This feasibility study examines tidal mills in the UK as a source of renewable energy. The study calculates the power output and economic feasibility of restoring seven existing tidal mills under different tidal conditions. The results show that power outputs range from 7.8KW to 160.9KW, with capacity factors of 14-23%. Economic analysis finds that all mills could generate a profit from feed-in tariffs except the smallest mill. Technological feasibility is highest for larger mills. While tidal mills provide local power at a micro scale, their environmental impacts would require assessment and mitigation.

1. A Feasibility Study into
Tidal Mills as a Source of
Power
Rhys Hobbs 15071588
MSc. Renewable Energy and Resource Management

2. Introduction- UK tidal Resource
Type Location Indicative annual energy [TWh/year] Indicative maximum power [GW]
Tidal stream
England 34 11
Wales 28 9.5
Scotland 32 11
Northern Ireland 1 0.5
Total 95 32
Tidal range: barrage
England 57 27
Wales 23 8
Scotland 16 10
Total 96 45
Tidal range: lagoon
England 14 8
Wales 7 3.5
Scotland 4 2.5
Total 25 14
The U. K’s tidal resource, per region and type of tidal device. Source: The Crown Estate

3. Introduction – Tide Mills
 A tide mill is a simple water mill that
harnesses the power of the rising and
falling tide , A mill pond is created by
forming a dam across an appropriate area,
whether that is a tidal inlet, or a part of a
river estuary.
 When the tide rises, the water enters the
mill pond through a gate and channel
known as a penstock. This gate then closes
when the tide beings to drop, storing a
large amount of water in the mill pond,
gathering potential energy. When the tide
drops to a certain level, the gate is re-
opened and the water is released and
subsequently turns the water wheel.
Diagrams showing how the tide mill work when the tide falls (Minchinton, 1979)

4. Aims and Objectives
The overarching aim for this dissertation project is:
 To complete and evaluate a feasibility study into tidal mills as a source of
renewable energy for the U.K
 Objectives:
 To calculate the power output of the tidal mills at spring, neap and regular
tides
 To analyse the various types of tidal technology and whether they are suitable
for use in tidal mills
 To critically evaluate the potential environmental impacts of the scheme
 To examine the feasibility of the technology of the scheme
 To analyse the potential economic feasibility of the small scale tidal scheme

5. Methodology – Tide data
Various tidal data points. Source: www.willyweather.co.uk

6. Methodology – Tide Mills
Tide Mill Location Current Status
Thorrington Tide Mill Thorrington, Essex Operational
Eling Tide Mill Eling, Hampshire Operational
Three Mills Tide Mill Bromley-by-Bow, London Restored, not operational
Woodbridge Tide Mill Woodbridge, Suffolk Restored, not operational
Tide Mill Newhaven, East Sussex Demolished - Sluice only
Carew Mill Carew, Pembrokeshire Restored, not operational
Pembroke Tide Mill Pembroke, Pembrokeshire Demolished - Mill pond and Sluice only

7. Methodology - Technology
 As all of the mills in the study have
been refurbished and repurposed
or derelict, the turbine needed for
the generation of electricity has to
be chosen, as it will affect the
overall power output of the
turbine.
 As tidal mills work on a similar
level to hydro-electric power
(pumped storage) then there are a
number of available options in
regards to which turbine will be
most applicable for the mills
themselves.
Diagram of a Kaplan turbine. Source: (Charlier, 1982)
Diagram of a Francis turbine source: (Charlier, 1982)

8. Methodology - Calculations
 Change in mill pond over time:
 −𝑉 × 𝑇𝑖𝑚𝑒 + 𝑀𝑎𝑥 𝑡𝑖𝑑𝑎𝑙 𝑟𝑎𝑛𝑔𝑒
 Volumetric flow rate:
 𝑄 = 𝐴𝑉
 Power output:
 P = Ƞ ρ g Q H
Trash Rack Losses
Equation
Head losses calculation

9. Methodology - Calculations
 Kaplan Turbine costs
 CK = 15000 × (Q × H) 0.68 (£)
 Feed in Tariffs
 Export Tariffs
Hydro generating
station with total
installed capacity of
less than 100kW
p/kwh
1 Apr to 30 Jun 2016 7.68
1 Jul to 30 Sep 2016 7.66
1 Oct to 31 Dec 2016 7.65
1 Jan to 31 Mar 2017 7.63
Feed in Tariff rates for normal hydro, source: (Ofgem.gov.uk, 2016)

10. Results - Thorrington
Spring Neap Normal
Total Losses
(m)
0.029818553 0.000319585 0.000381925
SPRING NEAP NORMAL
Total £ for generation £2511.10 £1097.32 £5336.63
Spring Neap Normal
Total £ for Export £1609.59 £703.37 £3420.74
Total Power Output:
111.5KW
Capacity Factor:
19.5%

11. Results - Eling
Total Power Output:
 73.7KW
Capacity Factor:
 21%
Spring Neap Normal
Total Losses 0.015278012 0.000157241 0.077412627
SPRING NEAP NORMAL
Total £ for generation £1513.94 £631.78 £4506.41
Spring Neap Normal
Total £ for Export £828.12 £345.58 £2,464.99

12. Results – Bromley By Bow
Total Power Output:
 48.02KW
Capacity Factor:
 16%
Total Losses Spring Neap Normal
0.001327291 2.23464E-05 2.84E-05
SPRING NEAP NORMAL
Total £ for generation £845.26 £561.18 £2898.56
Spring Neap Normal
Total £ for Export £462.36 £306.97 £1,585.51

13. Results - Woodbridge
Total Power Output:
 7.87KW
Capacity Factor:
 23%
Total Losses Spring Neap Normal
0.000354741 4.61164E-06 6.88E-06
SPRING NEAP NORMAL
Total £ for generation £151.58 £78.56 £477.07
Spring Neap Normal
Total £ for Export £82.91 £42.97 £260.96

14. Results - Newhaven
Total Power Output:
 106.85KW
Capacity Factor:
 21%
Total Losses Spring Neap Normal
0.016131975 0.000175263 0.000273
SPRING NEAP NORMAL
Total £ for generation £2,220.47 £975.54 £6,180.63
Spring Neap Normal
Total £ for Export £1,214.59 £533.62 £3,380.79

15. Results - Carew
Total Power Output:
 60.61KW
Capacity Factor:
 14%
Total Losses Spring Neap Normal
0.027767721 7.5754E-05 0.000253
SPRING NEAP NORMAL
Total £ for generation £1801.04 £201.09 £2735.92
Spring Neap Normal
Total £ for Export £985.16 £110.00 £1,496.54

16. Results - Pembroke
Total Power Output:
 160.97KW
Capacity Factor:
 14%
Total Losses Spring Neap Normal
0.237035131 0.000646538 0.002162
SPRING NEAP NORMAL
Total £ for generation £4,554.98 £586.90 £7,977.68
Spring Neap Normal
Total £ for Export £2,491.56 £321.03 £4,363.77

17. Discussion – Technological Feasibility
 In terms of feasibility, Woodbridge (7KW) would be the least feasible
purely on the basis that it produces the least amount of power.
 For hydro technologies, the capacity factor usually ranges between 20
and 50% over a monthly period.
 Although the tide is regular, the water level in the mill pond is simply
not high enough to generate a substantial amount of power.

18. Discussion – Economic Feasibility
 Without utilising both of these tariffs, the mills simply wouldn’t
generate enough money to be sustainable.
 The Kaplan turbine costs vary greatly per site, the general pattern
was if a site had a large head and fast volumetric flow rate, then the
cost of the turbine went up significantly.

19. Discussion – Economic Feasibility
 Apart from Pembroke and Newhaven, all of the tide mills are fully
restored and have been refitted for different purposes, but the key
features such as the penstock and trash rack are still in place.
 This means that in order for these Mills to be fitted for electricity
generation, they simply need to be refurbished to accommodate the
turbine and generator. This is relatively cheap compared to Pembroke
and Newhaven, which would have to be built rather than re-fitted.

20. Discussion – Environmental impacts
 Before commissioning any renewable energy project, an
environmental impact assessment has to be carried out in accordance
with EU regulations. Assessors evaluate the site for potential impact
areas and draw up a detailed report on their findings that can be used
in tailoring the project to negate as much of these impacts as
possible.
 Some impacts include:
 Potential flooding
 Turbine damage due to fish and debris

21. Assumptions
 The same method of calculation was used for the tidal mills as a
previous method for hydroelectric power plants.
 The turbine efficiency was assumed to stay constant through the four
hours of generation.
 The length, diameter and material of the penstock was kept the same
for all the sites, based on research. As all of the sites fell into a small
range of head sizes, the same length and diameter was used for each
one

22. Limitations
 By presuming all of the penstock lengths are the same, some sites
may have a greater head loss than they should get, as different sizes,
even if by millimetres could make the penstock more efficient.
 Although several of the mills had websites, there was very little data
available in order to get accurate measurements of the mill pond, and
google earth had to be used in order to get area data.
 By averaging the tide ranges that are not influenced by the spring or
neap tides, the normal tide range does not take into account the
regular fluctuations of the tide.

23. Further Study
 Accurate tidal readings for the year can be taken at each mill
location, which means that each high tide and low tide can be
analysed precisely and give coverage for the whole year in terms of
power and money generated.
 The mill ponds can be properly surveyed, whether it is by bathymetry
or simple measuring techniques, to give an accurate reading of the
mill pond level and the mill pond base height above sea level

24. Conclusions
 To summarise these three aspects (technological, economical and
environmental), tidal mills are feasible to a certain extent as a source
of renewable power, however, this power can only be classed as micro
scale, and they are better for providing local communities with power,
rather than generating power for the grid

25. References
 Minchinton, W. (1979). Early Tide Mills: Some Problems. Technology and Culture,
20(4), p.777.
 UK Wave and Tidal Key Resource Areas Project. (2012). 1st ed. [ebook] London:
The Crown Estate. Available at:
https://www.thecrownestate.co.uk/media/5476/uk-wave-and-tidal-key-
resource-areas-project.pdf [Accessed 9 Sep. 2016].
 Charlier, R. (1982). Tidal energy. New York: Van Nostrand Reinhold.
 Tides.willyweather.co.uk. (2016). Tide Times - United Kingdom - WillyWeather.
[online] Available at: http://tides.willyweather.co.uk/ [Accessed 1 Sep. 2016].

26. Any Questions?