The increased focus on reducing

Turan, Peacock... 4/07/07 10:38 Page 1 Volume 3 - Number 3 - May 2007 (106-110) Abstract The increased focus on reducing the CO 2 emissions attributable to buildings has stimulated small scale, low carbon, electricity generating techlogies designed to meet some or part of local demand. Among these techlogies, small scale wind turbines appear to be promising. Aided by policy stimulation, some established manufacturers are expanding into this market and several new manufacturers and techlogies are at various stages of market entry. However, many significant issues remain unaddressed, for instance: planning procedure, structural, vibration and safety issues in the case of a roof mounted application, wind regime analysis and energy yield estimate of turbines in the Micro and Small Wind Turbine Applications in the Built Environment Seyhan Turan, A.D. Peacock and M. Newborough Energy Academy, Heriot-Watt University, Edinburgh, UK, EH14 4A built environment, and the effects of such devices on the electricity distribution system. This study investigates micro and small wind turbine techlogies and their applicability to the built environment as described by a number of case studies. State of the art techlogies, procedures for estimating energy yield, and major factors affecting the energy yield are examined. The applicability of various techlogies across the UK building stock is studied. Some site specific examples are given to highlight the implications of various factors from both single and multiple scale energy generation. Keywords : small and micro wind turbines, building integrated, micro generation, capacity factor, wind characteristics. 1. Introduction Building integrated micro generation techlogies are increasingly being explored to generate energy on-site and reduce CO 2 emissions. A number of different techlogies are contributing to this emerging market, among them small and micro wind turbines (MWT). There are around 700 MWT installations in the UK with approximately 100 of them are in the urban environment [1]. The majority of these have been installed for educational reasons (at schools or environment centres), very few are domestic systems, and only 16% of the total is in the most built-up areas [2]. Installations are dominated by Horizontal Axis Wind Turbines and they are mostly established techlogies (e.g. Proven and Gazelle). However there is a movement in the small wind turbine industry towards the urban environment market, rooftop installations (e.g. Eclectic Energy, Renewable Devices, Windsave), and towards Vertical Axis Wind Turbines (e.g. Rugged Renewables, XCO2). These techlogies are generating positive interest from both public and private sectors. This study forms part of the Carbon Trust/EPSRC funded Carbon Vision project called TARBASE which aims to identify methods for reducing CO 2 emissions from existing UK building stock by 50% by 2030. Investigating the carbon saving potential of MWT and their applicability to existing buildings is one of the project objectives. 2. Methodology 2.1. Selecting the turbine At the outset, a number of issues concerning deployment of MWT in the built environment were considered. These include a) compliance with all health and safety requirements (both structural and electrical), b) planning permission, c) ise levels, d) reliable operation, e) ecomics, f) payback times and g) visual intrusion. Beyond assessment of these essential measures, determining suitability and compatibility of turbine techlogies across the UK building stock is a n trivial task and is dependant on various interrelated factors. Several established and emerging MWT techlogies were examined in detail with respect to specific buildings, project objectives and boundaries. The major factors affecting the applicability of MWT include; a) wind and turbine characteristics, b) building features, c) surrounding environment and d) legislative measures. Following an extensive review, 16 MWT models were selected for assessment of suitability. These turbines are broadly classified as micro, small, medium, and large appli- 106

Turan, Peacock... 4/07/07 10:38 Page 2 cations according to turbine capacity. Building variant characteristics relating to MWT applicability were examined thoroughly allowing suitable turbine models to be defined. A number of tech-ecomic barriers to expansion of the MWT market exist in the UK: a) Unlike the PV industry, agreement or standard on the technical specifications of MWT exists. Therefore different rated wind speeds, energy yield estimates, and safety measures for different conditions are used by manufacturers making it difficult to compare turbine performance [3]. b) No specific guidelines for planning permission applications exist. Although Planning Policy Statement 22 encourages renewable energy applications, it does t include small scale generation and micro-wind. Lack of guidelines compounded by authorities lack of experience results in confusion and this leads to difficulties in planning permission applications [1]. c) Although grid connection of small wind systems is simplified by G83/1 regulations, complications remain in metering in the case of exported electricity [4]. The implication of large levels of generation from micro-wind on the Electricity Supply Industry is t kwn. d) Wind characteristics in urban locations differ greatly from those in traditional locations in rural areas. Turbulent flow and lower wind speeds are common wind characteristics of the built environment resulting in a lower energy yield, lower capacity factor (CF) (Table 1), more random patterns of generation, and maintenance and life cycle concerns. Although wind characteristics in the urban environment follow the general patterns of generic wind conditions over a large time period (higher wind speeds and availability in winter followed by less productive summer months) the strength of wind is considerably lower. When considered on a shorter time scale, e.g. a daily or hourly basis it will be more variable, intermittent and turbulent and therefore much less predictable. [5] Turbine siting is fundamental to energy yield and is complicated by; a) land availability (with mast mounted turbines), b) structural and safety issues (with rooftop turbines), c) planning permission, d) ise, and e) visual intrusion. Also, wind characteristics vary considerable even within the vicinity of a site (Table 3). Traditional guidelines of siting a turbine at least a horizontal distance of 10-20 times the vertical height of an obstruction or twice the height above an obstruction is t applicable for many applications in the built environment, since 90% of houses in UK do t comply with these conditions [6]. Regarding these factors rooftop sites appear to be more promising. Furthermore some studies suggest that due to regions of flow above the roof where the velocity of the wind is enhanced rooftop applications can be feasible even in low wind speed environments. However some authors are t in favour of rooftop mounted turbines due to unaddressed concerns of safety, turbulence, and ise [7]. 3. Energy yield analysis The two main variables in determining energy yield are the wind characteristics (in relation to the surrounding environment and building features) and the turbine characteristics. There are several methodologies used by manufacturers for estimating the energy yield of wind turbines. These vary in accuracy and also suitability to the project objectives, when accounting for boundaries and data availability. Several references [8] suggest that the standard methodology of energy yield analysis is t relevant if it is applied in urban or semi-urban conditions where the surrounding environment, wind characteristics and roughness length are very different from traditional wind turbine applications. Furthermore, common use of the NOABL wind database results in large errors since the database does t take into account the above variables for built-up areas (Table 1) [1]. For instance, the energy yield expected from a kw Proven turbine minally installed on the roof of the RIBA headquarters in central London is estimated to be 5918kWh using the NAOBL database. This estimation fell to 1497kWh (a factor of nearly four) when using wind data measured on site. There are two main tasks which were undertaken to analyse the energy yield in this investigation: a) Wind speed analysis: weather stations within the campus of Heriot Watt University on the outskirts of Edinburgh were used as the main source of wind speed information. The stations are situated in two different locations at a height of 2m. Several years of data were available with a temporal resolution of 10 minutes. b) Energy yield calculation methodology: a simple method of calculating energy output on the basis of power curves (provided by manufacturers) was applied for each wind dataset. 4. Case study: Detached house To demonstrate the chosen methodology, the energy yields of a range of suitable turbines for a detached house were estimated. The house was assumed to be of recent construction (1980-1996), to have a pitched roof with slate tiles and be 8 metres high to the roof apex. The building is located in Edinburgh in a common residential area where, it is assumed stringent planning regulations exist. It has an annual electricity demand of 8.6 MWh. 107

Turan, Peacock... 4/07/07 10:38 Page 3 TABLE 1. Energy yield of a Proven kw wind turbine estimated using NAOBL database and measured wind data for 9 different urban sites Site Hub Height measured wind Speed (m/s) estimated wind speed from NOABL (m/s) annual energy yield from measured wind (kwh) annual energy yield from NOABL (kwh) CF using measured wind CF using NOABL Sports-centre, Scotland 9 2.7 4.3 730 2850 3.3 13.0 Primary School, Bucks 9 6.3 2049 6851 9.3 31.3 Eco-Centre, Teeside 30 5.2 4546 6427 20.7 29.3 Reading University Meteorology Department 8 2.8 4.8 823 3759 17.2 Oxford University, Engineering Building 45 1990 6002 9.1 27.4 Rooftop, RIBA building, London 36.5 3.4 1497 5918 6.8 27.0 Tower block, Portland Est.? 8.0 10188 6427 46.5 29.3 Hockerton Housing Project 18 5.0 4147 6002 18.9 27.4 Heriot Watt University 10 2.80 5.1 823 4345 19.8 4.1 Wind turbines Eclectic Energy manufactures a 400W turbine (D400) (Table 2). It is the smallest turbine in the selection and is aimed at small households and rooftop applications. It has an advantage in terms of planning permission, as well as structural and safety considerations. Proven turbines are the most market mature with several turbines having been deployed across the UK (both mast-mounted and rooftop). Swift turbines are more recent entrants into the marketplace, with techlogy aimed specifically at the built environment. They are becoming increasingly popular for aesthetic reasons and low ise levels. 4.2 Calculation Method Two consecutive years (2000 and 2001) at two different weather sites within a mile distance (site A and B at 2m height) at Heriot Watt University were selected for wind data. TABLE 2. Wind turbines considered for the detached dwelling case study Turbine D400 (Eclectic Energy) Swift 1.5 Proven WT 0.6 Proven WT Proven WT 6 Rated power(kw) 0.4 1.5 0.6 6.0 Rotor Diameter 1.1 2.0 3.5 5.5 Suitable for roof mounted for detached house yes yes Site B is surrounded by trees, and therefore sheltered, and A is an exposed site without obstructions to the prevailing wind direction. Both data sets were extrapolated to a height of 10m to match the likely hub height of the installed turbine. Annual mean speed results are higher at site A than site B (Table 3). The proportion of time that the wind speed was below the cut in speed of the micro turbines considered here ranged from 32% to 74% of the year. The electrical demand of the building is provided annually by a data set with a temporal precision of 10 minutes. Power and energy yield is calculated by turbine power curves applied to the wind data sets. Turbines are assumed to have downtime due to maintenance or failure and there aren t any mechanical and electrical losses during operation. 4.3 Results The energy yield varies considerably due to turbine size and the wind characteristics (Table 4). The annual CFs ran- TABLE 3. Wind speed data for the two different sites and years considered Year/Wind site 2000 A 2001 A 2000 B 2001 B Mean wind speed (m/s) 4.3 3.6 2.1 1.7 Proportion of wind speed <3m/s 32.3 43.1 65.1 73.7 108

Turan, Peacock... 4/07/07 10:38 Page 4 ged from 12.3%-18.9% dependant on turbine at the high wind site in 2000, compared to minal CFs assumed for network scale wind turbines of 27% [9]. Year 2000 wind speed results are higher than 2001 resulting in a significant difference in CFs and energy yield of the turbines, for instance the CF of the Swift 1.5kW turbine was 15.2% in 2000 at site A compared to % in 2001. This indicates the scale of annual variation one might expect from wind generation as applied to semi-urban sites. Matching of the electricity demand of the dwelling to the electricity generation was considered for wind site A in year 2000. The electricity generated by the turbine matched only a proportion of the annual electricity demand of the dwelling that ranged from 4.6% to 42.1% for the 400W and 6.0kW turbines respectively. The amount of electricity exported from the dwelling is found to be significant ranging from 8.6% of electricity generated with the 400W turbine to 63.5% with the 6.0kW turbine. The cost savings attributable to micro-wind depend on many factors such as capital costs, government incentives and electricity prices. However, given the amount of electricity exported in the example shown (Figure 1), the value placed on exported electricity by electricity supply companies will have a fundamental bearing on the ecomic veracity of deployment. TABLE 4. Energy yield of the turbines and capacity factors Turbines Rated power(kw) Rotor Diameter Suitable for roof mounted for detached house 431 12.3 D400 177 5.1 0.4W 79 2.3 36 1.1 2001 15.2 Swift 802 1.5kW 331 157 1.2 3725 17.0 Proven 1518 6.9 kw 614 2.8 Proven 259 9951 4139 1.2 18.9 7.9 Figure 1. Electricity exported by the turbine and imported by the house from the high wind site in year 2000. 6.0kW 1705 3.2 704 1.3 5. Conclusions Micro-wind turbines can contribute to reduction on CO 2 emissions of the existing built asset base. Methodologies can be developed that consider a range of factors to ensure the applicability of specific turbines to specific buildings. Estimating the energy yield, however is problematic as a clear eugh understanding of urban wind has yet to be developed that would allow widely applicable general statements to be made. Estimations made using existing databases are inaccurate by as much as a factor of 5 when compared with on-site measurement of wind. It is evident from the case study that capacity factors of turbines will be low and highly variable and a substantial proportion of electricity generated will t be used instantaneously by the discrete dwelling i.e. will be exported to the electricity network. 109

Turan, Peacock... 4/07/07 10:38 Page 5 References [1] Small wind turbines for the urban environment: State of the art, case studies, & ecomic analysis, P.Robinson, Reading University, Energy Group (2005). [2] Investigation into the installation of small wind turbines in an urban environment S. Carroll, Loughborough University, (2005). [3] Choosing a Home-Sized Wind Generator, M. Sagrillo, Home Power, 90 August/September (2002). [4] Small scale, building integrated, wind power systems E. Dayan, BRE September (2005). [5] Tarbase Project, small wind report - in progress, S.Turan (2006). [6] Can we harvest useful wind energy from the roofs of our buildings? N. Martin, Building for a future, 15(3) (2005). [7]http://www.wind-works.org/articles/RoofTopMounting.htmlBWEA, P. Gipe, December, (2005). [8] Personal communications, Dr T. Cockerill, Reading University, Energy Group, January, (2006). [9] Wind power and the UK wind resource Environmental Change Institute (2005). 110