i Declaration of originality I certify that this is my own work, and it has ...

Declaration of originality
I certify that this is my own work, and it has not previously been submitted for
any assessed qualification. I certify that the use of material from other
sources has been properly and fully acknowledged in the text. I understand
that the normal consequences of cheating in any element of an examination, if
proven and in the absence of mitigating circumstances, is that the Examiners’
Meeting be directed to fail the candidate in the examination as a whole.
Signed:
……..………………………………………………………………………………
Date:
……………………….……………………………………………………………….
i

Abstract
The current situation and prospects for small wind turbines (

Executive summary
This report examines the current situation and prospects for small wind turbines
(

their turbines, suffered from poor after sales service, and overrate the economics. The
most significant obstacles to installation encountered were planning and connecting to
the grid (neighbours and the local community had comparatively little effect). A
significant proportion of those who responded had also depended on grants.
Installed costs for the turbines are estimated based on data collected, and by £/kW are
found to approximately corroborate with the Clear Skies estimate of £2,500-5,000 per
kW. Economic estimates for building-mounted installations are not significantly
more expensive than ground-based installations for turbines of the same type.
Initial economic modelling is completed for turbines at a school in Glasgow, a house
in Reading, and the RIBA (Royal Institute of British Architects) and Aylesbury Estate
buildings in London. The last three sites all have measured wind speed data which is
why they have been chosen, because NOABL (a wind speed database widely used by
the industry) does not make accurate predictions where the local topography has a
large effect (e.g. in the urban environment). The economic analysis for the school is
for ground-based turbines, for the London buildings building-mounted turbines, and
for the house both kinds. The economics for all of the installations are found to be
poor, apart from the Aylesbury Estate where a payback of 5 years could be achieved
with a building-mounted Proven 6kW if 50% of installation costs are grant-funded
and ROCs are collected. This is due to the high AMWS of 8m/s on the rooftops of
the Estate’s tower blocks. AMWSs in the other measured areas are much lower,
2.8m/s in central Reading, and 3.4m/s on RIBA’s rooftop, and leads to paybacks >20
years. Installations in all the areas are shown to be predominantly sensitive to
changes in wind speed, followed by level of initial investment, (other variables
measured included ROCs, discount rate, and annual maintenance costs).
The research has been carried out with IT Power as part of the EC-funded WINEUR
project. This work focuses on the UK & Ireland, while the WINEUR project is
covering technologies and the state of the market in Europe.
iv

SMALL WIND TURBINES FOR THE URBAN ENVIRONMENT:
STATE OF THE ART, CASE STUDIES, & ECONOMIC ANALYSIS
TABLE OF CONTENTS
Declaration of originality
Abstract
Executive Summary
Table of Contents
List of figures and tables
Glossary of terminology
Acknowledgements
i
ii
iii
v
vii
ix
x
Chapter 1 INTRODUCTION
1.1 Renewable energy & microgeneration targets 1
1.2 Possible benefits of urban µgeneration, and small wind
2
1.3 The WINEUR project
2
1.4 Aims & objectives of this project
3
Chapter 2 METHODOLOGY
2.1 Methodology 4
2.2 Note on references 5
Chapter 3 STATE OF THE ART – UK & IRELAND
3.1 The urban wind regime 6
3.2 HAWT vs. VAWT, lift vs. drag
6
3.3 Building-mounting
8
3.4 Categorising small wind turbines with respect to the urban
environment
9
3.5 State of the art summary
10
3.6 Technical comparisons of similar turbines
14
3.61 Power & efficiency comparisons on the “small HAWTs aimed
at the urban market”
14
3.62 Power & efficiency comparisons on “the larger HAWTs”
16
3.63 The importance of low cut-in wind speeds
18
3.64 Cut-out wind speeds
21
3.65 Weight per swept area – turbine robustness
23
3.66 RPM (Revolutions Per Minute) & TSR (Tip Speed Ratio)
24
Chapter 4 UK INSTALLATIONS
4.1 Limitations to the study 25
4.2 Installations found - results
4.3 The returned questionnaires
4.31 Demographics
25
27
28
4.32 Turbine details 29
4.33 Location type 30
4.34 People’s perspectives of the turbine 31
4.35 Economics & lack of knowledge of turbine operators 34
4.36 Reasons for installation 36
4.37 Obstacles to installation 37
v

4.38 Turbine problems & after sales service 38
4.39 With hindsight, would they install a small wind turbine again? 38
4.4 Analysis of results 39
4.41 Of all the installations found 39
4.42 Of the returned questionnaires 40
Chapter 5 ECONOMICS
5.1 Methodology 43
5.2 Estimated installed costs per kW e for turbines 44
5.3 St. John Bosco School, Renfrewshire
5.4 A traditional house in central Reading, Berkshire
5.5 Large buildings in London – RIBA, and the Aylesbury Estate
5.6 Analysis
Chapter 6 CONCLUSIONS 61
REFERENCES 64
APPENDICES
Appendix A Wind turbine details
Appendix B Catalogue of wind turbines on the market
Appendix C Catalogue of prototype wind turbines
Appendix D Permanent magnet or induction generators?
Appendix E Full list of known installations
Appendix F Blank sample case study questionnaire
Appendix G Raw questionnaire data
Appendix H Additional installation results
Appendix I The variables for economic analysis
Appendix J Approximate installed turbine costs
Appendix K Full installation costs for different turbines at John Bosco
School
Appendix L Important conversations and emails
Appendix M Economic questionnaires
46
50
55
59
vi

List of figures and tables
Figure 1– the HAWT categories and their rotor diameter ...........................................10
Figure 2 – Power vs. wind speed for the “small HAWTs aimed at the urban market”15
Figure 3 – Power per m 2 of swept area vs. wind speed for the “small HAWTs aimed at
the urban market”.........................................................................................................15
Figure 4 – Fraction of the Betz limit attained by the “small HAWTs aimed at the
urban market” vs. wind speed......................................................................................16
Figure 5 – Power vs. wind speed for “the larger HAWTs” .........................................17
Figure 6 – Power per m 2 of swept area vs. wind speed for “the larger HAWTs” .......17
Figure 7 – Fraction of the Betz limit attained by “the larger HAWTs” vs. wind speed
......................................................................................................................................18
Figure 8 – kWh the D400 generates due to wind speeds in the ‘bins’ of 3m/s and 3 &
4m/s at different AMWSs ............................................................................................19
Figure 9 – Percentage of the total annual energy capture of the D400 due to wind
speeds in the ‘bins’ of 3m/s and 3 & 4m/s at different AMWSs .................................20
Figure 10 – kWh the Proven 15kW generates due to wind speeds in the ‘bins’ of 3m/s
and 3 & 4m/s at different AMWSs ..............................................................................20
Figure 11 – Percentage of the total annual energy capture of the Proven 15kW due to
wind speeds in the ‘bins’ of 3m/s and 3 & 4m/s at different AMWSs ........................21
Figure 12 - kWh the Proven 0.6kW and the Swift generate due to wind speeds in the
‘bins’ ≥15m/s at different AMWSs..............................................................................22
Figure 13 – Percentage of the total annual energy capture that the Proven 0.6kW and
the Swift generate due to wind speeds ≥15m/s or ≥20m/s at different AMWSs.........23
Figure 14 – Weight per swept area of the turbines ......................................................24
Figure 15 – Locations of all 92 installed turbines........................................................26
Figure 16 – Turbine models chosen.............................................................................27
Figure 17 – Turbine models chosen.............................................................................29
Figure 18 – Locations of installed turbines..................................................................30
Figure 19– Owner’s overall happiness with their turbine............................................31
Figure 20– Owner’s rating of the visual appearance of their turbine ..........................32
Figure 21 – Neighbours’ and local communities’ perceptions before the installation 33
Figure 22 – Neighbours’ and local communities’ perceptions after the installation ...33
Figure 23 – Owner’s estimates of the turbine’s paybacks ...........................................35
Figure 24 – Reasons listed for installing the turbine ...................................................36
Figure 25 – Owner’s rating of the difficulty in overcoming obstacles ........................37
Figure 26 – Estimated turbine installed costs in £/kW ................................................44
Figure 27 – John Bosco School’s turbine and its location...........................................46
Figure 28 – LPC sensitivity analysis for John Bosco School ......................................48
Figure 29 – Estimated LPCs for different turbines installed at John Bosco School....49
Figure 30 – Map of central Reading ............................................................................51
Figure 31 – LPC sensitivity analysis for the installation of a Swift on a house in
Reading ........................................................................................................................54
Figure 32 – Map of RIBA’s location in London..........................................................55
Figure 33 – Map of Aylesbury Estate’s location in London........................................56
Figure 34 – LPC sensitivity analysis for a roof-mounted Proven 6kW on the
Aylesbury Estate ..........................................................................................................59
vii

Table 1– the DTI’s definition of microgeneration.........................................................1
Table 2 – Advantages & disadvantages of HAWTs, Lift VAWTs, & Drag VAWTs...7
Table 3 – Summary of manufacturers..........................................................................11
Table 4 – Turbines being manufactured for the urban environment ...........................12
Table 5 – Prototypes being 12designed for the urban environment ............................12
Table 6 – Turbines on the market which are suitable for building-mounting 13
Table 7 – Prototypes which should be suitable for building-mounting .......................13
Table 8 – Breakdown of total number of installations.................................................25
Table 9 – Number of known rooftop installations.......................................................27
Table 10 – Locations of installed turbines...................................................................28
Table 11– base case of the school for LPC sensitivity analysis ..................................47
Table 12 – estimated installed costs for turbines at John Bosco School .....................49
Table 13 – Estimated economics of residential turbine installations in Reading ........52
Table 14 – Base case for residential Swift installation in Reading, for LPC sensitivity
analysis.........................................................................................................................53
Table 15 – Economics of roof-mounted turbines on RIBA & the Aylesbury Estate ..57
Table 16 – Base case for roof-mounted Proven 6kW on the Aylesbury Estate, for LPC
sensitivity analysis .......................................................................................................58
viii

Glossary
AMWS Annual Mean Wind Speed
BEAMA British Electrotechnical and Allied Manufacturers’ Association. With
respect to microgeneration, they are interested in how exports could be
metered.
Betz limit Theoretical maximum limit to the amount of energy that can be
extracted from an airflow, for either HAWTs or VAWTs. The limit is
59.3% of the energy in the wind.
CREDIT Centre for Renewable Energy, at Dundalk Institute of Technology
CREST Centre for Renewable Energy Systems Technology, at Loughborough
University
DTI Department of Trade and Industry
EERU Energy and Environment Research Unit, at the Open University in
Milton Keynes
G59 & G83 grid connection standards. When a renewable energy generator
connects to the grid, they must ensure that they meet these standards.
GLA Greater London Authority
HAWT Horizontal Axis Wind Turbine
LPC Levelised Production Cost is the present cost of the energy from e.g. a
turbine given the costs and income it provides over its lifecycle
(normally assumed as a 20 year period).
µgenerator (Microgenerator) DTI’s definition, is: < 50kW e , or < 45kW heat, from
a low carbon source.
NOABL DTI database on estimates of AMWSs throughout Britain, to a 1km
square 10, 25, or 45m above ground-level
ODPM Office of the Deputy Prime Minister
PPS22 Planning Policy Statement 22, issued by the ODPM. Guidance aimed
at encouraging local planning departments to view renewable energy
installations favourably.
Rayleigh Wind speed distribution. Special case of the Weibull where the shape
factor k = 2. The scale factor c depends on the mean wind speed,
therefore the whole shape of the curve can be determined by the mean
wind speed.
ROC Renewable Obligation Certificate
RPM Revolutions Per Minute (of the turbine’s rotor)
SCHRI Scottish Community and Household Renewables Initiative. This is
essentially Clear Skies, but in Scotland. They seem to have more
money to spend on projects than Clear Skies, and their website is more
comprehensive.
SEI Sustainable Energy Installations. A sister company of IT Power that
conducts renewable energy installations.
TSR Tip Speed Ratio
VAWT Vertical Axis Wind Turbine
Weibull Wind speed distribution. Shape of the curve depends on shape factor k,
scale factor c, and the mean wind speed.
ix

Acknowledgements
I would like to thank my supervisor, Tim Cockerill, for his interest and excellent
advice. Special thanks to Katerina Syngellakis, Project Engineer at IT Power, without
whom this project would never have gone ahead, and whose project management
skills and help were invaluable. Many other members of staff at IT Power were
extremely helpful. Particularly Kavita Rai who analyzed some of the data of the
installation questionnaires looking for trends (although most of her work is not
included in this project), and Duncan Brewer whose knowledge and experience in the
subject from an installer’s perspective resulted in frequent conversations and much
help & guidance. Thanks also to Sarah Davidson and Warren Hicks for their
knowledge, and Rolf Oldach for his knowledge of roof-mounting turbines. The
resources that were already available at IT Power – the library of knowledge around
the office and on their computer system collected through their years of work – was
invaluable.
My fellow MSc student from Loughborough University, Steve Carroll, who was
working in parallel with me on the project was also of great helping in broadening my
knowledge of the subject, providing frequent conversations, and solicit responses to
the case study questionnaire.
I would also like to thank the other members of the WINEUR project – primarily for
designing the technical questionnaire which I utilized for obtaining technical data on
the turbines, and also for their research into the wind turbines and state of the market
in other countries around the world, that helped me to gauge the UK’s global position
in this field. They also provided the principal economic questionnaire, which I used
to interview manufacturers, and Steve Carroll and I modified to send to case studies.
x

1. INTRODUCTION
1.1 Renewable energy & microgeneration targets
Britain has a target to source 10% of its electricity from renewables by 2010, and
“aspires” to source 20% by 2020. Although the Energy White Paper assumes this will
mostly be met by large-scale wind turbines, it also believes that microgeneration will
provide an important contribution and is worth pursuing. (DTI, 2003)
Some local planning authorities’ Unitary Development Plans (so far Merton, Croydon,
and North Devon) now demand that a percentage of energy for all major
developments 1 must be sourced from onsite renewables (SolarCentury, 2005a).
Influence from National planning document PPS22 (ODPM, 2004a) and the Greater
London Authority (GLA, 2004) is strongly encouraging other Local Authorities to
follow suit. 2 Small wind generators are already being used to meet these local targets
(Merton 2004, and SolarCentury 2005b).
Table 1– the DTI’s definition of microgeneration
For heat, < 45 kW
For electricity, < 50 kW e
Low net carbon emissions
(Resouce05, 2005)
The DTI also call microgeneration µgeneration. This is convenient, and hereon it is
used in this project.
1 Definition of a major development. With dwellings: >10 or total area > 0.5 hectares. Other uses:
floor space >1,000m 2 , or site > 1 hectare. (Solar Century, 2005a)
2 The Energy Performance of Buildings Directive, when it comes into force, may also have some
impact (ODPM 2004b), but it remains to be seen how much.
1

1.2 Possible benefits of urban µgeneration, and small wind
This research is worthwhile because of the possible benefits of urban µgeneration.
They can be summarised as:
1. Additional untapped source of renewable energy
2. At point of use and thus eliminating transmission losses
3. Potentially leading to strengthening of the grid (Martin Bradley conversation,
24/5/05) and distribution networks (DTI, 2005), reducing the need for
upgrades
4. Raises awareness of sustainability
In addition, compared to the other µgeneration technologies wind is among the most
economic where wind speeds are reasonable (DTI 2005), and will probably have a
higher Energy Payback Ratio (EPR) and emit less CO 2 over its lifecycle (Boyle et al.
2003, Resource05 2005). Depending on where it is sited, it can be highly visible
making it very appropriate for making a green statement or raising awareness. Small
wind can also complement PV because it generates most of its energy in the winter,
while PV generates most of its energy in the summer. (SolarCentury, 2005b)
1.3 The WINEUR project
Despite the relative potential importance of small scale wind generation in urban areas,
there is as yet very little comprehensive information on the subject, covering both
building-integrated and mast-mounted installations. The EC co-funded WINEUR
project (Wind Integration in the Urban Environment) will fill this information gap by
collecting, analysing and disseminating information on the technical, economic,
planning, policy, and sociological aspects of small wind energy for the urban
environment. One of the main aims of the project is to provide comprehensive
information that will encourage the further development of urban wind µgeneration.
More information on the WINEUR project is available at the project website
www.urbanwind.org.
2

1.4 Aims & objectives of this project
This report covers the following work that forms part of the WINEUR project:
Aims
1. Cover the state of the art of turbines being manufactured and designed in the
UK & Ireland
2. Assess the situation with regards to installations, and analyse detailed
experiences of wind turbine owners & operators
3. Analyse the economics
Objectives
1. Technology inventory for the UK & Ireland, containing technical details and
comparing technologies
2. UK installations assessment, estimating the number and kinds of installations,
and analysing some detailed experiences
3. Economic assessment, of the viability of small wind turbines in urban areas
By itself, this work is sufficient to give an insight into the state of urban wind in
Britain today.
It is worth noting that the UK is among the most advanced countries in the world in
this field. Only the Netherlands and Japan are on a comparable level with regards to
developing urban wind turbines and attempting roof-mounted installations.
(WINEUR, 2005)
3

2. METHODOLOGY
2.1 Methodology
To obtain technical details on the British & Irish turbines suitable for the urban
environment:
1. Adapted & utilised a standard technical questionnaire prepared by the
WINEUR partners to interview manufacturers & designers of small wind
turbines (in addition to the questionnaire answers comprehensive notes were
made on any additional comments)
2. Going beyond the requirements of WINEUR, the turbines were then split into
broad categories depending on their intended use (i.e. urban or non urban) and
design (power, rotor diameter, and axis), and then analysed & compared
To summarise the situation with regards to urban installations, and find some detailed
experiences:
1. Researched installations using the internet. Useful websites included: Clear
Skies, SCHRI, Wind & Sun, EcoArc, Community Environmental Networks
(CEN), SEE Stats, BWEA, Action Renewables, and BBC. Ensured
installations identified were urban by locating them on a map.
2. Some analysis of these known urban installations was made – popularity of
types of turbine, who are installing them, percentage which are roof-mounted.
3. Created a standard questionnaire from scratch for distribution to small wind
turbine owners & operators. Covering sociological, technical, and economic
aspects.
4. Input the data received into a spreadsheet, and analysed it with regards to the
sociological, technical, and economic aspects. Kavita Rai of IT Power also
used specialist to make further comparisons according to my suggestions (and
some of her own).
This second task provided some valuable information for the sociological and
economic aspects of the WINEUR project.
4

To analyse the economics:
1. Utilised a standard economic questionnaire prepared by the WINEUR partners
to interview turbine manufacturers.
2. Modified the questionnaire, and emailed it to those who had returned
installation questionnaires and who had agreed to answer further economic
questions.
3. Utilised economic data from the returned case study questionnaires, & other
sources
4. Obtained a spreadsheet of 151 turbine installations (economic breakdown,
AMWS, and generation estimates) made through the Clear Skies program.
5. Accessed economic information from the case studies available on the SCHRI
and Clear Skies websites, and the other studies available.
6. Obtained AMWS data
7. Utilised the turbine power curves obtained from the turbine manufacturers,
with AMWS estimates & a Rayleigh distribution to produce generation
estimates.
Further details on the methodology are in Chapter 5 below.
2.2 Note on References
As much of the research completed was first-hand, many of the references are
discussions and emails with people. These references are contained in Appendix L in
the back of the project, and they are referred to with the name of the person
communicated with, the way the communication was made (i.e. conversation or
email), and the date. In Appendix L they are ordered by date.
5

3 STATE OF THE ART – UK & IRELAND
3.1 The urban wind regime
Two things particularly characterise the urban wind regime – lower AMWSs (Annual
Mean Wind Speeds) compared to rural areas, and more turbulent flow. The lower
AMWSs are caused by the “rough uneven ground” (i.e. a higher roughness length z 0 )
which causes wind to increase with height more slowly. The turbulent flow is a result
of the wind interacting with the buildings.
Despite the advantages in bringing local wind generation to cities, the low AMWSs
and turbulent flow have discouraged many people who may otherwise have been
interested, as wind economics are totally dependent on the available resource. (Gipe,
2004)
Turbulent flow presents challenges in two ways – rapidly changing wind direction,
and buffeting the turbine blades. The options are to find a machine that copes well
with turbulence, or to find the least turbulent areas of the urban environment. Of the
latter, building-tops could show a great deal of promise, partly because the wind flow
there could be substantially greater as it gets concentrated by passing around the
building. Other less turbulent areas are open areas on the ground such as school
playing fields or parks.
3.2 HAWT vs. VAWT, and lift vs. drag
There is some debate about which of the different kinds of turbine are most suitable
for the urban environment, which would be best for building-mounting, and even
whether building-mounting is a good idea.
The advantages and disadvantages of the main different designs of machine are
summarised in table 2 below.
6

Table 2 – Advantages & disadvantages of HAWTs, Lift VAWTs, & Drag
VAWTs
HAWTs Lift VAWTs Drag VAWTs
Advantages 1. Efficient
2. Proven product
3. Widely used
4. Most economic
5. Many products
available
1. Quite efficient
2. Wind direction
immaterial
3. Less sensitive to
turbulence than a
HAWT
4. Create fewer
vibrations
Disadvantages 1. Does not cope well 1. Not yet proven
with frequently 2. More sensitive to
changing wind turbulence than
direction
drag VAWT
2. Does not cope well
with buffeting
(Randall 2003, Timmers 2001, and Clear Skies 2003)
1. Proven product
(globally)
2. Silent
3. Reliable& robust
4. Wind direction
immaterial
5. Can benefit from
turbulent flows
6. Create fewer
vibrations
1. Not efficient
2. Comparatively
uneconomic
An unmodified HAWT will work well where the air flow is less turbulent, on top of
high buildings or near open spaces, but in more turbulent areas HAWTs would need
to be made robustly in order to cope with blade-buffeting. Detrimentally, this will
increase the turbine’s weight and cost (John Balson conversation, 18/5/05). In fact,
many of the HAWTs aimed at the urban market are heavy with respect to surface area,
probably for this reason. However this would not solve the issue of them being
unable to orient themselves quickly enough to catch all the energy when the wind
direction is prone to change frequently.
7

Other, less certain issues are that:
1. Lift VAWTs may not be able to cope with strong turbulence either, because
they also rely on lift and so their blades would frequently stall (Ken England
conversation, 19/5/05)
2. VAWTs should be easier to maintain, as the generator is below the rotor,
normally on the ground. (Timmers 2001 & Clear Skies 2003)
3.3 Building-mounting
Some respected people within the small wind turbine industry such as Paul Gipe and
Mick Sagrillo are against rooftop mounting. They are concerned over vibrations
being transmitted to the structure, and the turbulence caused by the roof. (Gipe, 2003)
In addition, Larry Staudt (formerly Engineering Manager of Enertech) found that it
was very difficult to get a rotor diameter on a roof big enough to get a significant
amount of power. (Larry Staudt conversation, 19/5/05)
Indeed, structural integrity due to vibrations and dynamic loads is a significant current
concern in building-mounting turbines. Hiring a structural engineer to assess the
suitability of the buildings is a major cost, as is altering the structure (e.g. by adding
steel frames). (Rolf Oldach conversation 16/6/05, Clear Skies 2003) In addition,
Gipe, Sagrillo, & Staudt’s experiences are predominantly with HAWTs, and VAWTs
create less vibrations, exert smaller dynamic loads on the building, and can cope
better with turbulence. (However, they are also currently less economic.) (Clear
Skies, 2003)
Advantages of building-mounting are:
• potentially much higher wind speeds (depending on relative height
of the building compared to surrounding buildings – see Chapter 5
below)
• less turbulence
8

3.4 Categorising small wind turbines with respect to the urban environment
For the purposes of this report small wind turbines are placed into five principal
categories:
• micro HAWTs
• small HAWTs not aimed at the urban market
• small HAWTs aimed at the urban market
• larger HAWTs
• VAWTs
The definitions of these categories are as following:
Micro HAWTs – very small HAWTs designed and marketed for remote locations or
boats, which in normal conditions would produce too little power to noticeably reduce
an ordinary domestic (or other) electricity bill. 3 In addition, G83-certified inverters
that could grid-connect the tiny amounts of power they produce cost more than the
turbines in August 2005. (Peter Anderson conversation, 9/8/05)
Small HAWTs not aimed at the urban market – HAWTs that would produce a
significant amount of power, but are still aimed at remote locations.
Small HAWTs aimed at the urban market – HAWTs that are designed & marketed for
the urban market and should produce enough power to noticeably reduce a normal
domestic (or other) electricity bill.
Larger HAWTs – the larger HAWTs with a rotor diameter >2m, aimed at either the
urban or rural markets.
VAWTs – currently, the VAWTs can all be conveniently grouped together.
3 Gipe defines micro turbines as being those with a rotor diameter of under 1.25m (Gipe, 2004), which
correlates with this definition.
9

Figure 1– the HAWT categories and their rotor diameter
12
1 = Micro HAWTs
10
2 = Small HAWTs not
aimed at the urban
market
3 = Small HAWTs that
are aimed at the urban
market
4 = Larger HAWTs
Rotor diameter, m
8
6
4
2
0
1 2 3 4
Turbine type
Figure 1 above compares the categories of the HAWTs, with the rotor diameters of
the turbines, to see if there is any correlation. Category 3 overlaps slightly with
categories 1 and 2 because it is primarily defined by the fact that these turbines are
aimed at the urban market, and not by their rotor diameter.
3.5 State of the art summary
There are 11 companies (2 of which are Irish) manufacturing 19 small wind turbines
(all HAWTs). There are 12 organisations (1 of which is Irish) designing and
developing small wind turbines (5 HAWTs & 7 VAWTs). Of these 12, 4 are also
manufacturers, so 19 organisations in total are either manufacturing or designing 31
small wind turbines, all of which could theoretically be placed in the urban
environment.
The proven products that generate a substantial amount of energy and are available
now for the built environment are the “larger HAWTs” made by Proven, Iskra, and
Gazelle. These products are almost always ground-based, with the exception of
Proven who have recently started building-mounting their turbines. Other proven
products that could be used in the urban environment are the “micro HAWTs”,
although they generate so little power their applications would be limited.
Products which are just emerging (or have emerged recently) onto the market which
are specifically intended to be building-mounted on domestic properties (and other
10

uildings) are the “small HAWTs aimed at the urban market” made by Eclectic
Energy, Renewable Devices, and Windsave. (There is one other recent product in this
category – Surface Power’s turbine – but it can’t be building-mounted.)
There are no VAWTs currently on the market, 4 but many VAWTs designed for the
built environment (and that should be suitable for building-mounting) are prototypes
currently being tested, and should be available in 2006/2007.
Table 3 below summarises the different companies, the categories of turbines they
manufacture, and how long they have been manufacturing them for.
Table 3 – Summary of manufacturers
Turbine type Company Years manufacturing,
in 2005
Micro HAWTs
Small HAWTs not aimed
at the urban market
Small HAWTs that are
aimed at the urban market
Larger HAWTs
Marlec
LVM
Ampair
Marlec
Atlantic Power Master (Irish)
Eclectic Energy
Surface Power Technology
(Irish)
Windsave
Renewable Devices
Iskra
Proven
Gazelle
> 25
≥ 25
≥ 25
> 25
2
≥ 3 (other turbines) 5
This year
This year
This year
This year
14
7
(George Durrant email 8/7/05, Marlec 2005, LVM 2005, Atlantic Power Master 2005,
Eclectic Energy 2005, Surface Power Technology 2005, Windsave 2005, Renewable
Devices 2005, Iskra 2005, Proven 2005, MKW 2005)
4 Although Ampair used to make a Savonius VAWT for boats called the “Dolphin”, it was withdrawn
due to its extremely low efficiency and power rating. (George Durrant conversation, 16/5/05)
5 Meaning that Eclectic Energy have been making a product which is both wind & water turbine for use
on boats for at least 3 years. However, their new urban wind turbine product is new in 2005.
11

Tables 4 & 5 below summarise the turbines currently being directed at the urban
environment. In table 5, some turbines may be unfairly excluded, due to a lack of
knowledge.
Table 4 – Turbines being
manufactured for the urban
environment
Model & Rated
Manufacturer power,
kW
D400 (Eclectic 0.4
Energy)
Surface Power 0.46
Technologies
Windsave 1
Swift (Renewable 1.5
Devices)
Proven WT600 0.6
Proven WT2500 2.5
Iskra
5
Proven WT6000 6
Proven WT15000 15
Gazelle
20
Table 5 – Prototypes being
designed for the urban
environment
Model &
Rated
designer/developer power,
kW
CREDIT
Rugged Renewables
Eurowind
FreeGEN
Posh Power
Swift, smaller version
(Renewable Devices)
XCO2
Wind Dam
1.5
0.4
Many (1.3
to 30)
Unknown
~2-2.5
Unknown
6
2 (also in
stackable
modular
design)
(Resource05 2005, (Larry Staudt conversation 19/5/05,
John Quinn email 21/5/05, Ken England conversation 19/5/05,
Renewable Devices 2005, Eurowind 2005, Posh Power 2005,
Iskra 2005, MKW 2005) Richard Cochrane conversation 11/7/05,
Julie Trevithick conversation 16/5/05)
(Although some turbines are being manufactured for the urban environment and
others are not, it is possible that any of them can be found in the urban environment
somewhere.)
From table 4 it can be seen that the three most experienced manufacturers of small
turbines in Britain & Ireland – Marlec, LVM, & Ampair – presently show no interest
in the urban market. This is due to poor wind conditions, and the tiny amounts of
power their products produce. (Graham Hill conversation 13/5/05, George Durrant
conversation 16/5/05, & Stuart James conversation 18/5/05)
12

All the turbines in table 4, and the CREDIT & smaller Swift turbines in table 5 are
HAWTs, which should therefore be designed in a robust manner. All the other
turbines in table 5 are VAWTs.
Of the turbines being made for the urban environment, tables 6 and 7 list those aimed
at building-mounting.
0.4
Table 6 – Turbines on the market
which are suitable for buildingmounting
Model
& Rated
Manufacturer power,
kW
D400 (Eclectic
Proven WT15000 ?? 7 15
Energy)
Windsave
1
Swift (Renewable 1.5
Devices)
Proven WT600 ?? 6 0.6
Proven WT2500 2.5
Proven WT6000 6
Table 7 – Prototypes which
should be suitable for
building-mounting
Model &
Rated
designer/developer power,
kW
Rugged Renewables
Eurowind
Swift, smaller version
(Renewable Devices)
XCO2
Wind Dam
0.4
Many (1.3
to 30)
Unknown
6
2 (also in
stackable
modular
design)
(Resource05 2005, (Ken England conversation 19/5/05,
Renewable Devices 2005) Richard Cochrane conversation 11/7/05,
Julie Trevithick conversation 16/5/05,
Eurowind 2005)
As can be seen from table 6, Surface Power Technologies are absent due to their
concern about vibrations (Jenny email, 11/7/05). Iskra are absent as although they are
interested they believe they would need to design a new turbine, and they are not in
table 7 as it seems this has not begun yet (John Balson conversation, 3/6/05).
Gazelle’s intentions are not certain, but their turbine is probably too big.
In table 7, CREDIT are absent due to their concerns over generating enough energy
and vibrations (Larry Staudt conversation, 19/5/05), while FreeGEN and Posh Power
have been removed as it is not clear if they are intending for their turbines to be
6 Although there are no known examples involving the Proven 0.6kW, it probably could be as the
larger 2.5 & 6kW Provens are being building-mounted.
7 Proven haven’t excluded the possibility of building-mounting their 15kW turbine, but it has not been
done yet, and it has not been possible to confirm that any installations will go ahead.
13

uilding-mounted. Apart from the smaller Swift, all of the turbines in table 7 are
VAWTs.
For individual descriptions of the turbines see Appendix A.
For pictures and technical details of the turbines, please see the catalogues –
Appendices B and C.
3.6 Technical comparisons of similar turbines
This section will focus on the turbines being aimed at the urban market - the “small
HAWTs being aimed at the urban market”, and the “larger HAWTs”. The machines
that are being designed and developed will not be analysed, as their technical
specifications (where available) will probably change.
As mentioned at the beginning of Appendices B & C, there is a need for a small wind
turbine test centre, that will test and independently verify the technical data supplied
by manufacturers. This is particularly the case with data such as power curves.
3.61 Power & efficiency comparisons for the “small HAWTs aimed at the urban
market”
Power curve data for the Windsave is still classified in August 2005, so it can’t be
compared.
14

Figure 2 – Power vs. wind speed for the “small HAWTs aimed at the urban
market”
1600
D400
1400 SPT
Sw ift
1200
Power (W)
1000
800
600
400
200
0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Wind speed (m/s)
Given that the Swift is rated at 1.5kW, while Surface Power’s turbine is rated at
0.46kW and Eclecitc’s D400 at 0.4kW, it is not surprising that in figure 2 the Swift is
shown to produce far more energy than the other two turbines at all wind speeds.
Power per m2 of swept area (W/m2)
Figure 3 – Power per m 2 of swept area vs. wind speed for the “small HAWTs
aimed at the urban market”
600
D400
SPT
500 Sw ift
400
300
200
100
0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Wind speed (m/s)
15

It is much more interesting to compare the products by power per m 2 of swept area as
in figure 3. Surface Power’s turbine cuts-in at a lower wind speed, but the turbines
are broadly similar until 7 and 8 m/s, when the Swift is shown to produce the most
power/m 2 , followed by the D400, and lastly by Surface Power’s.
Figure 4 – Fraction of the Betz limit attained by the “small HAWTs aimed at the
urban market” vs. wind speed
1.8
D400
Fraction of Betz limit attained
1.6 SPT
Sw ift
1.4
1.2
1
0.8
0.6
0.4
0.2
0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Wind speed (m/s)
Figure 4 shows how all three turbines apparently break the Betz limit at 3m/s, but the
Swift is notably for extravagantly breaking the Betz limit at 4 and 5m/s. For many of
the other wind speeds it is also extraordinarily efficient, while this is also the case for
the D400 at 6m/s and below.
The Swift has a ring around it, which could partially concentrate the airflow (Larry
Staudt conversation, 19/5/05) or reduce blade tip losses – but as it is only a few inches
wide (see picture in Appendix B) it is more likely that the power curve supplied is
erroneous.
3.62 Power & efficiency comparisons on “the larger HAWTs”
It should be noted that the power curve data for the Gazelle is based on very old data,
and derived theoretically. (Garry Jenkins email, 12/7/05) Therefore it may not
represent the machines actual performance in the field very well.
16

Power (W)
25000
20000
15000
10000
Figure 5 – Power vs. wind speed for “the larger HAWTs”
Proven 0.6kW
Proven 2.5kW
Iskra 5kW
Proven 6kW
Proven 15kW
Gazelle 20kW
5000
0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Wind speed (m/s)
In figure 5 above, it can be seen that the turbines generate quite different amounts of
power. The most comparable machines are the Iskra 5kW and the Proven 6kW.
Power per swept area (W/m2)
Figure 6 – Power per m 2 of swept area vs. wind speed for “the larger HAWTs”
350
300
250
200
150
100
50
Proven 0.6kW
Proven 2.5kW
Iskra 5kW
Proven 6kW
Proven 15kW
Gazelle 20kW
0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Wind speed (m/s)
In figure 6 above, the Proven 0.6kW stands out for producing the least power/m 2 , and
the Gazelle the second least amount, for wind speeds ≥5m/s. It is difficult to
differentiate the other four turbines, except ≥13m/s where the Proven 2.5kW is
sharply ahead.
17

Fraction of Betz limit attained
Figure 7 – Fraction of the Betz limit attained by “the larger HAWTs” vs. wind
speed
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
Proven 0.6kW
Proven 2.5kW
Iskra 5kW
Proven 6kW
Proven 15kW
Gazelle 20kW
0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Wind speed (m/s)
As might be expected from figure 6, in figure 7 the Proven 0.6kW is predominantly
the least efficient, followed by the Gazelle. This is the case except where wind speeds
are ≤ 4m/s, where the Proven 0.6kW is more efficient than the Gazelle. All the other
turbines are broadly similar. It is interesting to compare this figure with figure 4 for
the “small HAWTs being aimed at the urban market” – none of these turbines break
the Betz limit, or have such extraordinary efficiencies for such wide bands of wind
speed. This indicates again that the power curves for the smaller HAWTs could be
erroneous, especially for the Swift.
3.63 The importance of low cut-in wind speeds
Figures 8, 9, 10, and 11 below demonstrate the importance of a low cut-in wind speed
at different AMWSs, for two machines – Eclectic’s D400 and the Proven 15kW.
These machines have been chosen because they are of completely different sizes. The
D400 cuts-in at ~2m/s, the Proven 15kW at 2.5m/s, and they first generate measurable
amounts of energy at 3m/s.
A Rayleigh distribution assigns probabilities that the wind will have different wind
speeds given the AMWS. It splits the range of wind speeds into different wind speed
18

‘bins’, of 1, 2, 3, etc. m/s. These probabilities can be multiplied by the number of
hours in a year to assess the number of hours in a year that the wind speed will blow
at that wind speed, given the AMWS. These figures can then be multiplied by a
turbine’s power curve, to give an estimate for a turbine’s annual energy generation.
Figures 8 and 10 compare the energy that the turbines generate due to wind speeds in
the ‘bins’ of 3 and 3 & 4 m/s, while figures 9 and 11 show the percentage that wind
speeds in these ‘bins’ contribute to the total annual energy capture. So these graphs
show how much energy these turbines would lose if they cut-in at higher wind speeds.
Figures 8 and 10 correlate approximately with money lost (approximately due to
complications with ROCs, see Chapter 5, but as a rough method use £0.06/kWh).
Figures 9 and 11 show the percentage of total annual energy capture that would be
lost.
For the D400
Figure 8 – kWh the D400 generates due to wind speeds in the ‘bins’ of 3m/s and
3 & 4m/s at different AMWSs
60
At 3 m/s
Energy generated per year, kWh
50
At 3 & 4 m/s
40
30
20
10
0
0 1 2 3 4 5 6 7 8 9 10
AMWS, m/s
19

Figure 9 – Percentage of the total annual energy capture of the D400 due to wind
speeds in the ‘bins’ of 3m/s and 3 & 4m/s at different AMWSs
Percentage of annual energy generation, %
100
90
80
70
60
50
40
30
20
10
0
At 3 m/s
At 3 & 4 m/s
0 1 2 3 4 5 6 7 8 9 10
AMWS, m/s
Proven 15kW
Figure 10 – kWh the Proven 15kW generates due to wind speeds in the ‘bins’ of
3m/s and 3 & 4m/s at different AMWSs
Energy generated per year, kWh
3000
At 3 m/s
2500
At 3 & 4 m/s
2000
1500
1000
500
0
0 1 2 3 4 5 6 7 8 9 10
AMWS, m/s
20

Percentage of annual energy generation, %
Figure 11 – Percentage of the total annual energy capture of the Proven 15kW
due to wind speeds in the ‘bins’ of 3m/s and 3 & 4m/s at different AMWSs
100
90
80
70
60
50
40
30
20
10
0
0 1 2 3 4 5 6 7 8 9 10
AMWS, m/s
At 3 m/s
At 3 & 4 m/s
In summary, from figures 8-11 above, a low cut-in wind speed would make a
noticeable difference to the annual energy capture for AMWSs ≤ 4m/s, and a crucial
difference with AMWSs ≤ 2m/s. There may be many settings in the urban
environment with such small AMWSs (see Chapter 5).
Also, as turbines with induction generators require a gearbox, which results in a
higher cut-in wind speed (see Appendices A & D), they should be avoided where
AMWSs are very low.
However, there is a question of whether the Weibull distribution is an accurate
representation of wind regimes in the urban environment. And it may not be,
according to Tim Cockerill of Reading University.
3.64 Cut-out wind speeds
None of these wind turbines have a cut-out wind speed, apart from the Windsave
which cuts-out at ~15m/s, and the Gazelle which cuts-out at 20m/s.
It is possible to theoretically compare a turbine to what it’s energy capture might be
like if it did not cut-out – by taking the power curves of wind turbines which don’t
21

cut-out, and seeing how much of the annual energy capture at different AMWSs is
generated by wind speeds at and over those cut-out wind speeds.
Figure 12 below tries to estimate how many kWh the Windsave 1kW is losing by
cutting-out at 15m/s, by using the power curves of its nearest equivalents in terms of
rated power – the Proven 0.6kW and the Swift 1.5kW. (Recall that Windsave’s
power curve is not currently available.) The amount of energy that the Windsave
theoretically loses should lie somewhere between the curves for the two turbines.
Figure 13 below tries to estimate what percentage of the annual energy capture these
turbines are losing. The Swift & Proven 0.6kW >15m/s curves should be useful to
make estimates for the Windsave. The Gazelle is more difficult given that it cuts-out
at 20m/s, and only one power curve is available which extends for wind speeds
beyond this – the Swift’s. Therefore, the Swift >20m/s curve is used to make an
estimate for the Gazelle.
The graphs show that a cut-out wind speed of 15m/s only makes a significant
difference to the annual energy generated at AMWSs ≥7m/s, while a cut-out of 20m/s
only makes a difference where AMWSs ≥9m/s.
Figure 12 - kWh the Proven 0.6kW and the Swift generate due to wind speeds in
the ‘bins’ ≥15m/s at different AMWSs
Energy that would be lost annually, kWh
2500
Swift
Proven 0.6kW
2000
1500
1000
500
0
0 1 2 3 4 5 6 7 8 9 10
AMWS, m/s
22

Figure 13 – Percentage of the total annual energy capture that the Proven 0.6kW
and the Swift generate due to wind speeds ≥15m/s or ≥20m/s at different AMWSs
Percentage of annual energy capture that would be
lost, %
35
30
25
20
15
10
5
0
Swift, 15m/s & greater
Proven 0.6kW, 15m/s & greater
Swift, 20m/s & greater
0 1 2 3 4 5 6 7 8 9 10
AMWS, m/s
3.65 Weight per swept area – turbine robustness
This is a way of estimating a turbine’s robustness. Sagrillo says that engineers design
turbines for survival wind speeds on paper, but rarely test the machines at these
speeds. Besides, a wind turbine is more likely to be destroyed by turbulence than
survival rated wind speeds. Therefore, he recommends that one divides the weight of
the full rotor/nacelle assembly, with the swept area. Lightweight turbines can’t
handle sites with strong winds or turbulence. Heavyweight turbines should last longer,
but are more expensive. (Sagrillo, 2002)
His approximate rule is:
>10 kg / m 2 = heavyweight
5-10 kg / m 2 = medium weight

Weight/swept area figures for all the HAWTs are in Appendices B & C, and none of
the machines “lightweight”, and only two are “medium weight” – Surface Power
Technologies’ turbine and Windsave’s. Therefore they may not cope as well at a
turbulent or very windy site as the rest.
Figure 14 below compares the weight per swept area for the turbines being
manufactured which are aimed at the urban environment.
25.00
Figure 14 – Weight per swept area of the turbines
Weight per swept area, kg/m2
20.00
15.00
10.00
5.00
0.00
D400
Surface Power
Windsave
Swift
Proven 0.6kW
Proven 2.5kW
Iskra
Proven 6kW
Proven 15kW
Gazelle
3.66 RPM (Revolutions Per Minute) & TSR (Tip Speed Ratio)
Although a high RPM/TSR makes a turbine noisier, and more prone to wear & tear,
(Sagrillo 2002), there is only RPM data for a few turbines – not enough to make
comparisons with.
24

4. UK INSTALLATIONS
For this section as many examples of small & micro urban wind turbine installations
in the UK were found as possible. The research was mainly conducted on the internet.
4.1 Limitations to the study
There can only be an approximate relationship between the frequency with which
installations have been detected on the internet, and their actual occurrence in the field.
Some organisations are more likely than others to highlight that they have wind
turbines on the internet e.g. schools & environmental centres, while individual
householders are unlikely to do this. So there is a bias towards some kinds of
installations, and against others such as domestic installations and turbines aimed at
that market like: the D400, Surface Power’s, and the Windsave. The extent of the
effect of these biases on the present work is unknown.
4.2 Installations found – Results
Table 8 – Breakdown of total number of installations
0.5kW &

Case studies have been split among urban and semi-urban, which were loosely
defined as follows:
• Urban – where a turbine appears to be in or within 1 km of a densely
populated area (town or city).
• Semi-urban – where a turbine appears to be in or within 500m of a less
populated area (e.g. tightly-knit village, but not a loose scattering of houses).
Of the 92 installations, 71 are urban (77%), and 21 semi-urban (23%).
Figure 15 below shows that 31 of the installations are schools & colleges (34%), and
21 are environmental centres of some type (23%).
Number of installations
35
30
25
20
15
10
5
0
Figure 15 – Locations of all 92 installed turbines
Government research lab
Housing Association properties
Universities
Community centres (non enviro)
Local Authorities
Individual domestic properties
Where installed
Private companies
Environmental centres
Schools & Colleges
Figure 16 below shows all the kinds of wind turbines that have been chosen to be
installed. Where more than one model of turbine was chosen at a site, this is
represented. But if more than one turbine of a model was installed at a site, this is not
represented – and counts as one. The idea of the graph is to gauge the popularity of
turbines among people choosing them. As most of the installations are of one turbine,
it would correlate quite well with a graph of the total number of turbines. The most
popular turbine is the Proven 6kW, followed by the Proven 2.5kW.
26

Two wind turbines are notably absent – the Proven 0.6kW, and Surface Power
Technologies.
No. of times chosen
18
16
14
12
10
8
6
4
2
0
Aerodyn
Wind Dam
Lagerwey 80kW
Figure 16 – Turbine models chosen
Wind Harvester 60kW
Wind Harvester 45kW
Eoltec Wind Runner
Ropatec
Windside
Ampair
Eclectic's D400
Jacobs 29-20
Type of turbine chosen
Proven 15kW
Iskra
Windsave
Gazelle
Proven unknown
Marlec
Swift
Proven 2.5kW
Unknown
Proven 6kW
Table 9 shows that rooftop installations represent 27% of the 92 installations. (22 of
them are urban.)
Table 9 – Number of known rooftop installations
Built Planned Total
19 6 25
4.3 The returned questionnaires
Most of the built installations above were contacted, and asked to complete a case
study questionnaire. An example case study questionnaire is in Appendix F. 19
responses were received out of a possible 71, which is a response rate of 27%. The
raw data of the questionnaires is in Appendix G.
27

There are some limitations to the responses received. The accuracy of the answers
can only be as good as the knowledge of the person responding. Some of the
responses were obviously inaccurate, e.g. with payback times, and generation
estimates. Where identified, inaccuracies have been taken account of.
There are only a limited number of conclusions that can be drawn with 19 responses.
With more responses, perhaps more trends would be apparent. Kavita Rai’s work
consisted of cross-tabulating many results. A selection of these are shown in the
section below and Appendix H, however the majority of them did not show any
correlation and due to the size of her work it has not been included as part of this
report.
4.31 Demographics
Turbine locations
Table 10 – Locations of installed turbines
Frequency Percent
School 5 26.3
College 1 5.3
Environment centre 4 21.05
Local Authority 1 5.26
Environment centre and University 1 5.26
Environment centre and Local Authority 2 10.53
School and Local Authority 1 5.26
Other 4 21.05
Total 19 100
© Kavita Rai, IT Power, 2005
As would be expected, the case studies are dominated by educational establishments
(42%), and environment centres (37%). Local authorities own 4 of the sites above
(21%). The remaining 4 (“other”), are: a housing association, a charitable
organisation, and 2 businesses.
28

Environmental consciousness
One person wasn’t able to reply on behalf of their organisation, but of the rest 13
thought their organisation was “very environmentally conscious” (72%) and 5 thought
it was “fairly environmentally conscious” (28%). An option nobody selected was
“indifferent to the environment”.
4.32 Turbine details
Wind turbines chosen
Figure 17 below broadly correlates with figure 16 above. The most popular turbines
are still the Proven 6kW & 2.5kW.
7
Figure 17 – Turbine models chosen
6
No. of sites at which chosen
5
4
3
2
1
0
Ropatec
Jacobs 29-20
Lagerwey 80kW
Proven 15kW
Marlec 910F
Gazelle
Proven 2.5kW
Proven 6kW
Turbine choice
Number of installations
Of the 19 sites, 15 had only one turbine (79%), two had two, one had three, and one
had four.
29

Ground or roof-mounted, and open space
17 of the responses (89%) were from ground-based turbines, but Heeley City Farm
has a wall-mounted Marlec 910F (as well as a ground-based Proven), and Bradford
West City Community Housing Trust has at least 2 Ropatecs on the roof of a
residential tower block (see Clear Skies 2003).
4.33 Location type
5
Figure 18 – Locations of installed turbines
4
Frequency
3
2
1
0
Dense inner-city
Typical town/city residential area
Industrial development
Commercial development
Small town
Suburban
Village
Country park
Type of area
6 of the installations (32%) are in a village/country park, and can be considered as
“semi-urban”.
30

4.34 People’s perceptions of the turbine
Owner satisfaction
Frequency
10
9
8
7
6
5
4
3
2
1
0
Figure 19– Owner’s overall happiness with their turbine
Very happy Happy Ambivalent "Awaiting
results"
Overall happiness with turbine
Unhappy
Very
unhappy
One person was not able to answer the question above on behalf of their organisation.
This result is a good sign for the small wind industry. 14 people (78%) are “happy”
or “very happy” with their turbine.
The people who were ambivalent, “awaiting results”, and very unhappy, had all had
problems with their turbines (the latter have had severe and ongoing problems). The
ambivalent owns a Proven 6kW, “awaiting results” a Proven 15kW, and the very
unhappy people own a Gazelle and Jacobs turbines.
The very happy people own a Gazelle, Lagerwey, Proven 6kW, and two of them own
Proven 2.5kW’s. Three of them had also had problems with their turbines, although
only two of the happy people had had turbine problems.
31

Owner’s feeling of visual appearance of turbine
One person felt unable to answer this question on behalf of their organisation.
Frequency opinion expressed
14
12
10
8
6
4
2
Figure 20– Owner’s rating of the visual appearance of their turbine
0
Beautiful Pretty Okay Quite ugly Very ugly
Owner's rating of turbine's visual appearance
12 people (67%) felt indifferent about their turbine’s visual appearance, 5 were
positive (28%), and only one was negative.
A Gazelle, Proven 6kW & Proven 2.5kW were all rated as “beautiful”, while the
Jacobs and Marlec were rated as “pretty”. The Proven 15kW was described as “quite
ugly”. Of course, these opinions are highly subjective.
Safety
Out of the 19, 6 rated their turbine as “very safe” (32%), 12 rated it as “safe” (63%),
and the last rated his 5 year-old Gazelle as “about acceptable”.
Owner’s perception of the turbine’s noise level
With the limited data there is very little correlation between the turbine type or
location as shown in Appendix H.
32

Change in neighbours’ and local communities’ perceptions
Opinions of the neighbours and local communities overwhelmingly veered towards
the positive after the installation compared with before, only a few stayed the same,
and none became negative.
Two people were not able to answer these questions, and one simply said that for both
groups “opinion varied” before & after.
Figure 21 – Neighbours’ and local communities’ perceptions before the
installation
7
Neighbours
6 Local community
Frequency expressed
5
4
3
2
1
0
Very negative Negative Indifferent Positive Very positive
Their opinion
Frequency expressed
8
7
6
5
4
3
2
1
Figure 22 – Neighbours’ and local communities’ perceptions after the
installation
Neighbours
Local community
0
Very negative Negative Indifferent Positive Very positive
Their opinion
33

4.35 Economics & lack of knowledge of turbine operators
Grants & loans
Two people were unable to answer this question.
4 organisations (24%) did not have any financial help at all (a school, a business, and
two environmental centres). Only one took out a loan (a business).
Of the 13 which had received grants, 8 (62%) mentioned Clear Skies / SCHRI, 4
mentioned an electricity supplier’s grant stream (31%), 2 their local support team for
Community Renewables Initiative (15%). Other funding sources included: European
Commission; Department of Enterprise, Trade, and Investment (DETI); and
Buckinghamshire County Council. 2 people who had received grants neglected to say
from where. 5 (38%) received grants from more than one source.
Out of the 13 organisations which had received financial support, 8 (62%) said they
would not have been able to proceed without it, and 5 (38%) were not sure. Not a
single one said they would have proceeded anyway.
ROCs
Two people were unable to answer this question.
Only 5 organisations are collecting ROCs (29%), 2 of which found the paperwork
difficult, one had the paperwork completed by their local renewable energy agency,
one did not know, and one disagreed that the paperwork was difficult.
2 people are in the process of completing the ROC paperwork, one of which is finding
it difficult.
10 are not collecting ROCs, none of which said anything about the paperwork.
Generation estimates
One other interesting fact is the lack of knowledge many people have regarding their
small turbines. Of the 14 that were in a position to know how many kWh their turbine
produced, 5 did not know, and at least 2 seemed far too low and 1 far too high. This
is >50% of respondents that did not know how much energy their turbine generates.
34

Therefore many people did not know if this was the same, more or less than they had
originally anticipated. Of the 14 that should have known, 3 did not answer, 2 wrote
that they did not know, 6 wrote “the same” (1 of which had overestimated kWh
generated), and 3 wrote “less”. An interesting result is that not a single person wrote
that it was generating “more” than expected.
Payback
With regards to payback, of the 17 people that should have known 4 did not. Given
the answers provided for energy generated the answers given have been checked
using the data from the returned questionnaires, and/or NOABL and power curves.
The responses are shown in figure 23 below.
5
Figure 23 – Owner’s estimates of the turbine’s paybacks
4
Frequency
3
2
1
0
5 9 10 12 13 14 15 20 >20
Payback period
It was possible to check 10 of these, and the results are,
• probably over optimistic: 5, 10, 12, 13, 15, 20 years,
• probably correct: 9, 14, and two of the “>20 years”.
(There is insufficient data to determine what the payback figures actually are.)
35

It is significant that the 9 year payback is the 80kW Lagerwey, and the 14 year
payback is the 4 x 20 Jacobs 29-20 turbines – these are the largest installations in
terms of total rated power out of all the ones that returned questionnaires. Both of
these received grants, and the Lagerwey is also claiming ROCs.
4.36 Reasons for installation
14
Figure 24 – Reasons listed for installing the turbine
No. of organisations listing the reason
12
10
8
6
4
2
0
Salesman
"County initiative"
Network effect
Financial reasons
To test the turbine
General education
Organisation's image
Reasons for installation
Environmental reasons
Environmental education
Two organisations were unable to provide answers.
“Network effect” means that they knew somebody who had one. “County initiative”
presumably means the decision was mandated from the county council (this person
did not list any other reasons).
Given that the majority of the institutions are educational in some way (including the
environment centres), it is not surprising that 13 of them (76%) list “environmental
education”. Given that they are all environmentally conscious, neither is it surprising
that 12 (71%) list “environmental reasons”. (Only one organisation did not list either
36

“environmental education” or “environmental reasons”, and that was the one that
listed “county initiative”.)
Relevant to the economics in Chapter 5, only 2 (12%) listed financial reasons.
The fact that nobody selected “salesman”, might tell us that up to now wind turbines
have been marketing themselves, without the need for initiative from manufacturers.
4.37 Obstacles to installation
Frequency
16
14
12
10
8
6
4
2
Figure 25 – Owner’s rating of the difficulty in overcoming obstacles
Almost insurmountable
Difficult
Small problem
No Problem
Actually helped
0
Planning issues Connecting to the grid Neighbours Rest of local
community
Potential obstacle
8
7 people (44%) had some problem with planning, 7 (50%) had a problem in
connecting to the grid, 5 (29%) had a problem with neighbours, and 2 (12%) had a
problem with the rest of the local community. Only planning and the local
community managed to help installations.
8
With graph LMU above, it is important to note that 3 people did not answer planning, 5 did not
answer regarding grid-connection (2 because their turbines are off-grid), 2 did not answer neighbours
or local community.
37

4.38 Turbine problems & after sales service
8 of the 19 installations (42%) suffered a technical problem.
It should be noted that all of the problems were different. They were:
• blade broke off
• tail fell off
• problems with a power supply unit
• gearbox problems
• generator problems
• inverter problems
• mast was badly finished and turbine kept sticking in one position
• lightning strike put it out of commission for 2 weeks
There is insufficient data to draw conclusions on the quality of any of the individual
products.
In total 5 people (26%) complained about the after sales service they had received. 4
of these had had problems that’d needed fixing, so 50% of those who had had
problems complained about delays in getting them fixed. This is despite the fact that
no question on “after sales service” was asked.
4.39 With hindsight, would they install a small wind turbine again?
Of the 16 people who were able to answer this question, 100% said that they would
make the same decision again – although 2 (13%) said they would choose a different
turbine (without the questionnaire prompting them). Both of these customers had had
technical problems with the turbine and had experienced poor after sales service.
38

4.4 Analysis of results
4.41 Of all the installations found
BRE estimates there are 700 odd mini (>0.5kW &

4.42 Of the returned questionnaires
Demographics
So far, most installations have been made by people who are environmentally
conscious. Nobody is installing them solely because of financial reasons.
Turbine locations
The urban sites with open spaces are being developed first. This is unsurprising, as
this kind of installation is well-established, and there are relatively good wind regimes.
People’s perceptions of the turbine
Few people find these small wind turbines visually stunning. Although it is possible
that some people will prefer the design of the newer models, e.g. Swift, XCO2, Wind
Dam, etc, and this could potentially help the small wind industry. Nevertheless, the
results show that visual appearance need not be an obstacle to installation of small
wind turbines.
The vast majority of people are happy with their wind turbines.
It is fortunate that the turbines are believed to be safe, but it is hard to say on what
basis the people rated their turbines as safe. At present there is limited health and
safety guidance for small wind turbines.
There are a wide variety of opinions on the amount of noise these turbines make, and
no apparent correlations with turbine type or location. There could be several reasons
for this – relative background noise, distance the owner is accustomed to being from
their turbine, or differences in the owner’s hearing.
The change in perception for neighbours & community between before and after an
installation is remarkable, and very good news for the industry. Such evidence could
truly help the small wind industry, showing that their products are ‘popular’.
Therefore, negative feedback from a community or neighbours before an installation
may well be due to an overreaction or lack of knowledge. Taking them to see a
working small wind turbine could be an excellent way to assuage their fears.
Economics & lack of knowledge of turbine operators
To date, the existence of grants has been very important for the installation of small
wind turbines. It is likely that without grants the number of installations would
40

significantly drop. This is to be borne in mind given that Clear Skies will end in
March 2006, and that there is no guarantee of a smooth transition period to the Low
Carbon Buildings Program or of its form.
With regards to generation estimates, it is interesting that not a single person wrote
that the turbine was generating more than expected – this would have been the case
with large wind turbines, where manufacturers often underestimate their performance
so as to please customers (Gipe, 2004). Small wind turbine manufacturers may be
overestimating performance or relying on incorrect wind speed data for those
locations (e.g. NOABL data is widely used by the industry, but see comments on it in
Chapter 5).
Over optimism on payback times shows lack of knowledge once again, but it also
shows that the economics are worse than people anticipate/calculate. Whether or not
this will lead to disappointment remains to be seen.
It is hard to tell if making the paperwork for claiming ROCs easier could significantly
impact on the number of installations made.
Obstacles to installation
Connecting to the grid and planning are the biggest potential obstacles to installing
small wind turbines. Neighbours and local community tend not to be much of a
problem. (There is not enough data to see if initiatives like PPS22 have had an impact
yet.)
Hindsight
Despite the complexity of installing a small wind turbine, or the expense, or the
technical / after sales problems many of these people have had, they would make the
same decision again with hindsight. Exactly why is unclear from this data.
Overall
Overall the results are positive for the small wind turbine industry, but it has serious
issues to contend with:
• their products need to appeal to people who are not just
environmentally conscious, or interested in environmental
education
41

• the industry needs to be able to survive any potential hiatus in
Government grant programs
• connecting to the grid and planning need to be easier
• the finished products need to be less problem-prone
• after sales service needs to be improved
42

5. ECONOMICS
This section of the report covers the economics of small urban wind turbines for a
school in Scotland, a typical domestic situation in the south east of England, and some
large buildings in London. It gives an assessment of the economic viability of small
urban wind.
All of the economic assessments in this chapter should be used as a guide only.
5.1 Methodology
A spreadsheet was created to model the economic data. It uses standard discount
analysis to calculate the net present value and payback. It also estimates the energy
the turbine could produce using the power curve and a Rayleigh distribution. Power
curves are assumed to be accurate. 10
Appendix I shows the variables included in the model.
Sensitivity analysis is also used to determine the sensitivity of the economic situations
to the variables. To do this it is necessary to pick a base case where the values of all
the variables are taken to be equal to 1, and then the effect that different fractions (say
0 to 5) of each variables has on the Levelised Production Cost (LPC) of energy is
shown. The result is a ‘spider diagram’, with the lines converging on the base case.
The LPC is the present cost of the energy from the turbine given the costs it has and
income it provides over its lifecycle (assumed as a 20 year period). LPC does not
need to make any assumptions about the electricity tariffs, including the future
evolution of electricity prices – but in assessing economics one can consider those
factors once the LPC is calculated.
10 Recall that power curves are from manufacturers and not from independent testing.
43

Although 7 of the people who returned questionnaires on their installation agreed to
answer more questions on the economics, only 1 person did. This means that limited
data is available on the real breakdown of costs of actual installations. 11
No modelling can be done on the Windsave, as neither the power curve nor
generation estimates at different AMWSs are available in August 2005.
5.2 Estimated installed costs per kW e for turbines
Based on the information sources, estimates for installation costs of turbines are
shown in Appendix J. Figure 26 below is the graphical representation of this data.
Clear Skies say that a typical system cost is 2500-5000 £/kW (Clear Skies, 2005). As
can be seen, many estimates of turbine costs fall within this band. In figure 26 below
the Clear Skies estimate is next to the y-axis.
Estimated cost per installed kW, £/kW
12000
10000
8000
6000
4000
2000
0
Figure 26 – Estimated turbine installed costs in £/kW
Clear Skies estimate
D400
Surface Power
Windsave
Swift (now)
Swift (projected)
Proven 2.5kW (ground)
Proven 2.5kW (building)
Turbine type
Iskra
Proven 6kW (ground)
Proven 6kW (building)
Proven 15kW
Gazelle
In figure 26 above the error bars show the full range of installed costs that the
research has found for each kind of installation, and the heights of the columns
11 However, many other sources of data were utilised, as outlined in Chapter 2.
44

epresent the average of the extremes of those ranges. There was insufficient data to
try and gauge the probability that an installation might have a given cost.
There is more data for some installations such as the Proven 2.5kW (ground-mounted),
than others, meaning the extremes for installed price are broader. This is because the
installed cost of a turbine depends a great deal on individual site factors. Some of the
other installation costs might show the same range of extremes if more data were
available.
Building-mounting Proven 2.5 and 6kW turbines is not significantly more expensive
than ground-mounting them.
The Windsave is the cheapest turbine per installed kW, but this is the manufacturer’s
estimate and it is not yet being sold at this price. Very few installations exist, so the
price cannot be confirmed and may be subject to change.
Surface Power’s turbine is a do-it-yourself kit which may explain the low cost, but as
with the Windsave there is very limited data available apart from that supplied by the
manufacturer.
Plotting a graph of £/kW against rotor diameter shows no significant correlation, due
to a lack of data (particularly with turbines of a higher rotor diameter).
45

5.3 St. John Bosco School, Renfrewshire
Figure 27 – John Bosco School’s turbine and its location
© St John Bosco School © www.multimap.com
This analysis is based on an actual installation of a Proven 2.5kW at St. John Bosco
School. The school can be seen on the map in figure 27. It is in “Erskine”, the
westernmost part of Glasgow.
AMWS
The school estimates their annual energy production at 8,600kWh per year (Appendix
G). This corresponds to an AMWS of 7.15 m/s.
At 45m above ground level, NOABL estimates an AMWS of 6.50m/s, at 25m 5.8m/s,
and at 10m 5m/s. The turbine’s mast is 11m high but it is also on a hill, and the
location is near the sea which might make it windier than NOABL predicts. However,
considering how local topography affects NOABL, 8,600kWh should be regarded as
an optimistic estimate. (BWEA, 2005)
Tariff
The school have a net metering arrangement with Scottish Power, so they buy and sell
electricity at 6.15p/kWh. Net metering is the equivalent of offsetting 100% of
imported electricity costs.
46

Economics
They do not claim ROCs (Appendix G).
Total project costs were £25,000, but grants worth £18,000 were obtained from two
sources. (EST, 2005a) The remaining £7,000 was shared with the Local Authority.
The school estimated the payback time of their Proven 2.5kW to be 13 years.
Assuming the school paid £5,000, and a 4% discount rate, and 0% annual change in
electricity prices, gives the same payback as the school estimated.
Figure 28 below analyses the sensitivity of the economic situation the school believes
they are in to changes in various parameters.
Table 11– base case of the school for LPC sensitivity analysis
Energy generated 8,600kWh
School’s investment £5,000
Discount rate 4%
Annual maintenance
costs
ROCs claimed?
£180
No
47

Levelised Energy Cost £/kWh
0.7
0.6
0.5
0.4
0.3
0.2
Figure 28 – LPC sensitivity analysis for John Bosco School
Energy generated
School's investment
Discount rate
Maintenance costs
ROC value
0.1
0
0.1 0.4 0.7 1 1.3 1.6 1.9 2.2 2.5 2.8 3.1 3.4 3.7 4 4.3 4.6 4.9
Fraction of case study's situation
In figure 28 above, the school’s LPC is most sensitive to changes in energy produced.
If the turbine generates less than they believe (which is likely), they will effectively
be paying more for their energy.
The LPC is also quite sensitive to the investment that the school made (5 on the x-axis
is equivalent to the school paying the full cost of the turbine 5 x £5,000 = £25,000).
The LPC is less sensitive to the effects of discount rates and annual maintenance.
As the school is not claiming ROCs these have been calculated in a different way.
Where the fraction is ≤1 then ROCs = 0, then it is increased proportionally until at 4
ROCs = £45. If the school started claiming ROCs today, then it would be the
equivalent of the LPC being at 4 on the ROC graph. But if the value of ROCs were to
then fluctuate the effect this would have on the LPC is also shown.
Changes in turbine model also affect the economics significantly. Below, in table 12
and in figure 29 the LPCs for different turbine types at this location are shown.
Given the grant situation with the school is complex and would have changed had
they opted for a different turbine, represent the full costs of the turbines are
represented here.
48

Table 12 – estimated installed costs & LPCs for turbines at John Bosco School
Proven
2.5kW
Iskra
5kW
Proven
6kW
Proven
15kW
Initial cost, £ 25000 27510 32570 53602
yield, kWh 8600 18221 22539 56576
LPC, £/kWh 0.214 0.111 0.106 0.070
The reasoning behind the estimates for the different turbine costs for this situation can
be found in Appendix J.
Figure 29 – Estimated LPCs for different turbines installed at John Bosco School
0.25
0.2
LPC, p/kWh
0.15
0.1
0.05
0
Proven 2.5kW Iskra 5kW Proven 6kW Proven 15kW
Turbine type
Assumptions made in calculating the LPCs:
• Project lifetime of 20 years
• No grants
• No maintenance costs
• No ROCs claimed
• Discount rate of 4%
• AMWS of 7.15m/s
The overall economics would have been significantly better if the school had opted
for a larger turbine. The improvement in LPC from a Proven 2.5kW to the other
turbines exceeds the bounds of error, and so may the improvement from a Proven
6kW and a Proven 15kW. However, from the results obtained, no difference can be
assumed in the economics of an Iskra 5kW and a Proven 6kW.
49

5.4 A traditional house in central Reading, Berkshire
This analysis is to assess the feasibility for domestic small wind turbines in a typical
inland urban site in the South East of England – the large town of Reading, in
Berkshire. Reading has been chosen because wind speed data is available for it. 12
The turbines (for which data is available) that might be appropriate for an inner-city
house are:
• Eclectic’s D400
• Surface Power’s
• the Swift
The highest point of a typical house in central Reading is ~12m high. Therefore, the
rooftop turbines could have a hub height of ~13-14 metres above ground.
As Surface Power turbines cannot be roof-mounted (Appendix A), it is assumed that
they could be installed on a 13 or 14m mast (or higher) provided potential owners
have a large enough garden. However, this is much less convenient than a roofmounted
installation.
12 It has also been chosen because it is based on a real situation. Dr. Jonathan Gregory – who works in
climate change science – is interested in installing a small wind turbine on his house at this location.
50

Location
Below is a map of central Reading. The residential areas principally consist of
closely built houses, where buildings rarely exceed 12m in height.
Figure 30 – Map of central Reading
© www.multimap.com
AMWS
The Meteorology Department of Reading University (based in the Whiteknights
campus visible on the map) have collected extensive data from an 8m mast and
estimate an AMWS of 2.8m/s (Ken Spiers email, 18/8/05).
However:
• 8m is lower than a turbine would probably be placed
• the mast is (effectively) in a field in the middle of Reading
• most houses are surrounded by houses of the same height
On balance, 2.8m/s is a relatively good guess for a turbine in this area, given that the
first of these factors should mean that the turbine receives more wind while the next
two should mean it receives less wind, and given that there is no other data available
apart from NOABL.
51

NOABL estimates that the wind speed 10m above ground would be 4.8m/s here –
indicating its unreliability where local topography is complex.
Tariffs
A green electricity tariff might be 7.56p/kWh. 13
Electricity consumption
Typical annual electricity consumption might be 2,900 kWh/year. 14
Economics
Table 13 – Estimated economics of residential turbine installations in Reading
Turbine type Annual Installed Payback Possible Payback
energy yield, cost
kWh
w/out
grant, years
grant with grant,
years
D400 110 £2,200 63 Not eligible XXXXX
Surface Power 178 £1,518 44 Not eligible XXXXX
Technologies
Swift 474 £5,000 49 £1,500 41
Assuming conditions synonymous with best case scenario conditions:
• none of the electricity is exported
• annual maintenance costs are zero
• discount rate of 0%
• 4% annual increase in energy costs
• Best case installation costs for each turbine
None of the turbines are exporting enough energy to qualify for ROCs.
13 Based on Jonathan Gregory’s bills.
14 Based on Jonathan Gregory’s electricity consumption.
52

The Swift is the only one that could qualify for a grant as the D400 and Surface
Power’s turbines produce too little power. (Clear Skies, 2005)
Even with a grant, the Swift payback is 41 years. This is considerably greater than the
expected lifetime of the turbine.
Therefore, it would be uneconomic for the homeowner of a typical house in Reading
to install any of these turbines.
To raise public awareness one could install a D400 relatively cheaply, but it would
only reduce their annual energy bill by £8.32 (at these tariffs).
For the D400 to payback within 10 years at this location under the highly favourable
conditions above, it would need to cost £99 or less. While at £2,200 the D400 takes
13 years to payback, even with an AMWS of 10m/s and including ROCs at £45/MWh.
Surface Power’s turbine generates its maximum amount of energy at an AMWS of
about 9.5m/s, and in the best case conditions above, it can payback in 11 years. It can
not benefit from ROCs as it is intended to be an independent off-grid supply. 15
With the best case cost price for the Swift of £3,500 after grant, and including ROCs
at £45/MWh, it can payback within 10 years with an AMWS of 5.5m/s.
But with the current cost of the Swift of £8,500 after grant, including ROCs, to
payback within 10 years requires an AMWS of 9m/s.
Figure 31 below is LPC sensitivity analysis, for a Swift, where the base case of 1 is:
Table 14 – Base case for residential Swift installation in Reading, for LPC
sensitivity analysis
Energy generated 474kWh
Amount invested £3,500
Discount rate 4%
Annual maintenance
costs
£75
15 As explained in Appendix A, Surface Power market their turbine (and solar panels) with a deepcycle
battery, inverter, and plug sockets, and intend for this arrangement to be off-grid – so that a
homeowner may operate some of their appliances from it whilst leaving the rest of their appliances
connected to the grid, thus reducing their bills.
53

Levelised Energy Cost £/kWh
Figure 31 – LPC sensitivity analysis for the installation of a Swift on a house in
Reading
8
Energy generated
7
Amount invested
Discount rate
6
Maintenance costs
5
4
3
2
1
0
0.1 0.4 0.7 1 1.3 1.6 1.9 2.2 2.5 2.8 3.1 3.4 3.7 4 4.3 4.6 4.9
Fraction of base case parameters
The LPC is most sensitive to changes in the energy generated, and the installation cost.
Even a small improvement in either can significantly improve the economics. The
line for ‘amount invested’ could stop where the fraction is 3.43, because that reflects
£12,000. The furthest extent for the line of ‘energy generated’, reflects an AMWS of
5.2m/s.
The annual maintenance cost of £75 has been guessed, but once the maintenance costs
for the Swift are known (whether they are £0 or £375) the LPC can be deduced from
this graph.
In the base case the Swift generates insufficient energy to qualify for ROCs, hence
there is no graph for it.
54

5.5 Large buildings in London – RIBA and the Aylesbury Estate
This analysis looks at theoretical costs of two projects in London. The RIBA (Royal
Institute of British Architects) who were interested in installing a wind turbine on
their roof, 16 and the Aylesbury Estate in Southwark should have some wind turbines
installed on the rooftops of their tall tower blocks. They have also been chosen
because wind speed data is available for them.
Locations
Figure 32 – Map of RIBA’s location in London
© www.multimap.com
In the map above, the RIBA building is just off the A4201, W1B 1AD. It is slightly
taller than the buildings in the surrounding area.
16 They were refused planning permission for such a project prior to PPS22 and the GLA’s support, but
may try again.
55

Figure 33 – Map of Aylesbury Estate’s location in London
© www.multimap.com
The Aylesbury Estate comprises much of the area south of East Street, e.g. around
Thurlow Street, SE17 2UZ. It is Europe’s largest estate.
AMWS
Data measured from the rooftops of the RIBA building and a tower block of Portland
Estate (near Aylesbury Estate) found the AMWSs to be 3.4m/s (Thomas, 2003) and
8m/s respectively. 17 (Nick Banks email, 4/8/05)
The difference in wind speeds could be due to differences in the relative height of the
RIBA building and its surroundings, and the Portland Estate tower and its
surroundings. The Portland Estate tower could also be much higher.
At RIBA NOABL estimates the AMWS to be 5.7m/s at 25m height (the RIBA
anemometer was 36.5m high – Thomas 2003), and at Aylesbury Estate at 45m height
it finds it to be 6.1m/s – although the towers could be higher than this.
17 Southwark Council who conducted the measurements take no responsibility for any conclusions that
might be drawn from the use of this data.
56

Tariffs
A tariff of £0.06/kWh is used. Although the Aylesbury Estate towers are residential
the electricity may be used by the landlord, and if not then it will underestimate the
turbine economics as domestic tariffs are higher (e.g. £0.07/kWh).
As both buildings are large it is unlikely any electricity would be exported.
Turbines chosen
The D400 is too small, and Surface Power’s turbine cannot be roof-mounted. Even if
there were data the Windsave would not be a good choice for the Aylesbury Estate
given its low cut-out wind speed (see Chapter 3). The Swift and Proven 2.5kW are
appropriate. The Proven 6kW might be too large, but this would depend on the
outcome of a structural survey, so it will be considered.
Economics
Installation costs for building-mounting the three turbines can be found in Appendix J.
For the Proven 2.5kW & 6kW the most expensive estimates of £21,000 and £26,000
will be used. Swift estimates show a far greater variation in price: £5,000-12,000 due
to the projected price decrease over the next 12-24 months. Both of these prices shall
be assessed as it is uncertain if their target price will be achieved.
Table 15 – Economics of roof-mounted turbines on RIBA & the Aylesbury
Estate
RIBA
Aylesbury Estate
Annual Payback, Annual Payback,
energy yield, years energy yield, years
kWh
kWh
Proven 2.5kW 1,497 82 10,188 10
Proven 6kW 4,183 32 26,140 5
Swift 1.5kW,
33 5
best £ case
Swift 1.5kW,
worst £ case
798
89
5,466
11
57

Assumptions:
• grants cover 50% of the total installed cost
• collecting ROCs at £45/MWh
• only offsetting imports
• discount rate 4%
• annual increase in electricity price 1%
• no annual maintenance costs
Altering these conditions slightly, if the Proven 6kW for Aylesbury Estate didn’t
collect ROCs it would payback in 10 years, if it didn’t receive any grants it would
payback in 12 years, and if it didn’t receive any grants or ROCs it would payback in
24 years. 18
Figure 34 below is a sensitivity analysis for some parameters for the base case of a
Proven 6kW on one of the towers of the Aylesbury Estate. The base case of 1 is:
Table 16 – Base case for roof-mounted Proven 6kW on the Aylesbury Estate, for
LPC sensitivity analysis
Energy generated 26,140kWh
Amount invested £13,000
Discount rate 4%
Annual maintenance
costs
ROC value
£180
£45/MWh
18 The expected lifetime of a Proven 6kW is 20-25 years (Appendix B).
58

Levelised Energy Cost £/kWh
Figure 34 – LPC sensitivity analysis for a roof-mounted Proven 6kW on the
Aylesbury Estate
0.5
Energy generated
Amount invested
0.4
Discount rate
Maintenance costs
0.3
ROC value
0.2
0.1
0
0.1 0.4 0.7 1 1.3 1.6 1.9 2.2 2.5 2.8 3.1 3.4 3.7 4 4.3 4.6 4.9
-0.1
-0.2
-0.3
Fraction of base case parameters
Any large increase in electricity generation or ROC value from the base case is
unlikely so should be ignored. Negative LPCs shown in these instances are a result of
large amounts of money being made from ROCs.
From the base case’s proximity to an LPC of 0p/kWh, it can be seen that it is
economic.
For the base case, £180 was chosen for the maintenance costs as that is the known
maintenance cost for a Proven 2.5kW (see John Bosco School in Appendix M), and
the maintenance cost for a building-mounted Proven 6kW will be at least as large.
Effects of an increased maintenance cost on the LPC will be slight.
5.6 Analysis
All of the sensitivity analyses show a greater sensitivity to changes in AMWS than for
any other variable. Therefore this is the most important consideration in siting an
urban wind turbine. The amount invested is also highly important, and therefore
grants should be sought whenever possible.
59

In the urban environment one is far more likely to encounter a good AMWS at the top
of a tall building which is considerably taller than the surrounding buildings, e.g. the
tall tower block of Southwark’s Portland estate. In this kind of location urban wind is
economic – although it still requires grants and/or ROCs. These are the locations in
any city that need to be taken advantage of.
Given the comparison with RIBA, tall tower blocks may be the only windy locations
in a place like London, although windier cities (e.g. Edinburgh) may have many more.
Wind turbines for houses in places such as Reading (and probably also London) won’t
be successful on the basis of economics, and won’t generate a significant portion of
energy either because of the low AMWSs. And at present, the only wind turbine (for
which figures are available for) which will be economic with an achievable AMWS
(5.5m/s), is the Swift at its projected price (and assuming a grant). The other turbines
aimed at the domestic market (D400 and Surface Power’s) need to drop in price
and/or other economic factors need to change.
With regards to wind data, more work needs to be done to determine what an AMWS
will be at a particular urban site. The difference between the RIBA and Portland
Estate figures indicates an extremely high degree of variability in the urban
environment. More data could be collected, and computer models could be developed
that would make predictions. One should not rely on NOABL in the urban
environment because it does not take into account local topography, and will very
likely give overestimates for wind turbines.
To help put small wind into context, SEA estimate that there are ~4000 or so tower
blocks in the UK. If on average 10kW were installed per block, that gives a rated
capacity of 40MW. The equivalent of about 20 large wind turbines.
Although it would be interesting to compare the economics of the turbines with their
cut-in wind speeds, there is insufficient data to do so.
60

6. CONCLUSIONS
State of the art
1. While “the larger HAWTs” have urban and rural uses, the 4 “smaller HAWTs
aimed at the urban market” all came on the market in 2005, while there are
another 8 prototypes being designed for the urban market. Therefore, many in
the industry in the UK & Ireland believe small wind turbines in the urban
environment (especially building-mounted ones) have great potential. As the
majority of these are VAWTs, many of them also believe that the advantages
of VAWTs (particularly ones that use the lift force) will outweigh their
disadvantages. It is hard to tell if so many new products are justified; it will
depend on the ultimate development of the market. The success of VAWTs
also depends on how successful the HAWTs are at cornering the market in the
intervening time – although VAWTs may always find a niche where buildings
have focussed the airflow and made it extremely turbulent.
2. Cut-in and cut-out wind speeds should be considered given the turbine’s
environment. Turbines with a high cut-in (e.g. the Gazelle) should not be
placed in sites with a low AMWS (e.g. ground-level of central Reading).
Turbines with a low cut-out (e.g. Windsave) should not be placed in sites with
a high AMWS (e.g. on high rooftops).
3. Judging from Sagrillo’s method, the HAWTs intended for the urban
environment are built to withstand turbulent conditions. It remains to be seen
if they can withstand the levels of turbulence found in such sites.
4. It is not certain that manufacturers can be trusted to provide impartial technical
data on their products. An independent small wind turbine testing centre (as
there is with larger wind turbines) would be useful. A standard rating for
small wind turbines similar to that with photovoltaics would be useful for
customers. The rating could potentially have the form of energy generated per
year at different AMWSs. This can be derived from power curves, but this is
not a customer-friendly format.
61

Installations
5. There are probably at least 100 installations of wind turbines

production or new manufacturing techniques would improve the economics.
Other components such as inverters would also need to drop in price.
9. A combination of factors is necessary to make economics viable in most
situations. The economics are especially sensitive to changes in the AMWS.
10. The evidence suggests that NOABL wind speeds are overestimates for the
urban environment. It is possible that reliance on NOABL is one aspect that
has led to so many turbine owners overestimating the economics. Remedies
for this include more publicly available wind measurements from urban areas
(especially rooftops), or wider use/development of reliable software.
11. At current prices, the wind turbines for the domestic market are uneconomic.
It is hard to envisage how this market will be successful unless prices drop
and/or other conditions change (e.g. tariffs).
12. Given the AMWS measured on the Portland Estate, rooftop installations on
high tower blocks could be extremely promising. Some more research and
experience of roof-mounted installations is required, but if grants and/or ROCs
remain available and high AMWSs are found to be widespread on tower
blocks, then installations of this type could rapidly become a feature of the
urban landscape.
13. However, given the measured Reading & RIBA wind speeds much of the
urban environment may be unsuitable for small wind turbines to be
economically successful.
14. Micro turbines may find applications where they are more economic than
alternatives as is happening with photovoltaics – e.g. temporary road works
signs, bus stops.
15. It is uncertain if manufacturers can be trusted with economic information until
their product is actually for sale at that price, e.g. comparing the price of the
Windsave to Eclectic’s D400, and their rated powers.
63

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71

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72

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73

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74