Page 45 - Energize April 2022

VIEWS AND OPINION

concept, that of cheap surplus electricity. The production of one cubic metre of hydrogen, corresponding to an intrinsic energy
A useful piece of accounting fiction of 3 kWh, requires 5 kWh of electricity with a high efficiency industrial electrolyser,
suggests that the incremental or marginal (around 60%). Media reports abound with claims of new and improved electrolysers with
cost of renewable energy is zero. This higher efficiency, but none has reached marketable stage, and the figures given should be
stems from the fact that the lifecycle considered reasonable for the state of the art. It is also common practice to include heat
cost of RE is almost wholly capital, and production in the efficiency calculation, which gives much higher figures. But heat is of no
there are no operating costs. Increasing interest to the storage of electricity and should not be included.
production (above a contracted amount) One of the primary areas under consideration is hydrogen as a fuel. Electricity generation
incurs no extra cost and is supposedly free. using green hydrogen is an interim market, involving replacement or conversion of existing
Of course this is pure fiction as the cost gas-fired plant to hydrogen-fired, but is a convenient market for surplus electricity. In the
of production is carried by the price of long term, the surplus production problem will still exist, but hydrogen-fired turbines might
contracted electricity, but the idea is being be used as a balancing mechanism to cater for low production. However, the efficiency of
used to promote green hydrogen. an open cycle turbine is around 30%, so the overall conversion efficiency from electricity
to electricity (EtE) will be around 20%. The alternative use is fuel cells which also have an
The drive for green hydrogen appears to electrical efficiency of around 50%, (discounting heat produced) giving an EtE efficiency of
have three components: around 30%.
• Surplus electricity requiring another Hydrogen powered vehicles, with either converted internal combustion engines or
market (i.e., non-electrical) fuel-cell-based electric vehicles are at production stage. Hydrogen is seen as a promising
• The need to replace fossil-fuel-based alternative to batteries for large vehicles such as trucks and busses and is also being
vehicle fuel with some other liquid considered for marine propulsion, either directly or in the form of hydrogen carriers. Green
fuel. hydrogen has been proposed as a replacement for domestic and industrial natural gas.
• An alternative to battery power for Technologies for hydrogen storage and transport are well developed.
transport: There is no doubt that the Hydrogen storage of electricity using electrolysers and fuel cells has a turnaround
electric driven vehicle is superior to efficiency of 25 to 30%, which means that approximately a quarter of the electricity
the petrol or diesel driven version. produced is available from the storage, and hydrogen is not seen as an economic means of
But there are problems in that storage storing electricity.
of energy is in a heavy and expensive There is an opinion that green hydrogen should only be used for applications where
electrochemical battery. electricity is not suitable. If all the above applications are realised, it is unlikely that the
amount of hydrogen produced from surplus RE electricity will be sufficient to meet demand,
Surplus electricity (barring inter-grid sales) and RE or low carbon plant dedicated to the production of green hydrogen will be required.
cannot be used in the grid or stored, so There are already plans to use a large solar PV plant for hydrogen production in the Middle
needs another market. If this surplus could East. Other sources of energy that could be used include nuclear power. This however
be used to produce a saleable product changes the cost structure, as this energy is not free, and this will need to be taken into
for which there is another market, the account when considering such projects.
problem is solved. Hydrogen provides a
solution as it can be easily produced by References
electrolysis, is useful as fuel for transport 1. A Merlin: “Low-carbon hydrogen: for what uses?”, CIGRE Electra N0. 320, February 2022
and other purposes, and can be used as a
feedstock in the chemical industry. Despite Send your comments to rogerl@nowmedia.co.za
the advantages of green hydrogen, there
are challenges in its production, storage,
distribution and re-usage.
The hydrogen production process
which is currently attracting a lot of
interest, is electrolysis, or hydrolysis
of water. Despite developments in the
field, this process is still expensive and
inefficient, factors which are expected to
be overcome in the near future.
Water electrolysis is a technique
that has been known for a long time.
It has made great progress in recent
times thanks to increasingly efficient
electrolysers, but the electrical efficiency
is still low.

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