Memorandum submitted by Professor S Forbes
My practical expertise is in the field of Industrial
Refrigeration and I am a professional engineer, holding the degrees
of BSc, PhD, ARCST. I am a Member of the Institution of Mechanical
Engineers and a Fellow and past-President of the Institute of
Refrigeration. I am, at present, Chairman of the Technical Committee
of the Institute of Refrigeration. I am a Visiting Professor of
Mechanical Engineering at the University of Strathclyde.
1. The United Kingdom is one of the best
areas in the world for the exploitation of tidal stream power.
2. The tidal stream resource is very large,
much greater than wind resource.
3. The principle of extracting power from
tidal streams has already been demonstrated by small-scale trials
in Scotland, Japan and Australia.
4. Economic use of tidal stream power depends
on using the largest possible turbines in the fastest available
5. Industry will not develop tidal stream
turbines while the cost of fossil fuel is so low.
6. Governments cannot afford to increase
the cost of fossil fuel.
7. The fundamental technology of tidal stream
turbines is well understood.
8. It is not more research which is needed
but finding for design and construction of large tidal stream
9. Funding is also needed for a careful
examination of the tidal stream resource, which has not been accurately
10. Allocation of all possible sites for
tidal stream turbines should be discussed and agreed with all
interested parties as soon as possible. The restrictions to be
imposed when the sites are brought into use should be agreed in
1. My interest in the potential of tidal
stream power is strictly as an informed amateur. However I was
involved in the development of freezing fish at sea (probably
one of the sources of our current fisheries crisis) and I have
sailed in trawlers to the Hebrides, Orkneys, Shetlands, Faroes,
North Norway Coast and Bear Island. I have therefore some experience
of the power of the sea as manifested in winds, waves and tides.
I have also lived for most of my life on the West Coast of Scotland.
I am also interested in sailing.
2. I should perhaps also mention that I
am a founder Director of Star Refrigeration Ltd. Which is the
leading industrial refrigeration firm in the UK and notable for
innovation and sound engineering. I am the President of that company
and a major shareholder in it.
3. My interest in tidal stream power dates
back for a few years to the time when I was handing over responsibilities
at Star Refrigeration Ltd. to the younger generation and looking
for something interesting and useful to do. It was obvious that
there is a huge potential for energy extraction from the tides
around the UK coasts. The puzzle was why it was not being done.
4. Some preliminary calculations were done
which seemed to indicate that over 20 per cent of the UK electrical
requirement could be provided from tidal stream power. It was
a great surprise to me when the Twenty-Second Report of the Royal
Commission on Environmental Pollution "EnergyThe Changing
Climate" seemed to contradict that view. The report stated
(7.96) "The amounts (sic) of energy it is practicable to
obtain from tidal streams and shoreline wave energy seems likely
to be quite modest". It seemed obvious to me from practical
experience that this conclusion was wrong. I then began to seek
out the facts on which the Royal Commission conclusion had been
5. I found that DTI had commissioned reports
on tidal stream power in 1989, 1993 and 1999. It was from the
1999 report that the Royal Commission Report formed its conclusion.
The 1999 Report, ETSU R-122 pp 137-145 concludes "The prospects
for conventional tidal stream technology in the UK appear limited".
On examining the 1999 Report and the 1993 Report (which was a
more impressive document), I found that they had significantly
underestimated the power available and had consistently overestimated
the likely cost.
6. It is obviously not possible for a private
individual to calculate the power available from many individual
sites so I decided to study one well-known site, the Gulf of Corryvreckan.
Figures of mean spring and reap tidal stream velocities were available
from Admiralty charts as were the depth contours and dimensions
of the gulf. Corryvreckan is about a mile wide and over 100 m
deep for about half its width. Tides are quoted as running at
up to 10 kn. In my initial calculations, which were done from
first principles because I had not then obtained much in the way
of literature specific to tidal streams, I proposed that an underwater
barrier should be placed across the gulf at its narrowest point
to increase the velocity by reducing the depth to 50 m.
7. The 1993 ETSU report, ETSU T/05/00155/REP
also quotes an average power output for Corryvreckan. In 1996
the European Commission published a report through DGXIII on "The
exploitation of marine currents", Report EUR 16683 EN. This
is a much more practical report than the 1993 ETSU report and
it also gives figures for possible power production from Corryvreckan.
Both the ETSU and the EU reports produce the power generation
by employing a "farm" of turbines covering the area
of high stream velocity. This is different from my method which
intensifies the velocity and uses a single row of turbines which
I think would be much cheaper.
For purposes of comparison I calculated the
power available at Corryvreckan using a farm of turbines and assuming
the same efficiency as had been assumed in the EU Report. There
are therefore four figures for power production at Corryvreckan.
|No. of Rotors||Installed Capacity|
|ETSU (Table 6.3)||5
|EUR (Summary Table/1)||?
8. I have applied for a patent on some novel methods
of power generation from tidal streams and it includes the method
of intensification. I have had the calculations for the intensified
systems checked by several competent engineers who confirm that
my figures are broadly correct. I have no idea why my figures
differ so much from the "official" figures but I do
not believe that my figures can be wrong by several orders of
9. It is probable that official figures for other sites
are not wrong to the same extent as the figures for Corryvreckan.
For example, the rated power at Kyle Rhea and the Dorus Mor are
given as 32MW and 194MW in EUR 16693 EN both have much less potential
than Corryvreckan. The figures for Corryvreckan are just wrong!
10. I shall try to answer the specific issues which you
have been charged to cover. I do not wish to discuss wave power
in detail beyond saying that there is awesome power in storm waves
but I very much doubt that it can safely be harnessed.
11. Technological viability
Equipment is not at present available for efficient large
scale-generation of power from tidal streams. This is because
it has not been designed and tested. The principle of tidal stream
generation is sound and has been proved. There is nothing highly
technical in the design but, to be efficient and effective, the
equipment must be designed on as large a scale as possible. The
cost of design will be high so individuals cannot undertake it.
It must be done by partnership between government and industry.
I shall return to what requires to be done after I have dealt
with all the other issues.
12. Commercial viability
Judging by the example of wind power, tidal stream energy
will become commercially viable after large scale designs have
been proved. Tidal stream power is theoretically much more attractive
than wind power. Much more power can be generated from the same
size of machine. The tidal stream generator will be submerged
and therefore not an eyesore. The submerged tidal stream generator
will not be subject to storm or wind damage and will not have
to be designed to withstand the severe overload conditions to
which wind turbines are subjected.
Sub-sea technology has advanced in recent years but neither
the oil companies, who are the main experts, nor the electricity
companies, who have excess hydro and nuclear capacity in Scotland,
have any present motive to develop tidal stream power.
13. Current Projects
The only project that I am aware of is one funded by an EU
grant for a 300kW post-mounted turbine to be sited off the North
Devon coast. The turbine will be designed and provided by Marine
Current Turbines Ltd. This is a worthy project but it is too small.
Marine Current Turbines, for sound commercial reasons, plan to
increase the size of their installations step by step. This will
take a long time and will tend to restrict the diameter of turbines
which will be designed. I am not aware of any past projects which
failed. They were all very small because of limited resources
and they were all taken out of service after they had proved the
soundness of the principle. A case in point is the Corran Narrows
turbine which produced its design power of 15kW without turbine
problems. Most of the work was funded by Scottish Nuclear, who
have never published a report, and who have a surplus of pollution-free
power and other problems. As far as I know the Canadian, Japanese
and Australian projects all produced power as they were intended
to do but they were very small. What is needed is financial support
for a full-scale project with a turbine as large as can be designed
14. Renewable Strategy
We need all the renewable power which can be obtained at
reasonable cost. I am agnostic about the viability of wave power
because of the extreme conditions for which the devices will have
to be designed.
Tidal stream energy is a huge resource which could be exploited
over the course of a few years if design and prototype costs could
be funded. There are many design challenges but they do not take
us into any really new technology. In my opinion tidal stream
energy should be given top priority by government.
15. Research and Development
Very little research and development is being undertaken
at present which is not surprising given the conclusions of the
Royal Commission of June 2000 and the ETSU Report of 1999. Most
people would take these at face value.
I do not think there is a great need for fundamental research.
Even assuming turbine efficiencies lower than those being achieved
by wind turbines, there is still a vast amount of power available.
The urgent priority is to get large turbines working. A certain
amount of development would go hand in hand with the design and
testing but wind turbine experience can be used to design tidal
stream turbines which, of course, have to be much stronger. In
my opinion we should start designing and building a large turbine
now, making use of existing knowledge. We should not look for
perfection but for a big, robust machine which works.
The only peer review which is of any importance is the examination
and testing which the ocean will provide.
16. Environmental aspects
I do not think that either wave or tidal stream generators
would have any significant effect on marine life. Large tidal
stream generators would rotate at only three or four revolutions
per minute and would be static. High-speed pleasure boats are
potentially much more damaging.
Marine life in the form of weed and barnacles would have
a significant effect on tidal stream turbines. Anti-fouling measures
would have to be taken as they are on every ship.
Tidal stream turbines and merchant shipping cannot co-exist
in a restricted area. Small pleasure craft would not be a problem
because the turbines would be submerged by several metres. The
area of turbines would have to be buoyed and entry of merchant
ships, fishing and naval vessels restricted. This should not be
a great inconvenience because the sea is very large and alternative
shipping routes could be specified. Many of the best locations
for tidal stream power are at present designated "Submarine
exercise areas" but, no doubt, matters could be arranged.
17. International comparisons
Britain is at present a world leader thanks to the enterprise
of private companies like Marine Current Turbines. I am not aware
of ongoing research by other nations. Obviously the EU has given
a lot more support than UK government but even the EU support
UK is one of the best placed countries to exploit tidal stream
power because of the shape of our coastline and our proximity
to the continental shelf. Other countries with strong tidal streams
include France, Norway, Japan, Canada, USA and Chile/Argentina.
I would be surprised if the Japanese were not carrying out
some useful research bearing in mind their lack of indigenous
energy sources. A literature search produced many Japanese papers
but no evidence of current large-scale projects. I would expect
any large-scale Japanese project to be kept confidential for as
long as possible in order to allow them to build up a technological
18. Costs and Benefits
The cost of the actions proposed in the following paragraphs
runs into many millions of pounds but these costs are very small
compared to the costs which can be attributed to environmental
19. Actions Needed
Survey of the resource
It is fairly obvious that the tidal stream resource is very
largemuch larger than the wind power resource even allowing
for the siting of wind farms at sea. Unfortunately the size of
the resource and the details of its position are not known. Recent
work, such as EUR 166683 EN "The exploitation of tidal
marine currents" 1996 and ETSU T/05/00155/REP "Tidal
Stream Energy Review" 1993, differ widely in the size
of resource allocated to the same sites. This is partly because
of different methodologies but more because of differing estimates
of the gross power in the tidal streams.
The main source of information on tidal stream velocities
is the Admiralty Chart and the Admiralty Tidal Stream Atlas. Unfortunately
these were prepared for navigation and often do not show tidal
stream velocities at the positions which would most be suitable
for the generation of power. The tidal stream atlases are also
difficult to quantify because the velocity of the tidal streams
is indicated by the size of the arrow rather than by figures in
It is probable that the Admiralty has raw data from which
the tidal stream atlases were prepared. If so it should be possible
to get reliable figures for tidal stream velocities. This should
be investigated as a matter of urgency.
The Admiralty data, some of which goes back to the days of
sailing ships, should be supplemented by a modern detailed survey
making use of satellite positioning and echo sounding of the sea
bed. The nature of the sea bed is important whether the turbine
is to be post mounted or anchored in position. The modern survey
could occupy a large survey vessel and crew for several years.
This work should be carried out while prototype large turbines
are being designed and constructed, not after.
Negotiation of locations
Locations for the siting of UK tidal stream generators will
all be within the territorial waters of Great Britain and on the
continental shelf. The conflicting interests of commercial shipping,
fishing and Naval forces (mostly submarines) will have to be resolved.
It will almost certainly be necessary to close certain areas to
shipping and to restrict access to narrow lanes in others. This
should not be a major problem provided the Government is prepared
to adjudicate firmly.
Preliminary work for preferred tidal stream sites should
start as soon as possible, involving all the interested parties
from the first.
Tidal stream velocities are strongly affected by the shape
of the sea bed and the shape of adjacent land masses. The strongest
tidal streams occur round headlands where the tide is flowing
from one part of the ocean to another, in straits and gulfs through
which the tide flows and especially where a shelving bottom causes
velocity to increase to conserve the momentum of the stream. Examples
include the Bay of Fundy, Corrievreckan and the Bristol Channel.
In some cases the natural frequency of the water in the region
is tuned to the forcing frequency, giving rise to remarkably high
velocities. The Bay of Fundy and the narrows at Kyle Rea are examples
of this phenomenon.
Power available from a turbine varies as the cube of the
velocity. If the velocity can be doubled the available power increases
by a factor of eight. It is therefore vital to make use of velocities
which are as high as possible.
It has been proposed that the shape of the sea bed should
be modified in regions where tidal stream velocities are already
high, to increase the velocity still further. A way of doing this
is by the creation of artificial underwater reefs. These can be
used either to decrease the cross-sectional area of the flow or
to deflect flows into preferred areas. This is a much cheaper
and less environmentally damaging method than the construction
of tidal barrages. The reefs would be underwater all the time.
"Barrier" reefs to decrease flow area would be submerged
significantly more than the turbine diameter. "Deflector"
reefs to deflect tidal stream flow would approach the surface
more closely but could be kept below keel depth of small boats.
The reefs, probably formed from quarried rock, could simply be
dropped into place. The reefs would, in addition to their function
of increasing tidal stream velocity, would serve as a shelter
and breeding ground for fish. However, prediction of the effect
of reefs on tidal stream flow is not simple. There would appear
to be a need for computational fluid dynamical studies of a novel
kind. I would like to suggest that these studies should be funded
at the same time as the resource is being studied.
The importance of increasing tidal stream velocities, if
possible, can hardly be exaggerated. The number of turbines required
is reduced by a significant factor (eight, if the velocity could
be doubled) and this would have a marked effect on capital cost.
20. Suggested Government Support
The potential of tidal stream energy has existed since the
end of the ice age. It is only in the last few years that the
need to make use of it has been understood as the costs of excessive
use of fossil fuel begin to dawn. Fossil fuel is much too cheap;
however, it is politically inexpedient to cause sharp rises in
While fossil fuel is cheap, industry has no incentive to
invest in tidal stream turbines. A way out of this impasse would
be for government to fund design, construction, siting and setting
to work of the largest practicable tidal stream turbine. The costs
of the enterprise should be underwritten but the profit, which
should be generous, should be released when turbine and generator
have met their specifications. It might be advantageous to make
such contracts with several design and construction teams. Competition
concentrates the mind.
Developing non-polluting sources of power is at least as
important as national defence. If even one-tenth of defence funding
were allocated, and rigorously supervised, the problem would be
solved within a few years.
When power and fuel from renewable sources are available
in quantity it will be possible to raise the price of fossil fuels
to levels more commensurate with the cost of using them. This
will not only improve the environment but will conserve valuable
resources which are, at present, being consumed in a prodigal
2 February 2001