Hydrogen and tidal energy
Hydrogen and tidal energy
by Neil Kermode (2017)
(IET
Engineering and Technology Reference, pp. 1–10,
doi:10.1049/etr.2016.0163)
Kermode
analyses renewable energy in the Orkney Islands, where production
exceeds the needs of the local population. The situation of the
islands provides abundant energy from wind, wave, and tidal stream
[1]. The paper concentrates on tidal production, the output of energy
from underwater turbines, and the development of strategies to
utilize it.
Tidal
flow fluctuates due to the rotation of the earth and the movement of
the moon in its orbit. The daily ebb and flow of the tides gives
peaks in water speed at roughly twelve hour intervals, but these
peaks are greatest on the ‘spring tides’ which occur at intervals
of approximately fourteen days, and least on the intervening ‘neap
tides’. The power produced by tidal stream turbines increases as
the cube of water velocity. No power is generated during those hours
when there is negligible movement of water (slack water), and because
peak water speed at spring tides is about twice that at neap tides,
roughly eight times as much power is generated during spring tides as
during neap tides.
An
obvious solution to the problem of having more renewable energy than
is needed locally would be to export it to the Scottish mainland for
distribution on the UK grid (to avoid possible confusion: the largest
of the seventy or more Orkney Islands is known as Mainland). Kermode
explains that while there are connections between the islands and
mainland Scotland by cables under the Pentland Firth, the historical
development of the electricity grid in the UK means that it is
efficient only when used as originally planned – in this instance,
when sending electricity from the Scottish mainland to the Orkney
Islands, but not the reverse. [2]
Options
for storing energy to use during periods of low tidal production are
examined: few methods can handle large quantities for several days, and one contender, hydroelectric pumped storage, is ruled out by the local geography. The
case is made for developing a system based on the production and
storage of hydrogen. The gas can be produced by the electrolysis of
water and then stored. While there are many uses for hydrogen, for
example in the regeneration of electricity, the chemical industry and
transport, the financial return varies widely from one application to
another, and with local circumstances. Twenty of the Orkney Islands
are inhabited, and they depend on a network of ferries, which have
varied energy needs both at sea and in harbour. Application of
hydrogen to the ferry service was considered the most promising use
of the gas, and a staged integration of hydrogen fuel was planned. To
this end the European Marine Energy Centre installed an electrolyser
and gas storage facilities on the island of Eday, where use can also
be made of wind power if needed.
The
paper contains valuable detail and background information, as well as
many useful references, but does not appear to be available on open
access at present. A recent web publication does however give an
update on the use of hydrogen in the ferry service [3].
[3]
UK’s first marine hydrogen injection system funded for
Orkney ferry
Stuart
Nathan 8th October 2018
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