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9 MW

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144 MW

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111 MW

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84 MW

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• A Good Practice Guide to the Application of ETSU-R-97

– “During scoping of a new wind farm development consideration should be given to cumulative noise impacts from any other wind farms in the locality. If the proposed wind farm produces noise levels within 10 dB of any existing wind farm/s at the same receptor location, then a cumulative noise impact assessment is necessary”

– “Equally in such cases where noise from the proposed wind farm is predicted to be 10 dB greater than that from the existing wind farm (but compliant with ETSU-R-97 in its own right), then a cumulative noise impact assessment would not be necessary”

IoA Good Practice Guide – Cumulative Issues

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Cumulative Assessment

• Both schemes proposed together

• 40 dB(A) appropriate• Cumulative total within

ETSU-R-97 criteria• Grant both schemes

A - Proposed

B - Proposed

R2

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Assessment Process

• Day-time – the greater of 40 dB(A) or 5 dB(A) above background

A closer look

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Can operate at its consent

Assessment Process

• Day-time – the greater of 40 dB(A) or 5 dB(A) above background

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Assessment Process

• Day-time – the greater of 40 dB(A) or 5 dB(A) above background

Can operate at its consent

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Assessment Process

• Day-time – the greater of 40 dB(A) or 5 dB(A) above background

Cumulative total 3 dB(A) too high

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Assessment Process

• Day-time – the greater of 40 dB(A) or 5 dB(A) above background

The total is effectively the cumulative addition of the individual limits

Potential to fully utilise the limit at all wind speeds as shown is very unlikely but theoretically what has been consented

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Cumulative Assessment

• Assessment confirms cumulative total within ETSU-R-97 criteria

• Each scheme is proposed at the same time

• How can this be made to work?

– Apportion limit between schemes to meet overall requirement

– Based on logarithmic subtraction

R2

A - Proposed

B - Proposed

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Assessment Process

• Day-time – the greater of 40 dB(A) or 5 dB(A) above background

Margin?

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Cumulative Assessment

• Day-time – the greater of 40 dB(A) or 5 dB(A) above background

Limit for Scheme A

Margin

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Cumulative Assessment

• Day-time – the greater of 40 dB(A) or 5 dB(A) above background

Limit for Scheme B

Margin

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Cumulative Assessment

• Day-time – the greater of 40 dB(A) or 5 dB(A) above background

ETSU-R-97 criteria met

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Cumulative Assessment

• Fair apportionment of the limits IF both schemes are proposed at the same time

• Example given– Margin exists between total cumulative noise levels and the limit – Zero margin – process still works

• Only works where schemes are proposed at the same time!• Other situations

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Cumulative Assessment - 35 to 40?

• Choice of the fixed part of the day-time noise limit should be evaluated based on the total number of turbines in the vicinity

• Choice within an existing consent of 35 dB(A) should not be fixed for all time for subsequent developments → 40 dB(A) may be appropriate based on 3 aspects given in ETSU-R-97

• If the small scheme was consented choosing 35 dB(A) this may not remain appropriate for the combined total

R2

built & operatingSmall scheme

A - Proposed

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Cumulative Assessment – Further Examples

• Scheme A has consent basedon 40 dB(A)

• Scheme B may add to total cumulative noise levels

• Scheme B may need to be limited to10 dB(A) below Scheme A consent limits(e.g. 40 dB + 30 dB = 40.4 dB)

• This may not be necessary where Scheme A cannot feasibly utilise all of the consent noise limits

R2

A - Consented

B - Proposed

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Cumulative Assessment – Further Examples

• This may not be necessary where Scheme A cannot feasibly utilise all of the consent noise limits

• Where noise from Scheme A is ‘controlled’ by another receptor location (R3 in this case)

R2

A - Consented

B - Proposed

R3

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Cumulative Assessment – Further Examples

• This may not be necessary where Scheme A cannot feasibly utilise all of the consent noise limits

• Where noise from Scheme A is predicted to be sufficiently below the consent limit

– May be due to separation distances as shown

– Caution to model using the correct turbine sound power levels for the operating wind farm

R2

A - Consented

B - Proposed

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Cumulative Assessment – Further Examples

• This may not be necessary where Scheme A cannot feasibly utilise all of the consent noise limits

• Where receptors cannot be downwind of both schemes at the same time

– Clear case when 180 degrees apart– Caution with assumed directional

attenuation as much less certain

A - Consented

B - Proposed

R2

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Cumulative Assessment – Further Examples

• This may not be necessary where Scheme B for an extension to Scheme A by the same operator and forms one larger wind farm

– Demonstrate that the extended scheme can still meet the original consented limits

R2

A - Consented A Extension

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Cumulative Assessment – Further Examples

• Small wind turbines - often consented without full ETSU-R-97 assessment orETSU-R-97 noise limits

• ETSU-R-97 criteria may already be exceeded by small turbines at nearby dwellings

• Small wind turbines should not preclude wind farms or visa-versa

A - Proposed

built & operatingSmall wind turbine

R2

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Conclusions

• ETSU-R-97 criteria apply to cumulative noise from all wind turbines• Potential for schemes to ‘use up’ the ETSU-R-97 limit• Proposed together – ‘fair’ apportionment of limits may work

– Consistency in modelling– Reasonable operating margin → not restricted to candidate turbine

• Where not proposed together– Evaluate 35 to 40 choice– May require 10 dB down noise limits in some cases– Directional factors may be relevant– Operating schemes may not be able to ‘use up’ limit (needs to be fully

considered)– Other ‘controlling’ receptor locations may be relevant– Extensions allow ‘holistic’ management of noise– Micro/small turbines should not preclude wind farms or visa-versa

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Thank you