siting of wind turbine

wazzoraybelle

We are looking into the viability of a wind turbine for our site, however the only place we would consider putting it is approx. 5 metres from a 38 metre cliff. While I know the cliff will create an updraft and turbulence. I'm wondering if the turbine is close enough to the cliff and the pole is high enough ,say 15m, will the turbine be above the turbulent wind?

Is there a device that can measure turbulence? I believe an annometer can't.

At present there is a 20 metre timber pole where I want to put the turbine and there is a loose cable of about 3 metres on top, even in the strongest gales the cable flies at a right angle to the pole with very little wobbling, am I right to assume that this means there is no turbulence at this height?

quentingargan

You are right that an anemometer doesn't measure turbulence. This is one reason why buying a wind turbine always has a certain amount of guesswork about what energy it will produce, particularly on a turbulent site.

Paul Gipe in his book suggests flying a kite until you notice that its tail is straight. So you might be onto the right thing in what you are suggesting. The pole itself will cause some turbulence to any streamer you try flying off it unfortunately.

I have sometimes heard that at lower heights in a situation like yours, you may even benefit from wind acceleration at a point close to the cliff. If you can get a pulley onto the top of that pole, and run a rope along the cliff face to a point some 30m away, you could hang streamers from that rope and watch what patterns of wind emerge at various heights. You may even find that 10 or 15m is a better height.

I don't know what size of turbine you propose, but bear in mind that larger turbines have the blade length to the bottom of their stroke. So if you have a 3m blade on a 10m tower, at the bottom of its stroke it is only 7m off the ground.

wazzoraybelle

Thanks for that Quentin, we're leaning towards a 2.5kw at the minute but havn't ruled out a 6kw yet.

As we are in the middle of a large renovation project and about to apply for planning we thought we might as well apply for planning for a turbine sized similar to the exemption for farms (20m to blade tip). I was thinking about putting streamers at various heights on the pole (7m, 10m, 15m etc) but your suggestion is much better.

We are in a very exposed site and would be pretty confident of a 6.5m/sec to 7.5m/sec mean wind speed. Would there be anything to gain from putting an anemometer on the site?

quentingargan

wazzoraybelle wrote: »

We are in a very exposed site and would be pretty confident of a 6.5m/sec to 7.5m/sec mean wind speed. Would there be anything to gain from putting an anemometer on the site?

There are two approaches to using an anemometer. The first is that you put it up for 12 months so you get a yearly average. The second is that you put it up for a shorter period, during which you compare its output to that at a local met station. If you know how your local wind speed and direction compares with different speeds from the local met station in the same directions, then in theory at least, you can extrapolate to get equivalent historic data for your site.

I once read a suggestion that you just put up a cheap turbine instead. That way you get electricity as well as data!

To be honest, there is always a certain amount of guess work, even with an anemometer. That's why most banks want three years of data before they fund a wind farm, and that is usually with much less turbulence than domestic sites. Most turbines get purchased on the basis of a desktop survey rather than anemometer data, which in any event doesn't take into account the turbulence. If your mean wind speed at the hub is over 6.5, then chances are that your payback time will be pretty good anyhow, so it is unlikely that you are buying a lemon!

NBW

Would a turbulent wind shorten the life span of your turbine though?

quentingargan

NBW wrote: »

Would a turbulent wind shorten the life span of your turbine though?

Yes - though some more than others, depending on the design. However, the intention (see earlier) was to set streamers to see at what height the turbulence is lowest.

wazzoraybelle

quentingargan wrote: »

I have sometimes heard that at lower heights in a situation like yours, you may even benefit from wind acceleration at a point close to the cliff. If you can get a pulley onto the top of that pole, and run a rope along the cliff face to a point some 30m away, you could hang streamers from that rope and watch what patterns of wind emerge at various heights. You may even find that 10 or 15m is a better height.

I don't know what size of turbine you propose, but bear in mind that larger turbines have the blade length to the bottom of their stroke. So if you have a 3m blade on a 10m tower, at the bottom of its stroke it is only 7m off the ground.

I havn't had an opportunity to put up streamers yet but I installed a weatherstation at 10metres on the 1st of may and it appears that the cliff is indeed speeding up the wind as the recorded speeds are higher than 4 other stations nearby, ( it has rarely gone below 10.5m/s-12m/s). One of the stations is a marine buoy with an annual average windspeed of 9m/s!!

quentingargan

wazzoraybelle wrote: »

I havn't had an opportunity to put up streamers yet but I installed a weatherstation at 10metres on the 1st of may and it appears that the cliff is indeed speeding up the wind as the recorded speeds are higher than 4 other stations nearby, ( it has rarely gone below 10.5m/s-12m/s). One of the stations is a marine buoy with an annual average windspeed of 9m/s!!

That sounds like a great site for a turbine alright.. I would still do the streamer test to avoid turbulence to promote longevity in the system. Turbulence doesn't affect the cups of an anemometer in the same way. In that situation you would be best served with a turbine designed to withstand high winds, but also capable of running in high winds, rather than one that shuts down or furls.

The extra cost of doing this is usually not justified on sites with lower wind speeds, but may well be justified on yours.