pendence, since deregulation obviously does not always lead to an abundant and reliable supply. As with PV panels, small wind power units can provide renewable energy at a relatively low price. Lagerwey the Windmaster have developed a 5-meter diameter wind turbine for use in urban areas, designed to supply energy to individual grid connected households. So far, 200 have been purchased by the Dutch utility company, NUON, and !here has also been demand from Japan. Henk Lagerweij commented: You see the wind turbine moving away from people, across the farmland towards sea. We can change that.' Delft University of Technology in the Netherlands, supports the idea of small decentralized wind turbines in built-up areas, but believes !hat the first installations will be in industrial areas or office parks, mainly because they generally have less strict building regulations. Once silen!, reliable, low-maintenance wind turbines, that are as easy to install as a PV panel, become available for individual households, !hen a huger consumer market can be opened up. ■ ünce silent, reliable, low-maintenance wind turbines, that are as easy to install as a PV panel, become available far individual households, then a huger consumer market can be opened up. ■ State of the art in small wind turbines Currently, a number of small wind energy converters of several basic types are available for electrical energy production. in !his article we focus on products under kW peak power output. Most of the small systems have a direct drive permanent magnet generator (neodynium, ferrite). Transmissions do not only dissipate energy, but they require maintenance and create noise therefore, they are not preferred in small wind turbines. Other design choices reflect the need for simplicity and low cost as well: wind vanes are used for wind orientation rather than more - T T a n b l l C c 1. Sınai! wiııd turbinc rc:ıtures Status Rcm:ırks Somc c:rnnınlcs HUpowrizinodıı,tlail axis ft largc scrics. provcn product Widcly uscd, mainly in opcıı liclds !nelin, Acrocr:ıft, Bcrgcy, Lagcrwcy, SWoiuntdhıwowcscırW. indnowcr IX)\mwind provcn product M:ıinly in smallcr powcr rangcs. also Provcn opcn fıclds; buildi ng inıcg,ration cxaınplc Vcrılcaluis Savoni us, drag provcn producı Gcncrnlly vcry sikııı and rcliable, stonn Wiııdsidc, Shicld's Jaspira rcsisı:ını, yet l ow cfficicııcy nırbinc [Gtil ) Darricus, lift small scrics Sc\'cral subtyp cs cxisı. oftcn as prototypcs, simplc c onsırnction. foir cflic-icncy; noisc and vibratio ns stili ıo be covcrcd C ombincd lifi proıoıypcs Simplc consırucıion, 110 cxıcm:ı l st:ırt up nccdcdG!obuan. Solavcııt al .ı.ıadı ı gdcr aı • urbines small serics 1.-0w ııoisc, rcliable AES - 621 ECOGENERATION WORLD complex yawing systems. A range of sometimes very innovative braking systems and speed regulation mechanisms can be found as well. Some horizontal axis types tip over backwards in hard winds in a so-called 'helicopter mode'. SToh eu racier :sWtrei nadmh i npdaettre, rSn tai crhotui nngd Bbouui lwd i nregsse. arch The electrical output of systems under 2 kW is often 24 or 48 volts, the aim being battery loading rather than grid connection. Over that size we find also grid-connected systems. The basic differences are in the driving principle and in the orientation of the rotor axis. The driving principle of small wind turbines is either drag or lift. Lift propellers are much more common and have a much higher energy efficiency (up to a theoretical 59%) !han drag turbines (efficiency up to 15%). Horizontal axis wind turbines are by far the most common types; vertical axis types are found less often. The Darrieus turbine is one type of vertical axis turbine !hat cannot start turning by itself - it needs to be started either by another wind turbine (a small Savonius, for example) or by an electric motor. --- Table 2. Adv:ınt:lf! Hori7 ntal axis CS and disadvaıııaecs of axis oricntation in sınall wind turbincs ..o Advantaecs Disad,•antacres • High yicld • subject ıo fatiguc • Well known tcchnology and producı • high mast rcquircd •• LAaurtgocnısaeıri cicsst,alrotw-upcost cnginccring A V d cr v l a ic ıı a ta l g a c x s is Oisadvantages • Not sensitive to changcs in wind direction • strong dynamical load on bladcs and hingcs • Less sensitivc to turbulence • requircs extcrnal start up I • cGoennscı rr ua tcot iro inn, be oa st tiol yn ıpol afcteudr boi nn eb: usitladbi nl eg a n d l i g h t w c i g h t There are a number of reasons for looking at vertical axis turbines for application in built-up environments, despite some inherent disadvantages of the type. The relatively low sensitivity to turbulence. and wind changes and the low weight relative to the power output, make the vertical axis turbine a good candidate for urban turbines. The position of the generator below the rotor rather than behind it offers advantages in roof mounting and service access and requires a much smaller mast. The vertical axis turbine also offers betler possibilities for attractive visual designs, in which the visual impact ofa moving object on the immediate surroundings is minimized. Needless to say, the horizontal axis turbine is stili in the lead, with many well-engineered designs, proven performance and relatively low prices. The number of suitable, commercial vertical axis turbines is yery limited at the moment, but we expect new designs to emerge onto the market in one or two years. Socio-economic acceptance The integration of wind energy converters into the built environ-
RkJQdWJsaXNoZXIy MTcyMTY=