The future of hydrogen fuel

When I was very young, our gas stove
ran on town gas. I didn’t know it at the
time but it was a mixture of hydrogen and
carbon monoxide produced from coal.

One day a serviceman came round
to change the nozzles on our stove and
gas heater, and very quickly our house,
and eventually the city, were converted
to natural gas (methane). It was a leap
into modernity. 

Not only did it eliminate
pollutants emitted during gasification, it
promised a seemingly unlimited supply of
clean burning methane from offshore gas
fields.
But that was in an era where “clean”
meant “free of the toxic chemicals and
particulates released by coal gasification”.
Today, clean also means free of carbon
dioxide.

As the global community works
to decarbonise its electricity supply, one
of the biggest remaining sources of carbon
dioxide emissions will be from burning
methane for heating and cooking. In a
back-to-the-future step, many futurists are
contemplating a variation of town gas –
pure hydrogen.

Today, most hydrogen is produced
from fossils fuels, emitting large quantities
of carbon dioxide as a by-product, so that’s
no help. But there’s increasing interest
in producing it from pure water. In a
well-known process called electrolysis,
excess electricity from wind or solar farms
is passed through water to crack it into
its atomic constituents – hydrogen and
oxygen.

When the hydrogen is used for stoves,
or space heating, the only combustion
product is water vapour! So what’s
standing in the way of this utopian fuel?
Problem one is that producing
hydrogen from electricity is only 70%
efficient, so you need a very cheap
electricity supply. It could be coming.

As
our electricity is increasingly sourced from
wind and solar, the amount available will
often exceed the electrical load. Owners of
the generators will seek an economically
worthwhile purpose for this excess, such as
charging batteries, desalinating water, or
making hydrogen.

Instead of burning
the hydrogen, an
alternative use
would be to use it
to store energy, like
in a battery, then
regenerate electricity
in a turbine generator
or a fuel cell. 

Problem two is that the current large-scale
electrolysis units are so expensive
that the cost of producing hydrogen is
several times more than natural gas.
But one thing we know for sure is that as
manufacturing volumes increase, costs
come down. We’ve seen it already in
related industries.
Wind turbine prices have halved
in the past five years and solar prices
have dropped even faster. Similar cost
reductions are likely for electrolysis units.

Problem three is that steel pipes – a
major part of the current gas delivery
infrastructure – aren’t suited to
transporting hydrogen. They become
brittle because the hydrogen molecules
work their way into the spaces between
the iron atoms and eventually cause cracks
to form.

Fortunately, modern piping used
for gas distribution is mostly made from
polypropylene and does not suffer from
this problem.
Hydrogen can be mixed at up to 10%
with the methane in the existing gas
distribution network without any risk of
corrosion nor need to change the nozzles
on stoves or space heaters. Above 10%
hydrogen concentration it’s easier to
commit and convert all gas appliances to
run on pure hydrogen.
The city of Leeds in the UK has a plan
to do this in the late 2020s.

Instead of burning the hydrogen, an
alternative use would be to use it to store
energy, like in a battery, then regenerate
electricity in a turbine generator or a fuel
cell. But it makes for a very inefficient
battery.

The round-trip efficiency – electricity
to storage medium and back to electricity
– is about 35%, much worse than the 90%
efficiency of a lithium ion battery. So this is
a less attractive use for the hydrogen than
using it to replace natural gas in our cities
for space heating and cooking.

If we can successfully make the
transition to hydrogen for heating and
cooking we will have a winning fuel that we
can keep using literally forever.

The main
impediment today is cost.
I used to be sceptical that hydrogen
use would become widespread, but given
the rapid rate of reduction in the price of
renewable electricity, and a reasonable
expectation that the price of electrolysis
will continue to fall, the economics might
indeed work out.