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Authors


K. Latoufis, PhD student and Research Assistant, NTUA National Technical University of Athens, Heroon Polytechniou str. 9, Athens, 15773, Greece, latoufis@power.ece.ntua.gr

A. Gravas, Research Assistant, NTUA National Technical University of Athens, thagkrav@hotmail.com

G. Messinis, Research Assistant, NTUA National Technical University of Athens, gmessinis@power.ece.ntua.gr

N. Hatziargyriou, Professor, NTUA National Technical University of Athens, nhatziar@mail.ntua.gr

Tel: +30 210 7713699

Profile of authors


Kostas Latoufis received his diploma in Electrical and Electronic Engineering from Imperial College London UK, in 2000. He currently works as a Research Assistant in the Electrical Energy Systems laboratory of NTUA and is a PhD student in small wind turbine design in collaboration with the Mechanical Engineering department of NTUA. He is actively involved in appropriate technology applications for small scale renewable energy systems in Greece and Central America.

A. Gravas received his diploma in Electrical and Computer Engineering from the National Technical University of Athens NTUA, Greece, in 2011. He is currently working on an internship in the Electrical Energy Systems laboratory of NTUA and is actively involved in small wind turbine performance test and measurements.

G. Messinis received his diploma in Electrical and Computer Engineering from the National Technical University of Athens NTUA, Greece, in 2011. He currently works as a Research Assistant in the Electrical Energy Systems laboratory of NTUA and is actively involved in small wind turbine generator design.

Nikos D. Hatziargyriou is a Professor at the Power Division of the Electrical and Computer Engineering Department of NTUA. From February 2007 to September 2012, he was Deputy CEO of the Public Power Corporation (PPC) of Greece, responsible for Transmission and Distribution Networks, island DNO and the Center of Testing, Research and Prototyping. He is a Fellow Member of the IEEE, past Chair of the Power System Dynamic Performance Committee and Chair of CIGRE SCC6. He was a member of the EU Advisory Council of the Technology Platform on SmartGrids. He has participated in more than 60 R&DD Projects, and was coordinator of the EU funded “Care”, “More Care”, “Rise”, “Microgrids”, “More Microgrids” and “Merge”. He is an author of more than 250 scientific publications. His research interests include Smartgrids, Microgrids, Distributed and Renewable Energy Sources and Power System Security.

Acknowledgements


The authors would like to thank P. Kotsampopoulos and K. Pantziris who participated in the construction of some of the small wind turbines described in this article as part of their final year thesis in the Electrical and Electronic department of NTUA, and all other undergraduate students who participated in the construction workshops.

Summary


This paper investigates the use of open source hardware small wind turbines for rural electrification purposes. The technology provides the ability to locally manufacture small wind turbines, which enhances socially sustainable and technically reliable village electrification. This paper introduces the concept of open source applications , followed by a presentation of their recent development into open source hardware applications. As a specific case study, open source hardware small wind turbines are discussed further in this context, and the characteristics of the emerging social network that produces this technology are analysed. Finally, this technology is constructed and tested in the Electrical Energy Systems laboratory of the National Technical University of Athens (NTUA) for validating its performance and discussing its suitability in the rural electrification context.

Locally manufactured open source hardware small wind turbines for rural electrification


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Figure 1: The 2.4m diameter 850W small wind turbine installed at NTUA's test site for a period of ten months (Source: NTUA Electric Energy systems laboratory)


An appropriate technology case study: Locally manufactured small wind turbines 


In 2000, Practical Action contracted Hugh Piggott of Scoraig Wind Electric (Piggott 2000) to develop the design manual, The permanent Magnet Generator (PMG): A manual for manufacturers and developers (Piggott 2001). With over 20 years of experience in harnessing electricity from the wind and many self-built designs tested in the field, Hugh Piggott developed a basic design manual aimed at the local production of permanent magnet generators for small wind turbines in developing countries. The manual outlined how to construct low cost axial flux permanent magnet generators of nominal power 200W with the use of simple manufacturing techniques and workshop tools. In conjunction with the Wind rotor blade construction manual (Sanchez Campos et al. 2001) some of the first small wind turbines constructed with the use of manuals were installed in Peru (Ferrer-Martí et al. 2010), later on in Sri Lanka (Dunnet 1999) and in Nepal (Practical Action 2006).

Hugh Piggott continued working on the self-built generator and began to organise technical seminars, where enthusiasts could meet and learn how to build a small wind turbine. This evolved into the second design manual How to Build a Wind Turbine: The Axial Flux Windmill Plans (2005). The design manual contained better designed components, such as the use of neodymium magnets in the generator and the furling tail system but most importantly provided a more comprehensive and detailed text which guided readers through all stages of the construction process, making the design easier to understand and implement; leading to more robust turbines. During the following years, hundreds of do-it-yourself small wind turbines based on this design were constructed. With the growing use of the Internet, the 2005 design manual was available in different places of the world and translated in many languages. Successful applications of these wind turbines were documented on the Internet (fieldlines.com and scoraigwind.co.uk) leading to individuals and groups setting up their own seminars and projects; further spreading the technology. As time passed, self-built small wind turbines of this design were built in all continents.

Rural electrification was an obvious application of this technology; so several NGOs and groups took up the design manual and constructed community small wind turbines locally in developing countries. Wind Aid in Peru, Blue Energy in Nicaragua and COMET‐ME in Palestine, are some of the most active to the present date. Since then, further manuals have been produced and these have provided a reference proving to be valuable tools in spreading this knowledge. As with most appropriate technology applications, the typical process of developing and transferring technologies often only involved the community and collaborating organisation or practitioner, meaning that wide spread communication and dissemination was difficult and only occurred through relevant magazines or the handbooks themselves. This started to change with the emergence of the Internet.

Open source hardware


In recent years, open source hardware has developed rapidly. While initially concerned mostly with electronics, it has also spread to tools and machines such as the RepRap general-purpose 3D printer, among other applications. Open source hardware applications typically have certain design, construction and maintenance characteristics making them more compatible with certain applications. The products are easier to maintain by the users, since they usually have participated in their construction, and are made to suit local conditions, so they have improved adaptation capabilities. The cost of the product is small as much of the making and maintenance is carried out by the users in communication with the open source network.

Transparency in design has encouraged research and development, increasing re-configurability of products while the debugging of processes and equipment is made faster and more effective. An active community of participants who are designers and users of the technology is essential for the network to succeed. Typical limitations include language and cultural barriers, lack of Internet access, lack of collaboration infrastructure such as open design tools and lack of funding.

Open source hardware ideas resemble the underlying concepts of appropriate technology. Appropriate technology aims at encouraging technological change that empowers communities with tools and techniques which have beneficial effects on the distribution of income and productivity, environmental quality, social development and on the distribution of decision making power in accordance with local socioeconomic contexts. With an emphasis on the collective development of a technology through specifically designed web-based tools, and with the use of the Internet for widespread dissemination of this technology, open source hardware can provide a useful platform for appropriate technology applications.

Open source hardware small wind turbines


The vast number of off-grid rural electrification applications waiting to be implemented at a global scale is becoming a driving force for the creation of an open source hardware process. The commercial small wind turbine market is currently not able to provide quality and low cost energy, as the maintenance and support required for these systems is costly for the users and the installation company. Small wind turbine production in a global market increases transportation costs for spare parts and downtime during failure, gradually making local production a most effective option.

The small wind turbine designs presented in manuals have been implemented and tested in large numbers of applications of rural electrification (Taverner-wood 2011). Local production of the small wind turbines satisfies most appropriate technology criteria and can thus provide a sound solution from a socioeconomic point of view.

In recent years, unofficial research and development work has formed around the open source hardware aspects of the design as it has become more prominent on the Internet. This differs from practitioners’ research which is traditionally conducted through manuals and seminars. Discussion forums at fieldlines.com (Otherpower) have become one of the most popular global hubs for information exchange on self-built small wind turbines, while other discussion boards are prominent in many different countries and languages.

Organisations such as Wind Empowerment, aim at providing the financial and human resources needed for the activities of their member organisations; and university research groups in TU Delft, UC Berkley, UPC Barcelona, HTW Berlin, TUoS Sheffield, NTUA and other research centers such as KAPEG in Nepal have included locally manufactured small wind turbine designs, based on the design manuals, in their research activities (Kotsampopoulos et. al 2011).

Local manufacturing of a small wind turbine in the National Technical University of Athens (NTUA) 


In 2011, tests were carried out on the axial flux generator of an 850W (2.4m rotor diameter) small wind turbine and field measurements for connection to the grid for a time period of ten months. The wind turbine was constructed following the process described in Wind Turbine Recipe Book: The Axial Flux Windmill Plans (Piggot 2009), along with some variations described in Homebrew Wind Power (Bartmann 2008). This wind turbine, which has been in operation for 30 months with no failures and with an annual maintenance brake of two days, was constructed by students and used as a prototype small wind turbine to evaluate its performance and validate a basic design from which open source wind turbines could evolve.

Materials and costs


The materials used for construction included wood for the rotor blades and iron, plywood, polyester resin, neodymium magnets and enamel copper wire for winding. Bolts-screws-nuts and electrical conductors were also required. These materials can be sourced locally with the exception of the neodymium magnets that have to be ordered via the phone or the Internet. The rising cost of these magnets, and some cases of corrosion have led groups and individuals to experiment with ceramic and ferrite magnets.

Wooden blades are preferable to cast glass fiber blades as they are cheaper to make in small quantities and require simpler tools and techniques. The wood required for the blades must be strong, slightly flexible, resistant to weathering and light. Wood types with such characteristics exist in many places of the world and it would be better to find a local variety with these characteristics than to order one from abroad.

Water pipes and steel rope guys are the most common and low cost tools for raising small wind turbines; however these can be difficult to find in some locations. Free standing mounting poles and specifically lattice towers are alternatives. Lattice towers can be locally constructed from iron bars and have widely been used for supporting wind-pumping stations. Materials such as bamboo and tree trunks have also been used.

The tilt up of the tower is additionally a point of concern as cost increases considerably with the use of cranes. The appropriate sizing of the cable connecting the battery bank to the turbine is essential in battery based systems as this can affect the overall performance of the turbine. The correctly sized cables provide a good match between the rotor blades and the generator revolutions per minute, particularly in higher wind speeds. This will avoid stalling the blades (Latoufis et al. 2012).

The cost of an 850W rated power at 10m/s (rotor diameter 2.4m) small wind turbine constructed at NTUA can be found in Table 1. The total cost of a typical application that produces electricity for lighting and small home appliances such as laptops, mobile phones chargers, radios and a TV set could reach 2150 Euros (Autumn 2010 prices of materials in Greece) including the cost of raising it, the battery system and the cost of the installation.

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Table 1: Cost of components in Euro (source: NTUA Electric Energy systems laboratory)


Manufacturing process


The small wind turbine consists of the rotor blades, axial flux generator, alternator-mounting frame, tail and vane (Figure 2).

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Figure 2: Parts of the wind turbine (Source: Piggott 2009)



The construction process will be briefly described with emphasis on some construction tips gained from the practical experience of constructing small wind turbines of rated power ranging from 350W to 3kW (rotor diameter 1.2m to 4.34m) in the Electric Energy Systems laboratory of NTUA.

The basic tools needed for the construction consist of a drill press, an electric arc welder, an angle grinder, a jigsaw, a spoke shave, a draw knife, a compass, a verniers caliper, squares, a soldering iron and others, yet these are the most essential. Apart from wood working, which requires a basic familiarization with the tools that can be achieved quickly with the correct guidance, all other techniques used are simple and effective.

The rotor blades are constructed for the designed pitch angle and chord width according to their length by following a few basic construction steps. Usually the blades are made a few centimeters longer than their final lengths because the edges tend to deform during carving. Some wood types will tend to bend as one side is carved due to stresses being released inside the timber. Wood which is as dry as possible should be used to avoid this, although simultaneous carving of both sides should be performed in order to avoid this in total. This is not possible though with the tools and techniques used in this process and would not be worth the money and time invested as the deflection of the blade is only small. Special timber dryers have been constructed for drying wood in some instances. Finally, the three blades are placed together at 120 degrees from each other to form the rotor and held together with two pieces of plywood and screws.

The generator consists of two parts. The stator, which is the static part and encompasses the coils where electricity in produced and the rotor, which is the moving part and encompasses the magnets on the iron disks that produce the rotating magnetic field (Fig.2). The construction of the generator begins with constructing the coil winder. This simple tool is made from wood and threaded rods and consists of three parts: two outer discs and an inner piece, the spacer. The spacer imposes the thickness of the coils and thus of the stator. In order for the constructed coils to have the exact thickness required, the spacer needs to be cut 1mm thinner, because the coils tend to expand slightly when they are removed from the winding tool. In this manner, technical problems in the regulation of the mechanical airgap of the generator can be avoided and thus achieving the rated power of the design at the desired wind speed. The coils are then connected in star connection and set in the mould to be cast with polyester resin to form the stator of the generator.

Difficulties in construction concerning the moulds are not likely to occur. The shapes and dimensions are clearly stated in the manuals and basic tools are used for the drawing and cutting of the plywood moulds. A slight slope must be given to the inside side walls of all moulds, as this will help removing the stator after casting, without damaging them or having to dismantle the moulds.

Attention must be given to the magnet positioning jig which will guide the magnets to the right places on the iron disks, especially if a new design is constructed. In order to avoid misalignment of the rotor magnet disks, one of the threaded rod holes on the rotor must be marked and the centre of a magnet must be aligned to that hole, making it the index hole. If for some reason this is not possible, then the magnet positioning piece needs to be turned over when mounting the magnets on the second disc. A test run before mounting the magnets on the second disk is the best practice to avoid mistakes.

The construction of the generator's frame and of the tail and hinge only require good welding skills that can be attained gradually by practice.

Performance of a locally manufactured small wind turbine in laboratory and outdoor field tests


The 850W generator was placed on a test bench in a laboratory setup (Figure 3a) with accurate measuring equipment and variable connection possibilities. The generator was initially driven without a load in open circuit using a variable speed DC motor drive. The induced EMF voltage was recorded and found to sinusoidal with a 120-degree phase difference and similar root mean square voltages (Figure 3b).

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Figure 3a: Laboratory setup: (1) Variable speed DC motor, (2) Torque meter, (3) 850W SWT generator, (4) Oscilloscope, (5) Three phase ohmic load, (6) Three phase bridge rectifier, (7) 48V Battery, (8) Three phase series inductance, (9) DC ohmic load. (Kotsampopoulos et al. 2011) (Source: NTUA Electric Energy systems laboratory)


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Figure 3b: The induced EMF voltage at each phase with no load


Vibrations and noise were minimal and only notable when the generator was connected to a rectifier, which is known to introduce harmonics in the system.

The small wind turbine was then installed at NTUA's small wind turbine test site for a period of ten months (Figure 1) while measuring electrical and meteorological data (Figure 4) as described in the IEC 61400-12-1 Power performance measurements of electricity producing wind turbines (IEC 2005).

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Figure 4: Meteorological mast : (1) Anemometer, (2) Wind vane, (3) Thermometer, (4) Humidity sensor, (5) Pressure sensor, (6) Lighting rod (Source: NTUA Electric Energy systems laboratory)


The power curve of the wind turbine and the power coefficient (which is the overall efficiency of the turbine i.e. the ratio of power produced by the small wind turbine over the amount of power provided by the wind on the rotor blades) were measured, at a sampling rate of 1Hz (i.e. one sample per second); the power coefficient of 0.3 was measured for the complete system.

The wind turbine reached its nominal power at higher wind speeds than expected and this was due to losses in the grid connection of the wind turbine through a transformer. The passive aerodynamic braking system, the furling tail, was observed to start operating at 11m/s instead of the designed 10m/s, which would be due to a heavier tail and vane. Although the operation of the furling system protects the generator from overheating in high wind speeds, this small deviation will not cause any problems in the operation of the generator since it has been designed to withstand 10% higher currents than the nominal ones.

The power curve of the wind turbine and the power coefficient (which is the overall efficiency of the turbine i.e. the ratio of power produced by the small wind turbine over the amount of power provided by the wind on the rotor blades) were measured, at a sampling rate of 1Hz (i.e. one sample per second); the power coefficient of 0.3 was measured for the complete system.

The wind turbine reached its nominal power at higher wind speeds than expected and this was due to losses in the grid connection of the wind turbine through a transformer. The passive aerodynamic braking system, the furling tail, was observed to start operating at 11m/s instead of the designed 10m/s, which would be due to a heavier tail and vane. Although the operation of the furling system protects the generator from overheating in high wind speeds, this small deviation will not cause any problems in the operation of the generator since it has been designed to withstand 10% higher currents than the nominal ones.

On the long term


Locally manufactured small wind turbines of the design described in this article have proven to be robust machines, although not without their failures. Failures will range from insignificant to severe, depending on a variety of factors ranging from the materials used to construct the turbine and frequency of maintenance, to the skills of the people constructing the turbine. Routine maintenance can be conducted once a year, yet some small wind turbines of this type have been left unattended for years. Local wind conditions will play a major role in the life of the wind turbine as well as local climate conditions. From the experiences of failures gathered by the global social network of users and manufacturers of these turbines, one of the most common problems is corrosion, and especially of the neodymium magnets in applications close to the sea. Many solutions are implemented, such as galvanising the magnet rotor disks, using neodymium magnets with epoxy coatings, and using more adhesive resins for the casting of the rotor disks. Specifically, for the small wind turbine tested in NTUA there was no failure recorded for the operation period of 30 months, although it must be noted that the test site was not close to the sea and had a mean wind speed of 3.2m/s.

Conclusions


The results of the tests proved that this small wind turbine design has good performance characteristics and is robust and cost effective. Commercial small wind turbines, from established manufacturers, of the same rotor diameter that perform according to the manufacturer's data sheets, could cost three to four times more than the cost of materials for manufacturing this design for prices as in Autumn 2010.

The design process closely matches the experimental results, yet it was concluded that there exists a margin in the construction process for some deviations from the design manuals. This can be caused in practice as a result of differences in the materials used or from different levels of construction experience of the producers of the turbine. Yet, these deviations will not affect the performance of the system significantly.

The global network of users, constructors and designers that constitute the open source hardware process described in this article have developed the specific small wind turbine design to suit applications in different environments using different manufacturing techniques and materials depending on local economic, technical and social conditions. By using communication tools such as Internet forums, by sharing values such as cooperation and driven by the common goal of producing electricity in remote areas, they have managed to make small wind turbine technology a technology-in-use which empowers people with the knowledge of locally producing electricity from the wind.

References


Bartmann D., 2008. Homebrew wind power: A hands on guide to harnessing the wind. First edition. Buckville Publications LLC

Dunnett S., Autumn 1999. Small wind generators for battery charging in Peru and Sri Lanka, Boiling Point, Issue No. 43: Fuel options for household energy

Ferrer-Martí L., Garwood A., Chiroque J., Escobar R., Coello J., Castro M., 2010. A Community Small-Scale Wind Generation Project in Peru, Wind Engineering volume 34, No. 3

Hosman N., March 2012, Performance analysis and improvement of a small locally produced wind turbine for developing countries, Faculty of Aerospace Engineering, TU Delft

IEC, 2005. Part 12-1: Power performance measurements of electricity producing wind turbines. International Electrotechnical Commission

Kotsampopoulos P., Messinis G., Gkravas A., Latoufis K., Hatziargyriou N., March 2011. Design, construction, simulation and performance of axial flux small wind turbines, EWEA 2011, Brussels, Belgium

Latoufis K., Messinis G., Kotsampopoulos P., Hatziargyriou N., 2012. Axial flux permanent magnet generator design for low cost manufacturing of small wind turbines, Wind Engineering, Volume 36, No. 4

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Piggott H., June 2001. The Permanent Magnet Generator (PMG): A manual for manufacturers and developers, Scoraig Wind Electric, ITDG

Piggot H., 2009. A wind turbine recipe book: The axial flux windmill plans, Kindle edition
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accessed 15 December 2012

Sanchez Campos T., Fernando S., Piggott H., July 2001. Wind rotor blade construction, ITDG

Taverner-wood H., April 2011. Applications of micro wind: How non-accredited turbines can fulfil user requirements, School of Engineering and Electronics, University of Edinburgh
Last edited by Mohamed Allapitchai .
Page last modified on Wednesday September 4, 2013 16:37:38 GMT.
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