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Getting real about small wind
Feature article
Getting real about small wind PART 4: IN THE FINAL PART OF A SERIES OF SPECIAL ARTICLES ABOUT THE SMALL WIND INDUSTRY FOR RENEWABLE ENERGY FOCUS, WIND ENERGY EXPERT DAVID SHARMAN TURNS HIS ATTENTION TO THE USERS AND THE INSTALLERS OF EQUIPMENT.
Until now the small wind industry has focussed on making good quality wind turbines. Although this is still a work in progress the next major challenge is how to handle very large numbers of installations.
The products themselves can be adapted to make them easier to install by people with less experience – this is a normal industrial problem and will be overcome in the normal industrial manner. But what isn’t normal is the challenge of predicting the wind resource at a myriad of different small wind sites, in a cost-effective and reliable way. This was one of the major talking points at the second International Small Wind Conference (ISWC) run by the RenewableUK (formerly BWEA). The ISWC conference and exhibition is now the largest dedicated small wind gathering in the world, with over 800 delegates and 40 exhibitors from 20 countries.
Performance prediction issues Even when the turbine power curves are known with confidence, predicting the power output of a turbine at a given location can be difficult, especially if the clients are in a hurry. Just as with large wind turbines the ideal way of predicting performance at a particular site is to install an anemometer for at least a full year, and have the data processed by an independent site assessment specialist. This allows the results to be correlated with other longerterm data to give a performance prediction that is accurate to within 5-15%. But typically such a study will cost approximately £5000, and it does require patience. For this reason it is not common to see independent studies commissioned for wind turbines of less than 20 kW or so. However, the well-respected North American Board of Certified Energy Practitioners (NABCEP) is currently finalising the syllabus and examinations for what will be the first fully-trained group of truly independent certified small wind site assessors. Having such an independent site assessment report can be a precondition of obtaining financing for the more expensive small wind turbines. The PowerPredictor is a very cost-effective combined datalogger and anemometer.
38
renewable energy focus
At the other end of the scale for turbines of less than 1 kW, it is not normally cost-effective to engage an independent assessor. Instead a DIY owner will examine the site and make a near-instant decision. This may be assisted by online wind atlases or wind prediction databases, but at the moment these are error prone – so much so that local experience is likely to be of greater benefit.
May/June 2010
Wind/small wind
And in between these two extremes the installer will normally conduct a basic site assessment, perhaps assisted by short-duration anemometry. To a certain extent there is a conflict of interest between the desire of the installer to make a sale – and give realistic, but perhaps depressingly low and realistic, performance predictions. For this reason, the UK’s Microgeneration Certification Scheme (MCS) requires installers to give a site and turbine-specific performance estimate using a specified performance prediction methodology. MCS installers are allowed to offer other predictions but they must always give this basic prediction so that consumers can compare offers on a common basis.
Zephyr AirDolphin turbines being trialled in urban England.
With respect to performance prediction the requirements to become an MCS-certified installer are not yet as onerous as those for NABCEP, but it is expected that MCS will evolve over the coming years. In addition, through the Renewable Energy Assurance Ltd (REAL) assurance scheme there is a consumer code of practice that all MCS installers must comply with.
Anemometers and data loggers One of the main costs of an independent site assessment is the cost and complexity of the anemometer, the data logger, and the anemometer mast. A number of companies have entered this market with consumerready equipment, which seeks to drive down the costs as well as demystify the process. The most notable offering is the PowerPredictor from Better Generation in the UK. For £100 the company sells a basic data logger and anemometer which an enthusiast can self-install. Using this device, data from a site can be uploaded via the internet to Better Generation’s website where the results are presented in a standardised format – along with recommendations as to the suitability of the site for different wind turbines or solar panels.
Clearly this poses a threat to turbine manufacturers and installers, as it places an independent ‘intermediary’ between them and a pool of qualified clients.
Even when the turbine power curves are known with confidence, predicting the power output of a turbine at a given location can be difficult, especially if the clients are in a hurry. Another commercial data logger is from Logic Energy in Scotland, which costs around £200 – including the anemometer. The equipment is higher resolution than that of the PowerPredictor, but it is not as easy for the novice to analyse the results and as a consequence tends to be used by installers and site assessors (or by schools rather than by individual clients). There are a number of similar American products including those from APRS World in Minnesota, which designs and manufactures a wide range of data logger and anemometer products. Some wind turbines are starting to sport their own data loggers, notably the Ampair 6000 and the Quiet Revolution QR5. Whilst it may seem a bit late to measure the wind resource after installation, the patient accumulation of data does allow a picture to be built up of real wind speeds across the world that will be of value to other prospective clients. For this reason internet-enabled devices are likely to become prevalent over the next few years, with built-in mobile telephones to transmit the data to manufacturers, intermediaries, and consumers.
The US Department of Energy (DoE) project aims to build upon the best of the available resource estimators such as these from Cadmus, Encraft, and the Californian SWEET estimator.
Critics of the very cheap PowerPredictor units say that they are not as precise or calibrated. Supporters point out that given the natural annual variation in wind resource at a site, it is not appropriate to over-invest in high precision equipment. Perhaps the biggest advantage of the Power-
renewable energy focus
May/June 2010
39
Wind/small wind
as those proposed by the Carbon Trust. Given that the Carbon Trust is dependent on a proprietary wind atlas and terrain type atlas, this is encouraging news for those who are trying to avoid proprietary lock-in. Looking to the future the industry needs to improve these terrain correction factors further, as otherwise clients will be forced to put up anemometer masts for a year just as they would with a large wind turbine. The US Department of Energy (DoE) is funding an improved wind resource prediction project – Analysis Tool for Distributed Wind Technologies – which comprises a transatlantic consortium with access to much of the UK trial experience – as well as some similar studies in the USA. The team is coordinated by the Cadmus Group of Massachusetts along with the California Wind Energy Cooperative; and has Encraft as the UK coordinator with further UK contributions from Loughborough University, BRE, Ampair and Quiet Revolution. It is hoped that this will result in a globally applicable public domain tool for more accurate prediction.
CFD models Developers of large wind farms invest in computational fluid dynamics (CFD) models such as WASP and WindSim to assess the influence of terrain features and wake effects from other turbines. Conceptually these are no different from the situation faced by small wind turbine owners, albeit that the small wind turbine owner is in a more complex situation – and with less money to spend. In the UK both the BRE and Lougborough University have conducted CFD analyses of various typical individual buildings (and aggregated buildings). These have been validated against wind tunnel testing by both organisations, and the results have been published. Some of them are included within the EST reports and others in academic proceedings.
The smallest units such as this Rutland do not need a site survey with an anemometer before installation.
Predictor approach is that it automates the knowledge-intensive task of data processing, and gives a standardised report at zero cost.
Wind atlases & wind models The existing publicly available wind atlases and wind models are crude. In the UK the publicly available wind atlas (known as NOABL) does not account for terrain types, and so within the installer assessment side of the MCS certification scheme a set of terrain correction factors has been introduced – based upon work carried out by the Building Research Establishment (BRE). The EST trial (a report on the first-ever comprehensive monitoring programme of domestic small scale wind turbines in the UK) suggested that these go a long way towards reducing uncertainty. Further work was presented by Ben Cosh of The Green Company at ISWC 2010, which suggests that these MCS correction factors are at least as good
40
renewable energy focus
May/June 2010
In France and Portugal further work has been carried out by INETI Institute of the Portugese Department of Renewable Energy working in conjunction with the commercial company Meteodyn, which has a commercially available CFD tool, MeteoDyn. INETI is proposing that commercial costs are overcome by running CFD models for all urban areas, and making the results publicly available. There are also research projects under discussion in Spain and USA with CIEMAT and NREL which would look to validate CFD models against full-size buildings that are shaped to enhance windflow. Some other academic institutions around the world have indicated similar interests, including CSTB of France.
Financial advice Installers are rightly pointing out that there is no conceptual difference between selling a pension and selling a wind turbine. In both cases a product costing US$20,000-US$100,000 will yield an annual income of US$2000-US$10,000. In most countries financial advisors are regulated and must be insured so that clients can obtain redress if the financial product does not perform as advertised. Even though a small wind turbine can be sold on the second hand market if the site is not suitable, it is
Wind/small wind
to be expected that over the next few years the installer community will be pressured to give financial performance guarantees. They will therefore be seeking solutions from manufacturers and academics to manage this risk.
Installers are rightly pointing out that there is no conceptual difference between selling a pension and selling a wind turbine. In both cases a product costing US$20,000-US$100,000 will yield an annual income of US$2000-US$10,000. Conclusion Site evaluation remains an art, and for the time being the consumer must either accept this or invest in the time and money required to conduct a full wind monitoring campaign (and associated analysis) for at least one year. If complex CFD simulations are appropriate there are now commercial consultancies which are able to perform them. Consumers need to make an assessment of whether these are cost effective for their project. And if they don’t have the patience to perform cheap data logging using a £100 device, they cannot hold either the manufacturer or installer responsible. Over the next couple of years it is likely that progress will be made regarding site resource evaluation as a result of the broad campaign being taken forward around the world. In the meantime, one should be cautious about unknown independent consultants who assemble marketing literature and internet quotes and deploy them out of context – to the detriment of the small wind industry. Trusted independent experts include Paul Gipe, Mick Sagrillo, Ian Woofend, and Hugh Piggott. And increasingly even these gurus cannot keep track of the many advances that are being made, so the formal committee structures of the American Wind Energy Association (AWEA) and RenewableUK are a vital resource, if the industry is to achieve effective coordination of its endeavours.
About the author: David Sharman is managing director of the UK wind turbine manufacturer Ampair. He serves on a number of small wind turbine committees including the international IEC and IEA committees; the USA NEC committee; and the UK committees of the MCS and RenewableUK. He is a systems engineer with a BEng (Hons) from RNEC Manadon and an MSc from MIT. Prior to Ampair he was an officer in the Royal Navy, and an operations and project manager in Shell. He has lived and worked in many countries around the world including several years in Latin America. This article expresses his personal views.
renewable energy focus
May/June 2010
41
Getting real about small wind PART 4: IN THE FINAL PART OF A SERIES OF SPECIAL ARTICLES ABOUT THE SMALL WIND INDUSTRY FOR RENEWABLE ENERGY FOCUS, WIND ENERGY EXPERT DAVID SHARMAN TURNS HIS ATTENTION TO THE USERS AND THE INSTALLERS OF EQUIPMENT.
Until now the small wind industry has focussed on making good quality wind turbines. Although this is still a work in progress the next major challenge is how to handle very large numbers of installations.
The products themselves can be adapted to make them easier to install by people with less experience – this is a normal industrial problem and will be overcome in the normal industrial manner. But what isn’t normal is the challenge of predicting the wind resource at a myriad of different small wind sites, in a cost-effective and reliable way. This was one of the major talking points at the second International Small Wind Conference (ISWC) run by the RenewableUK (formerly BWEA). The ISWC conference and exhibition is now the largest dedicated small wind gathering in the world, with over 800 delegates and 40 exhibitors from 20 countries.
Performance prediction issues Even when the turbine power curves are known with confidence, predicting the power output of a turbine at a given location can be difficult, especially if the clients are in a hurry. Just as with large wind turbines the ideal way of predicting performance at a particular site is to install an anemometer for at least a full year, and have the data processed by an independent site assessment specialist. This allows the results to be correlated with other longerterm data to give a performance prediction that is accurate to within 5-15%. But typically such a study will cost approximately £5000, and it does require patience. For this reason it is not common to see independent studies commissioned for wind turbines of less than 20 kW or so. However, the well-respected North American Board of Certified Energy Practitioners (NABCEP) is currently finalising the syllabus and examinations for what will be the first fully-trained group of truly independent certified small wind site assessors. Having such an independent site assessment report can be a precondition of obtaining financing for the more expensive small wind turbines. The PowerPredictor is a very cost-effective combined datalogger and anemometer.
38
renewable energy focus
At the other end of the scale for turbines of less than 1 kW, it is not normally cost-effective to engage an independent assessor. Instead a DIY owner will examine the site and make a near-instant decision. This may be assisted by online wind atlases or wind prediction databases, but at the moment these are error prone – so much so that local experience is likely to be of greater benefit.
May/June 2010
Wind/small wind
And in between these two extremes the installer will normally conduct a basic site assessment, perhaps assisted by short-duration anemometry. To a certain extent there is a conflict of interest between the desire of the installer to make a sale – and give realistic, but perhaps depressingly low and realistic, performance predictions. For this reason, the UK’s Microgeneration Certification Scheme (MCS) requires installers to give a site and turbine-specific performance estimate using a specified performance prediction methodology. MCS installers are allowed to offer other predictions but they must always give this basic prediction so that consumers can compare offers on a common basis.
Zephyr AirDolphin turbines being trialled in urban England.
With respect to performance prediction the requirements to become an MCS-certified installer are not yet as onerous as those for NABCEP, but it is expected that MCS will evolve over the coming years. In addition, through the Renewable Energy Assurance Ltd (REAL) assurance scheme there is a consumer code of practice that all MCS installers must comply with.
Anemometers and data loggers One of the main costs of an independent site assessment is the cost and complexity of the anemometer, the data logger, and the anemometer mast. A number of companies have entered this market with consumerready equipment, which seeks to drive down the costs as well as demystify the process. The most notable offering is the PowerPredictor from Better Generation in the UK. For £100 the company sells a basic data logger and anemometer which an enthusiast can self-install. Using this device, data from a site can be uploaded via the internet to Better Generation’s website where the results are presented in a standardised format – along with recommendations as to the suitability of the site for different wind turbines or solar panels.
Clearly this poses a threat to turbine manufacturers and installers, as it places an independent ‘intermediary’ between them and a pool of qualified clients.
Even when the turbine power curves are known with confidence, predicting the power output of a turbine at a given location can be difficult, especially if the clients are in a hurry. Another commercial data logger is from Logic Energy in Scotland, which costs around £200 – including the anemometer. The equipment is higher resolution than that of the PowerPredictor, but it is not as easy for the novice to analyse the results and as a consequence tends to be used by installers and site assessors (or by schools rather than by individual clients). There are a number of similar American products including those from APRS World in Minnesota, which designs and manufactures a wide range of data logger and anemometer products. Some wind turbines are starting to sport their own data loggers, notably the Ampair 6000 and the Quiet Revolution QR5. Whilst it may seem a bit late to measure the wind resource after installation, the patient accumulation of data does allow a picture to be built up of real wind speeds across the world that will be of value to other prospective clients. For this reason internet-enabled devices are likely to become prevalent over the next few years, with built-in mobile telephones to transmit the data to manufacturers, intermediaries, and consumers.
The US Department of Energy (DoE) project aims to build upon the best of the available resource estimators such as these from Cadmus, Encraft, and the Californian SWEET estimator.
Critics of the very cheap PowerPredictor units say that they are not as precise or calibrated. Supporters point out that given the natural annual variation in wind resource at a site, it is not appropriate to over-invest in high precision equipment. Perhaps the biggest advantage of the Power-
renewable energy focus
May/June 2010
39
Wind/small wind
as those proposed by the Carbon Trust. Given that the Carbon Trust is dependent on a proprietary wind atlas and terrain type atlas, this is encouraging news for those who are trying to avoid proprietary lock-in. Looking to the future the industry needs to improve these terrain correction factors further, as otherwise clients will be forced to put up anemometer masts for a year just as they would with a large wind turbine. The US Department of Energy (DoE) is funding an improved wind resource prediction project – Analysis Tool for Distributed Wind Technologies – which comprises a transatlantic consortium with access to much of the UK trial experience – as well as some similar studies in the USA. The team is coordinated by the Cadmus Group of Massachusetts along with the California Wind Energy Cooperative; and has Encraft as the UK coordinator with further UK contributions from Loughborough University, BRE, Ampair and Quiet Revolution. It is hoped that this will result in a globally applicable public domain tool for more accurate prediction.
CFD models Developers of large wind farms invest in computational fluid dynamics (CFD) models such as WASP and WindSim to assess the influence of terrain features and wake effects from other turbines. Conceptually these are no different from the situation faced by small wind turbine owners, albeit that the small wind turbine owner is in a more complex situation – and with less money to spend. In the UK both the BRE and Lougborough University have conducted CFD analyses of various typical individual buildings (and aggregated buildings). These have been validated against wind tunnel testing by both organisations, and the results have been published. Some of them are included within the EST reports and others in academic proceedings.
The smallest units such as this Rutland do not need a site survey with an anemometer before installation.
Predictor approach is that it automates the knowledge-intensive task of data processing, and gives a standardised report at zero cost.
Wind atlases & wind models The existing publicly available wind atlases and wind models are crude. In the UK the publicly available wind atlas (known as NOABL) does not account for terrain types, and so within the installer assessment side of the MCS certification scheme a set of terrain correction factors has been introduced – based upon work carried out by the Building Research Establishment (BRE). The EST trial (a report on the first-ever comprehensive monitoring programme of domestic small scale wind turbines in the UK) suggested that these go a long way towards reducing uncertainty. Further work was presented by Ben Cosh of The Green Company at ISWC 2010, which suggests that these MCS correction factors are at least as good
40
renewable energy focus
May/June 2010
In France and Portugal further work has been carried out by INETI Institute of the Portugese Department of Renewable Energy working in conjunction with the commercial company Meteodyn, which has a commercially available CFD tool, MeteoDyn. INETI is proposing that commercial costs are overcome by running CFD models for all urban areas, and making the results publicly available. There are also research projects under discussion in Spain and USA with CIEMAT and NREL which would look to validate CFD models against full-size buildings that are shaped to enhance windflow. Some other academic institutions around the world have indicated similar interests, including CSTB of France.
Financial advice Installers are rightly pointing out that there is no conceptual difference between selling a pension and selling a wind turbine. In both cases a product costing US$20,000-US$100,000 will yield an annual income of US$2000-US$10,000. In most countries financial advisors are regulated and must be insured so that clients can obtain redress if the financial product does not perform as advertised. Even though a small wind turbine can be sold on the second hand market if the site is not suitable, it is
Wind/small wind
to be expected that over the next few years the installer community will be pressured to give financial performance guarantees. They will therefore be seeking solutions from manufacturers and academics to manage this risk.
Installers are rightly pointing out that there is no conceptual difference between selling a pension and selling a wind turbine. In both cases a product costing US$20,000-US$100,000 will yield an annual income of US$2000-US$10,000. Conclusion Site evaluation remains an art, and for the time being the consumer must either accept this or invest in the time and money required to conduct a full wind monitoring campaign (and associated analysis) for at least one year. If complex CFD simulations are appropriate there are now commercial consultancies which are able to perform them. Consumers need to make an assessment of whether these are cost effective for their project. And if they don’t have the patience to perform cheap data logging using a £100 device, they cannot hold either the manufacturer or installer responsible. Over the next couple of years it is likely that progress will be made regarding site resource evaluation as a result of the broad campaign being taken forward around the world. In the meantime, one should be cautious about unknown independent consultants who assemble marketing literature and internet quotes and deploy them out of context – to the detriment of the small wind industry. Trusted independent experts include Paul Gipe, Mick Sagrillo, Ian Woofend, and Hugh Piggott. And increasingly even these gurus cannot keep track of the many advances that are being made, so the formal committee structures of the American Wind Energy Association (AWEA) and RenewableUK are a vital resource, if the industry is to achieve effective coordination of its endeavours.
About the author: David Sharman is managing director of the UK wind turbine manufacturer Ampair. He serves on a number of small wind turbine committees including the international IEC and IEA committees; the USA NEC committee; and the UK committees of the MCS and RenewableUK. He is a systems engineer with a BEng (Hons) from RNEC Manadon and an MSc from MIT. Prior to Ampair he was an officer in the Royal Navy, and an operations and project manager in Shell. He has lived and worked in many countries around the world including several years in Latin America. This article expresses his personal views.
renewable energy focus
May/June 2010
41