• Liquefaction is better in that it does not need such heavy tanks (although it still takes up three times the volume compared with petrol) but its efficiency is about 40% at best. Also, some liquid hydrogen inevitably escapes from storage at the rate 3-4% a day for cars, so every minute that you were not driving your car would be costing you money in lost fuel.
• Chemical-combination means mixing the gas together with metal hydrides which act as a sort of sponge. The efficiency is about 60% to produce the hydrides without taking into account the losses from producing the initial electricity.

Delivery of both compressed and liquefied hydrogen would be troublesome. If by road, it would require 13% more tankers so about 1 in 7 lorry accidents would,on average, involve a tanker. If using pipelines, it would take 1.5 times more energy to transfer hydrogen 3,000 km then is contained in the gas itself.

Summary

The principal hope for hydrogen is that it will be a replacement for oil as a fuel for transportation. But, compared to electricity, it generally loses out in most areas.

• In production, it is a clear loser since we would have to create that electricity to produce the hydrogen in the first place. If you are generating electricity, it is better to use it directly and make better use of the 30% that is lost to separate the hydrogen.
• For distribution, electricity has one of the most efficient methods of energy transfer known – up to 90% efficiency. Whatever method you use to transfer power through hydrogen, the efficiency is likely to drop to about 30%. The infrastructure for electricity transfer already exists while that for hydrogen is, at the moment, almost non-existent. The systems for creation, storage, transfer and supply (to users) would have to be built virtually from scratch over the next couple of decades, enough to cover whole countries.

As far as motor transport is concerned, while we have relatively cheap fossil fuels, the best option would be to use hybrids (vehicles equipped with both internal combustion engines and electric motors) for cars and lorries to reduce the oil used and extend its useful life, while using pure electric vehicles such as trams and trains for mass transport. By the time we have run out of available oil and gas, we are likely to be so short of electric power that we could not afford any unnecessary wastage. By then, I suspect, personal public transport, if it exists will have two wheels or four legs.

* From "The Hydrogen Economy" in "The Environmental Magazine" January/February 2003 Vol. XIV, no. 1

Have a look at the page on efficiency for more information.

Most of the data in this section comes from “The Future of the Hydrogen Economy” and "Fuel Cell Folly". They can both be downloaded below.

Unconventional Oils : Natural Gas : Coal : Nuclear : Renewables : Hydrogen