As some of you may be aware, a Shadow Flicker Assessment was included in the Tall Tree wind farm Referral documentation lodged recently.

Shadow flicker is not a topic everyone may be familiar with; recognising this, we have focused on it in previous sessions to share information and field questions. We recently received a question on why the hub height of 159 metres has been used in the study instead of the maximum hub height of 169 metres, which is mentioned in our referral. We thought it might be useful to share the explanation more broadly.

Explanation of hub height

The maximum hub height of 169 metres in our referral is based on a 163m rotor diameter with a maximum 250.5m tip height (81.5m blade + 169m hub height = 250.5m tip height). The rotor diameter refers to the width of the area swept by the rotating blades – in simple terms, double the length of a single blade.

The Shadow Flicker Assessment, however, has been conducted assuming the largest rotor diameter for which we are seeking approval for: 183m. The highest hub height that such a rotor could have, whilst still complying with the overall tip height of 250.5m, is 159m (91.5m blade + 159m hub height = 250.5m tip height).

The configuration used for the shadow flicker assessment (maximum rotor diameter with maximum tip height) represents the worst-case scenario, even though the hub height may in practice be greater. The team have put together the below diagram as an example to help explain this: 

As can be seen, the shadow zone of the bigger rotor will always be larger than (and contained within) that of a smaller rotor, even if the latter has a taller hub height. By extension, the heat-map or ‘butterfly diagram’ results will always be greater at any given point.

We hope this additional information helps the wider community with their review of the referral.

As always, the Tall Tree Project Team encourages anyone with questions to contact us directly on 1800 283 550 or at talltree@acciona.com