The small wind industry worldwide lacks an essential best practice guide, and in order to create one it is essential to bring together the right tools and, in some cases, to create new ones.
Wind mapping is a very useful tool that provides an indication of what might be possible when it comes to successfully erecting small wind turbines. What might look poor from one point 100 metres away, may look better with a positive wind mapping assessment.
Good dedicated wind turbine design is incremental from the start, but manufacturers of small wind turbines - whether of horizontal axis or vertical axis - with their fingers on the button are hard to find in the marketplace at this moment in time.
A study conducted for Tesco in the UK found that current management of store sites and other buildings where urban wind turbines were to be of benefit lacked any coherent policy. In all cases that could be verified, it was clear that local energy managers had made a choice of a wind turbine without any assessment of local wind speeds, mounting heights and the particular factors of climatic and urban architectural influences on the site.
It is clear that a sales pitch and catalogue blurb took precedence over expert technical analysis. Case studies and commentary from Europe and the US illustrate that this attitude is currently epidemic in the emerging small wind energy industry, and among end users.
For example, on the site of a store in Newton Aycliffe, Durham, Northeast England, a Llumarlite Wind Rotor (also known as WRE and Ropatec) was used instead of a HAWT because it was quieter in operation – a good reason. However, the wind turbine’s viability suffered because the machine was installed in a car park at just 6 m above the ground.
This made the installation unsatisfactory with regard to best results. The reason given for this was that other decision makers had asked for a wind turbine to be installed quickly and "off-the-shelf". But if the wind turbine had been installed well above the roof line of the store and surrounding buildings, a better capacity result would have been obtained.
Had a full scale design appraisal been made, then a totally different solution would have resulted, either using a vertical axis machine of a larger capacity or solar technologies - whether roof mounted solar photovoltaic (PV) panels, roofs covered with solar PV skins or Interseasonal Heat Transfer (IHT) systems and thermal bank storage.
In a number of cases, the buildings studied as part of the report were to be fitted with micro-generation wind turbines of minimal power. In particular, the use of multiple small wind turbines that sit like a line of desk-fans along a parapet - with capacities of 1 kW. As a way to give the company a 'green image', there may be a public relations case, but as a contribution to reducing energy consumption and energy costs on a realistic and pragmatic scale, then such fantasy solutions are not sustainable and do nothing to meet any forecast to reduce climate change emissions.
One major proposal was to set up a specialist in-house working party to produce a Best Practice Guide. This working party would consist of senior technical managers, senior engineers and specialist consultants, with input from the R&D departments of universities specialising in the particular field, and including an independent chairmanship.
To date nothing has happened. Had such a working party been convened, the need to produce a coherent and usable tool would have soon become apparent and, using current knowledge of wind speeds and other factors related to urban densities and terrain roughness, may well have led to a totally different approach to reducing energy use.
The certification issue
Certification, coupled with a good practice guide that includes the nuts and bolts of how to go about installing a wind turbine and whether it is worth doing, has become a hot issue in the emerging small wind turbine industry.
There are murmurs on this emanating from the Netherlands, the UK and the US that various institutions, universities and pragmatic manufacturers - such as Turby (NL), Vertical Wind Energy Ltd (UK) and Mariah Power (US) - are seeking to create pro-active certification.
But why haven't bodies such as the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), the Chartered Institution of Building Services Engineers (IBSE), the Carbon Trust and the British Wind Energy Association (BWEA) not made the decision to join forces with companies like Vertical Wind Energy, which believes that some form of pre-certification is essential to build a viable professional industry, especially during these years of quiet investment. Certainly specialist wind consultants, such as Engenuity Ltd, regard this concept as a market leader from a yield-cost perspective.
Such a certification should become a single wind industry standard for multiple countries and geographical regions. This approach is challenging and would include different guidelines for wind turbines operating in the urban built environment compared to those operating in an open field. However, there are so many aspects to locations across the world that each nation and its sub-climatic and geographical zones, all with different constraints and variables, would need good practice design guides that suit the different regions.
It has become clear that there is a need for company purchasing agents to appreciate the differences between different types of wind turbine rotors. For example, vertical axis-type small-wind Darrieus rotors are generally not self-starting. With high degrees of turbulence, typically 30% and upwards, continuous start-ups can easily add up to hundreds of kilowatt-hours consumed, with no gain to the client.
Whilst most turbulence studies are undertaken on horizontal axial wind turbines, this happens less so on vertical axial machines in which vector components of turbulence interact differently.
Planning tool – ECHOES
Echoes stands for Environmentally Controlled Human Operational Enclosed/External Space.
It is a planning tool based upon the factors influencing a specific building site, when both natural and man-made impacts are taken into account. The tool is interfaced to assess the particular needs (both externally and internally) of any built structure, to create the best possible environmental and ecological conditions in a commonsense way.
Factors - spatial/luminous/sonic/thermal/matter and energy, then all correlated to man’s environmental relations, passive and active controls;
Factors influencing any site location need to be taken into account before any architectural design is undertaken;
An external meso- and micro-assessment such as solar, wind, rain and air quality, including radiation, noise and other aspects of a surrounding envelope, is critical.
ECHOES can be an important item in the toolbox of a Best Practice Guide for any assessment of the use of an urban wind turbine.
As part of any methodology of design, all the climatic and geographical factors influencing any site location must be taken into account. In 1970 I proposed such a methodology, in which any building site location should first be fully assessed by all the influencing factors. These include wind, rain, solar and electro-magnetic force fields, as well as the impact of other natural forces such as man-made pollution, noise, and interface with other buildings. Known as Environmentally Controlled Human Operational External-Internal Space (ECHOES), I have used this method with beneficial results on hundreds of projects.
This method of working allowed for a careful assessment of costs and returns, both financial and environmental, at every stage of design. It is a tool that allows for even greater interface of different disciplines, essential to all construction and environmental planning (see box – Environmentally Controlled Human Operational Enclosed/External Space (E C H O E S).
A new direction
Not surprisingly, the Tesco study concluded that bad news stories are not good for business, even if they include a little spin. The problem is not the wind turbine but the wind. Small wind needs a new direction.
Doubling the rotor radius increases wind power four times over. Doubling wind speed increases wind power eight times. At an average wind speed of 7 metres per second (m/s), a wind turbine can deliver 5.36 times more energy than an average wind speed of four m/s.
A number of premier manufacturers fully recognise the need to produce wind turbines for an urban environment that can be mounted high where wind blows at its optimum. These are quiet, high in performance at affordable costs, and resilient to damage from high wind gusts.
However, Steven Peace, technical director of the British-Irish company Vertical Wind Energy Ltd, believes that a far better indication of a machine’s performance is its annual yield. Vertical Wind Energy are using the current period of a slow economic climate to develop a proprietary programme which runs on CFD software to stimulate with extreme accuracy the flows and velocities of wind around buildings, roofs, trees, and other structures.
By inputting topographic data (building shapes and dimensions) and wind speed information on line from Google Earth and met office sites, drawings and pictures are generated that depict the wind flow lines around a structure. Coloured lines indicate flow velocities.
The optimum location of wind turbines placed at the correct height in the highest velocity wind flow can yield an extra 25%. Peace is a firm advocate that the best position for any wind turbine would be on the top of a hill in open countryside. And he argues that whilst there are urban wind turbines which are quiet, without flicker and vibration, that can become part of an architectural landscape, many in the current marketplace simply produce negative returns and are not fit for purpose. It would prove beneficial if all manufacturers would give capacity outputs in simple terms, such as kilowatt hours per day (kWh/d).
As physics professor David MacKay explains in his 'must-read' book about tackling our energy needs, Sustainable Energy-Without The Hot Air, published by UIT, “we know that one 40 W lightbulb, kept switched on all day, uses one kWh per day. Bringing all our needs down to a common denominator will help us focus and sharpen the debate on the bigger energy needs.”
Current limitations and forecasting
How much power can commercial small wind turbines generate?
|Applications||Power Rating (Watts)|
|Old light bulb||60|
|Low energy bulb||20|
|1 bar electric fire||1000|
Looking at the box in this article showing the typical power consumption of normal household appliances illustrates the current limitation in regard to the power capacity and beneficial use of many small wind turbines.
For the industry to take on a greater role in making use of the excellent wind regimes that exist across most of southern Ireland, virtually all of England and the eastern coastal regime of Europe from Brittany to Denmark and into Scandinavia, small wind needs a new direction. And to this end, the development of embedded wind generators within high building structures is an intelligent way to progress.
Wind power forecasts have become a necessary input to the daily management of wind generation, whether for large scale wind farms or for small scale urban machines. Extensive research by the Technical University of Denmark has resulted in the creation of real-time forecasts for different wind regimes. These can change depending on highly-variable meteorological conditions, which themselves can radically change as the impact of global climate change factors are added to the equation. A more global view of wind power forecasting and decision-problems will benefit both forecasters and forecast users.
Forecasting is a global problem. It encompasses meteorological, mathematical, power system and economic aspects which need to be considered in a cross-disciplinary fashion. It is an important tool that will need to be continually updated in the same way as the personal computer reminds us to do. The environmentally friendliness of wind energy has its costs; those of variability and uncertainty, which with the right tools can be accommodated.
The creation of wind turbines and solar wind sails, as well as the use of solar and wind walls, incremental with the building, and other devices to capture the free but changeable energy of wind across the world, is required – and is within reach. In tall buildings the ecology of the sky is the key.
For example, in the 71 story Pearl River Tower now being built in Guangzhou, China, four wind turbines will be incorporated into the structure. The building has been designed to drive air through cavities to generate one million kWh of electricity per year. Skidmore, Owings & Merrill, the US architects, had also considered the introduction of micro-turbines. Sadly, this proposal was dropped after opposition from the local utility company, which had reservations about rival sources of power generation.
Vertical wind turbines should become an incremental element of motorways in places with a good wind regime. Such machines, running along the centre safety zones of prefabricated motorways (that are themselves solar collectors) combined with PV barrier panels, could transform transport routes into ribbons of non-polluting energy for cooling and warming buildings. And providing non-toxic, non-carbon energy for a new form of non-toxic, zero-carbon transport.
But that’s another story!
Approximate power and equivalents
Wind speed 4.5 m/s
|Windsave, Ampair and similar||20-40 W||= 2 x low energy lamps|
|Proven, VWE, Turby + similar||100-200 W||= TV and 4 x low lamps|
5.5 m/s (UK average)
|Windsave, Ampair, etc.||100-150 W||= 5 low energy lamps, TV plus one low lamp|
|Proven, VWE, Turby, etc.||300-500 W||= 1 or 2 TVs + fridge|
|Windsave, Ampair, etc.||400-600 W||= 2 TVs + fridge|
|Proven, VWE, Turby, etc.||1000-1500 W||= 1 bar electric fire, TV + fridge|
|Windsave, Ampair and similar||1000 W||= 1 bar electric fire + TV|
|Proven, VWE, Turby, etc.||2000-3000 W||= 2 bar electric fire, PV + fridge|
These figures have been collated from the current range of manufacturers. They prove that the height of any small urban wind turbine is important. Also that solar PV can produce better results for housing.
It is because of figures like these that manufacturers of vertical wind turbines, such as Turby and VWE, are restricting their installations to commercial applications on high rise buildings and industry.
About the author:
Bill Holdsworth is an independent consultant in the field of environmental and energy engineering and adaptive climate technology.
Duing his years as design consultant, he has worked on projects worldwide that have included theatres, concert halls, hospitals, sports centres, schools, university buildings, offices and housing and early district heating systems. Innovative design work included wind and solar engineering as well as interseasonal heat energy storage, which has taken more than 40 years to become accepted. He has also advised on sustainable strategies for the City of Zagreb, Fresno-California and Istanbul. In the past 12 years, he has worked on research projects with teh University of Kinston-upon-Thames, UK, and with London Metropolitan University.
He is currently enganged by the UK based international sumernarjet chaing Tesco to develop new energy policies and technologies to enable the company to improve their response to climate impacts and global warming. His first undertaking was an in-depth study of urban wind turbines that is summarised in this series of articles.
Tel: +31 24 388 08 66