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Appendix 1

The Potential Visual Impact of Wind Turbines in relation to distance

1 The 'Thomas Matrix'

In September 1996 an attempt was made by Mr Gareth Thomas, the Planning Officer of Montgomeryshire (arguably the local authority with the greatest experience of dealing with wind power station proposals) to define the potential visual impact of wind turbines by descriptors which could be assessed in the field, and which, with repeated observation, should produce a degree of observer consistency. The approach assumes good normal visibility, and is intended only to be a general guide, especially at the margins of each band, recognising the importance of local conditions, viewing direction, turbine angle and the scale and nature of the landscape context. The Matrix incorporates the following nine bands of visual impact ranging from "dominant" to "negligible", identified as 'A' to 'I' in the Table below.

2 The revised Thomas Matrix

The Thomas Matrix was originally determined in respect of the 25 and 31m hub machines at Cemaes and Llandinam (overall height 41.5 - 45.5m respectively: significantly less than that of turbines subsequently constructed throughout the UK). Mr Thomas concluded from this that "15km is considered to be the appropriate radius distance for study", although many Zone of Visual Influence (ZVI) maps in Environmental Assessments have employed a much smaller radius (even for much larger turbines). Several hundred field observations have since been carried out in the visual hinterlands of constructed wind power stations throughout Britain by Geoffrey Sinclair of Environment Information Services to test the Thomas Matrix and the relevant ZVI threshold. Initially this exercise was confined to the two installations in Montgomeryshire where the Thomas Matrix was developed, and then extended to others using similar-sized machines. This established broad agreement with Mr Thomas' descriptions of visual impact, but found that his original distance bands were rather conservative. Minor amendments were made to his distances, as shown by the results in the second column of the Table below headed the "Revised Thomas Matrix".

3 The Sinclair-Thomas Matrix

The Thomas approach was extended to viewpoints around other wind power stations which used larger turbines in order to establish the extent to which distances for each visibility band (and thus the appropriate ZVI radius) needed to be extended in relation to the increase in turbine size. In practice, the larger turbines used in most installations constructed since the 41-45m '1st generation' have tended to cluster around 52-55m, and the results for these are shown in the first column of what may now be called the 'Sinclair-Thomas Matrix'. Provisional results from the largest turbines subsequently built (the four 750kW 70m machines at Great Eppleton, Houghton-le-Spring, County Durham) have also been used to construct a further tentative set of distances. A projected series has been added to extrapolate the sequence in relation to the latest proposals for the 1.5MW 95m turbines at Mynydd Hiraethog, North Wales.

THE 'THOMAS' AND 'SINCLAIR-THOMAS' MATRICES to estimate the potential visual impact of different sizes of wind turbines

                                           Notes (as at March 1999):
* Only four 70m turbines have yet been constructed (at Great Eppleton, Co. Durham).
** Data extrapolated for 95m 1.5MW turbines (as proposed at Mynydd Hiraethog, Conwy)

References

1 1995 Policy on Renewable Energy Installations, CPRW, 1995

2 Wind Energy - Power for a Sustainable Future: Policy Statement of the British Wind Energy Association, 1996: BWEA, 1996

3 Memorandum by the British Wind Energy Association to the House of Commons Trade and Industry Select Committee Aspects of Energy Policy Inquiry, January 1998

4 Offshore Wind Energy - Building a new industry for Britain Greenpeace / Border Wind, June 1998

5 Pla'r Twrbinau Gwynt: Ple ar ran y Tirlun (Wind Turbine Blight: a Plea for the Landscape) - CPRW, April 1997.

6 Wind Energy and the Landscape: a Joint Statement by APRS, CPRW, CNP, CPRE and the Ramblers' Association - May 1997; accompanying CPRE Press Release 35/97 "Groups unite in calling for new direction for wind power policy"; and letter to the President of the Board of Trade dated 15 May 1997

7 Call for a Change of Wind Direction: Response by the Countryside Commission to the Government's consultation on the Fifth Round of the NFFO, October 1997

8 Submission by CPRW to ETSU Research Study The Cumulative Effects of Wind Turbines (CEWT) February 1999

9 Wind Turbines in the Welsh Landscape - Looking for the Way Forward: Seminar organised by the Countryside Council for Wales, February 17th 1999 (proceedings in course of preparation, March 1999)

10 Public Inquiry into the extension of the Cemaes wind power station (Cemaes B) Montgomeryshire, Proofs of Geoffrey Sinclair (CPRW/GS/023) and Merfyn Williams (CPRW/MW/025) July 1998

11 The formulation and operation of policy on wind power and its interaction with the planning system: Evidence to the House of Commons Trade and Industry Committee Inquiry: Aspects of Energy Policy - CPRW, February 1998

12 Appeal and Application by National Wind Power Limited (Barningham High Moor) ref APP/W1335/A/97/285005, Government Office for the North East, November 1998.

13 Renewable Energy: Dismissal of National Wind Power's Appeal at Barningham High Moor raises wider issues for government policy - Environment Information Services News Release, 20th November 1998.

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