Small Wind Turbines Factsheet Content Page Page Introduction 2 Microrenewable technologies 3 Measuring your wind speed 4 Why you should measure your wind speed 5 Case Study: Installing FuturEnergy turbine 8 Wind turbine planning permissions 11 Getting planning permission 12 Wind turbine building course 14 DIY wind turbines 15 Small wind turbines impact on birds 16 Wind turbines: Noise and vibration 19 Selling your electricity to the grid 20 ROCs 23 Future information and contact details 24 1 Introduction Green energy factsheets Here we have heaped together a ton of information on saving energy in your home, generating green energy, and a whole load of supporting facts on stuff like the grants available to help you get started. 2 Micro renewable technologies So you've done everything you can to save energy? What next? In this booklet we take a look at wind turbines, explaining how they work and what factors you should consider before getting started on generating your own green energy. Wind turbines These are either mounted on a pole in your garden, or in some cases fixed to your roof. A lot of different makes are now on the market, but which is best for you? And what about planning permission and grants? In this booklet you can... • Read about the options available for measuring your wind speed prior to investing in a turbine. • Find out why we recommend you should measure your wind speed with an anemometer. • Read a case study on installing the FuturEnergy turbine. • Find out more information regarding planning permission for wind turbines. • Find out about a build your own wind turbine course , as well as some info on DIY wind turbines . We also take a look the tough questions... • What affect does a wind turbine have on local bird population s? Read on to find out the facts for small wind turbines, the manufacturer’s response, and the RSPB's opinion on the matter. • Doesn’t everyone complain about the noise and vibration created by turbines ? Later we take a look at how real is this problem. Last but by no means least... • Read about selling your electricity to the grid and ROCs • To find out more information, you can contact us or visit our reviews section to find out which turbine is right for you! 3 Measuring your wind speed There are two methods you can use to measure your site's wind speed; one involves a detailed site assessment, while the second is based on modelled data. We explain more below. Measuring wind speed with an anemometer The only way to know for sure what kind of power your turbine might produce before you invest in one is take some direct wind speed measurements. Definitely worth doing. There are companies around who can come and do a really professional site assessment, but for small machines, this could end up costing as much as the turbine itself! But you can do it yourself too with a gadget called an anemometer ; a gauge for measuring the speed and direction of wind. Ideally, you'll use it to gather data over several months and seasons to get an accurate average wind speed. Decent anemometers are usually pretty pricey, so we've worked hard to bring you a range of low cost anemometers that you can set up yourself. The alternative: modelled wind speed data Alternatively, there are also ways of roughly estimating your wind speed using modelled wind speed data , but this needs to be taken with a pinch of salt. One of the easiest ways to do access modelled data is by visiting the Segen website and typing in your postcode to get back the average wind speed (in metres per second) for your house. There is also a generalised wind speed map (at 50m above ground level) at www.windatlas.dk . The Carbon Trust have also recently launched an online wind speed estimator. The problems with modelled data The figure you'll get from such modelled data will be the average for the square kilometre you live in. But there's always a lot of variation within each square km, and the information takes no account of the lower and more turbulent winds in urban areas. Have a think about where the turbine might be installed, and what might affect the wind flows. Here's a handy list of things to account for (from suggestions published by turbine manufacturers Proven Energy): • Take account of nearby trees and buildings • A site at the bottom of a valley or hollow will have a lower wind speed than the average, so adjust the average wind speed down • A site on top of a hill or knoll will have a higher wind speed than the average, so adjust the average wind speed up • The modelling does not include the effect of sea breezes, so for coastal sites add 0.5 - 1 m/s to the wind speed • For flat open countryside the model returns a more accurate result • For complicated terrain the model is less accurate. 4 Why you should measure your wind speed If you are planning to install a wind turbine it is sensible to carry out a full site assessment and measure the wind speed first, to find out how windy your potential turbine site really is. We can't emphasise this enough, because if the wind speed isn't good enough you'll be wasting your money - and with the best intentions in the world - a turbine that doesn't turn is hardly going to help your energy bills (or climate change for that matter). Winds are influenced by the ground surface of heights up t o 100 metres. As most wind turbines are likely be positioned below 20 metres this is a vital factor to consider in choosing your perfect site. So not only do you need to assess the wind speed of your area but you need to think about local factors to your site such as the roughness of the surrounding terrain and obstacles such as trees and buildings might affect the output. To fully take such factors into account you really need to use an anemometer which measures the wind speed and direction at your exact l ocation. Roughness Roughness relates to the friction played out by uneven ground on the wind. In general a greater level of roughness will slow down the wind speeds more. Smooth surfaces such as water, concrete or tarmac will have little impact, whereas long grass, buildings , hedges and trees are all important factors to consider when sitting your turbine as they can greatly reduce the speed of the wind. These factors also increase turbulence which again reduces wind speeds. Roughness is defined by class; smooth su rfaces have a low roughness class such as concrete runways are 0.5, while landscapes with many trees and buildings have a high roughness class of 3 to 4. To calculate the projected wind speeds at different heights above the ground, roughness length, or the height ab ove ground level where the wind speed is theoretically zero, is used. Wind shear Wind shear shows the relationship between wind speed and height above ground. The graph below shows that wind speed is slower nearer the ground . As the height increases and the surface friction influence lowers, the speed increases logarithmically. 5 The natural logarithmic function this graph is based on is: V = V ref ln (Z / Z o ) / ln (Z ref / Z o) Where V is the wind speed at a certain height Z, V ref , is the known speed at height Z ref , and Z o is the roughness length. Obstacles It is very important to look for potential obstacles to your wind turbine such as buildings and trees - the speed is reduced as the wind swirls around the obstacle, creating turbulence. The porosity of the obstacle must also be considered, for instance trees in winter are fairly open and will still let some wind through, however buildings are solid and so will completely block the wind creating wind shade behind the obstacle. Porosity is defined as the open area divided by the total area of the object facing the wind Wind shade causes a loss of energy due to a slow down effect. This is more pronounced closer to the object and near the bottom, and increases with height and size of the object. Any obstacles should be taken into account if they are within 1km of the potential turbine site. E.g. a building 20 metres tall will cast a shadow that encompasses a full size turbine with a hub height of 50 metres, 300 metres away. So the further away you place your turbine from any obstacle the lower the impact on the wind speed. Prevailing wind direction Winds for a specific site will generally from come from one direction for the majority of the time. This is called the prevailing wind. General rule for prevailing wind speed directions are: Latitude 90 -60 oN 60 -30 oN 30 -0oN 0-30 oS 30 -60 oS 60 -90 oS Direction NE SW NE SE NW SE Other local factors Sea breezes are caused by the land mass heating more quickly than the sun, as the warm air rises it flows out to sea, creating an area of low pressure on land which draws in the cooler sea air. This will potentially alter the prevailing wind direction. During the night as land temperatures decrease the effect is reversed, although these land breezes are much weaker. Factors that can increase the wind speed The tunnel effect is the increase in wind speed between two buildings or hills due to the increase in air pressure as the air is compressed between the obstacles to the wind.