Alternative Energy Sources
Main final use form:
carrier for electricity
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
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
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
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
- 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
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.
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,
Have a look at the page on efficiency for
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.
Oils : Natural Gas : Coal
: Nuclear : Renewables
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