Why are the wind turbines not always turning?

Posted By: Wera Hobhouse
Date Posted: 20/11/2009

The wind turbines up on Scout Moor have been up for a while and it is easy to follow their daily operation. It seems that for quite a lot of time they don’t seem to be turning, so I contacted Peel Energy and asked for a meeting to find out why, and ask them some other probing questions. Peel Energy was happy to oblige.
On a beautiful crisp November morning I was met by Richard Dibley, Senior Development Manager for Peel Energy and Len Hughes, Operations Manager for Scout Moor wind farm, who drove me straight up the muddy track past the quarry to the top of the moor. We stopped amidst the imposing structures of the 60m high columns and fantastic views for miles around. There was a lot of wind, but three turbines were not turning.
This was a good start for all my questions and here are some answers.
Every turbine is being serviced every six months –like an MOT. The service takes three working days and while the men are working up and around the turbine, it is turned off for Health and Safety reasons. I understand that the turbine is turned on in the evening when the men stop their working day.

Each turbine generates at 600volts which is increased to 33,000 volts via the turbine transformer. All 27 turbines are connected by cables in three electric circuits which all come together at Turbine 14. From here the electricity is sent to the substation in the valley where it is increased again to 132,000 volts and exported to the grid line past Ashworth reservoir.
When we see a third of all turbines not turning one of the circuits is switched off. Only when there is a complete circuit failure would all turbines stop which is rare.
So in case we see no turbine turning the most likely reason for it is that there is no wind.
I understand that Scout Moor wind farm operates at 96% ‘availability’ meaning that only 4% of the reasons why the turbines are not turning is due to mechanical or electrical failure or servicing.

But Scout Moor wind farm is operating at only 34% capacity and that is simply because of the varying strength of wind during the 24 hours of the 365 days in the year. The turbines start operating at a minimum wind speed of 4m/s (meters per second), and reach the optimum output of 2.5 MW for each turbine at a wind speed of 15m/s. The optimal output remains stable after that until wind sped reaches 25m/s, then the turbines need to be shut down for safety reasons. However 25m/s wind speed equals storm force 10.
The main reason why Scout Moor wind farm operates at only 34% capacity is because the wind speed is not often at the optimum 15 -25m /s but more often around 7-12m/s. The average daily output at Scout Moor is 1100 MW per hour, which provides enough electricity for 40,000 homes.

The higher the voltage the further electricity can travel. Because Peel Energy offers its electricity from Scout Moor at 132,000 volts and because Scout Moor is near a dense urban population with high demand, the electricity will be used directly in the local area.
So is it worth generating electricity for 40,000 homes in and around Rochdale Borough with energy that uses up an unlimited renewable resource which is readily available, leaves no waste behind and doesn’t pump thousands of tons of carbon dioxide into the atmosphere, but losing the look of a beautiful uninterrupted hill side at Scout Moor and a wild walk up the hill without coming across some man made structures?

I suspect opinions will still be divided.