SMALL SCALE WIND ENERGY SYSTEMS
Newsletter April 2000
Perhaps more than for its contents - two rather large contributions -, this autumn issue is notable for being the first one that is simultaneously published on the Internet. Indeed, cyberspace is becoming every day more accessible for us people committed to small-size wind power and with this step, one of our goals has been reached.
Three years back in time when we were shaping a proposal to continue the existing newsletter, we felt stepping-up towards the electronic media would be inevitable. At that time, to create a web-site seemed a very complex business to us that should be left to specialists. We had no idea that the Internet was going to spread so quickly. One year ago we published the older issues of Small Scale Wind Energy Systems at the Arrakis homepage and it wasnt even that difficult. ITDG-Peru has recently renewed its web-site and digitised the HIDRORED magazine, including the SWESS newsletter. GEDA in Gujarat will follow soon.
The primary challenge however, must always be focussed on the progress in real life of those who live on Earth. At the end, we have to transform everything cyberspace brings, into real and tangible solutions. This is not an easy task and we will have to do it ourselves. Finally, only by offering tangible solutions can those, who are not connected, benefit as well.
To complete another two-year cycle financed by our Minister, there is one more issue to go. Among us who work and live with the computer, we are confident that we will go on intensifying the information network. The challenge concerns all people who do not have access to computers. One should avoid that Humanity will soon become divided into those who are connected and those who are not. Next time we tell you.
Traditional windpumping is generally in decline in spite of the existence of a significant market potential. One of the major causes is that existing commercial windpumps are mostly obsolete in design, which makes them more costly than necessary and difficult to handle and install. The new IT Power windpump addresses this problem for the sector of small farmers and communities. By using modern design methods and materials, it tries to combine a high performance with ease of manufacture, low maintenance and high reliability. A key factor throughout the development has been the liaison with potential manufacturers from developing countries.
The programme was supported initially by the European Commission JOULE I R&D Programme and subsequently by DfID (former UK Overseas Development Administration). The latter project consisted of three phases: phase I, running from July 1993 to March 1995, covered the initial development and testing of a preliminary prototype, an introductory contact with potential manufacturers from developing countries and a detailed market survey for windpumps. Phase II, from May 1995 to October 1997, included the continued product development and initial transfer to identified partners. Project phase III, which started in May 1998, focuses on testing the machine under local conditions and on the subsequent commercialisation in the target countries.
The Windpump Concept
The IT Power windpump is innovative in having a transmission mechanism that produces a quasi-constant torque load combined with a speed reduction; this addresses the start-up problems common to traditional windpumps equipped with a piston pump. (One should bear in mind that the starting torque of a piston pump is in the order of 300% of the mean running torque.) The gearbox is known as the Oval Epicyclic Reciprocator (see Figure 1). The gearbox casing rotates about a pinion on the rotor shaft, thereby converting rotary motion directly to a reciprocating motion suitable for driving a standard piston pump.
The preliminary prototype had a 3-m, 16-bladed rotor with a design tip speed ratio of 1.5 that offered a high starting torque at a reduced weight and cost. The three-cornered tower was fabricated from steel angle section and is hinged at the base, allowing for assembly and maintenance of the machine at ground level.
Prototype Testing & Development
The windpump was installed in December 1993 on the test-field at Silsoe College (Cranfield University, UK). The long-term tests confirmed the effectiveness and reliability of the transmission and other substantive design features, inducing DfID to grant additional support for the period May 1995 to October 1997.
In July 1994 representatives from six organisations (from Zimbabwe, Botswana, Indonesia, Mongolia and two from India) were invited to Silsoe for a demonstration seminar. The test results and feedback gave rise to a number of modifications. Most significant was a scaling down of the machine to a rotor diameter of 2 m, which was in accordance with the market study. The tests also revealed a need for further improvement of the gearbox and specifically the drive train. With the smaller rotor size and subsequent torque reduction, it was important to reduce the weight of the gearbox without compromising durability. Other requirements for commercial replication are the design simplicity and the application of commonly available processes and materials, implying a low sensitivity of the system performance on dimensional tolerances.
The original gearbox was directly coupled to the pump rod and comprised a cast-steel casing with internal rack teeth and a central guide cam and. After a careful analysis of the gearbox geometry and load requirements, it was adapted by incorporating an externally toothed rack with plastic gear teeth (nylon or acetal were highlighted as being appropriate for the marginal lubrication conditions expected) and a cast-iron casing. A non-integer speed reduction ratio of 4.9:1 was chosen to ensure that the same gear teeth on the pinion and rack do not mesh each revolution. This contributes to reduced teeth wear.
Vibrational problems, which occurred at high speeds, were solved by limiting the freedom of movement of the gearbox. Various alternative constraint mechanisms were assessed and finally an arrangement was chosen whereby a roller is vertically constrained within a tubular column (see Figure 1). These changes were subsequently implemented in the Phase II prototype.
Qualitatively the performance of the second machine has been excellent as shown during continuing testing in the UK. The gearbox and the constraint mechanism have functioned without any problem and run very smooth; the furling mechanism works fully satisfactorily. Throughout the tests in the UK, a 50-mm bore pump was used with a stroke of 353 mm as dictated by the gearbox. The measured parameters include the wind speed at hub height, the pump stroke rate, the output flow rate and the pressure-simulated pumping head. Data is logged as 10-minute averages calculated from 0.5 Hz instantaneous readings and processed into 0.5 m/s bins using the standard binning technique. At 17.5 m pumping head, the machine demonstrates a starting wind speed of around 3.0 m/s and a furling wind speed of approx. 11 m/s. The maximum hydraulic efficiency is 21%.
Local Manufacturing Partners
Since the involvement of recipients at an early stage is a key aspect for any technology transfer, the Phase I machine was demonstrated to candidate partners as early as 1994. During phase II, other manufacturers (from China, India and South Africa) were invited to the UK. Finally, after an on-site assessment of the local production capabilities by IT Power engineers, a core group of four manufacturers was identified (in China, India, South Africa and Zimbabwe, see previous issue SSWES). The partners signed a confidentiality agreement, giving them access to the drawings. They were expected to each produce a single prototype for in-country field-testing; the costs were met partly by the local manufacturer and partly through a contribution from DfID. On the longer term a license agreement would be made, giving each manufacturer the exclusive right to produce and sell the windpump in their region.
After the installation of the second prototype at Silsoe College, the design drawings were forwarded to the partners to enable local replication. In October 1997, an IT Power engineer paid a visit to each of the partners to gather feedback on the manufacturing experiences and suggestions for further simplification, as well as on the assistance needed for commercialising the windpump. From one country to another, one noticed a considerable variation in available materials, which asked for specifying suitable alternatives; also the local production capabilities and the manufacturing cost of certain components (such as castings) varied considerably. Potential further design enhancements included a ground level furling mechanism and a platform to perform small maintenance actions directly in the tower.
Field Tests and Commercialisation
For the in-country tests a monitoring system was developed in collaboration with Manx Wind Energy (UK). The main requirements were easy shipment from UK to overseas; easy installation on-site; autonomous power supply; simple and reliable means of data storage (not all partners have access to a PC); weatherproof and robust; economical. The system includes an NRG windlogger with anemometer and windvane and a paddle-wheel flow sensor; data storage is performed on a replaceable data plug which is sent to the UK for processing; the electric power is delivered by two small PV-panels.
Testing of the four local windpumps started in March 1999 and will take one full year. The purpose is to have a clear view on the performance under a variety of field conditions and provide input information for finalising the design. The conditions at the four test-sites are quite dissimilar from each other, ranging from water table depths of between 12 m and 40 m and estimated average annual wind speeds of between 3.5 m/s and 6.5 m/s.
Project phase III will also provide ample opportunities to review in detail a number of commercialisation and license issues, such as the partners' capabilities; the question whether the machine is indeed an interesting product for the manufacturer to produce and commercialise under license; to identify improvements to satisfy specific local demands; to learn about the main support issues to be aware of. This project year will also prove necessary to demonstrate the performance and reliability of the windpump to potential customers (private farmers, NGOs, govt. water ministries etc.). Assuming that the field tests are positive, the partners are expected to initiate plans to put the machine into commercial production. As a prelude to this, each partner will undertake a survey to analyse the present market conditions (updating the survey undertaken in 1994) in order to tailor promotional activities.
Paul Cowley, IT Power Ltd.
The Warren, Bramshill Rd
Eversley, Hampshire RG27 0PR, United Kingdom
Phone: ++44-118 973 0073; Fax: ++44-118-973 0820
Email: email@example.com; Web: www.itpower.co.uk)
Figure 1. Upper part of the drive train of the IT Power windpump with the gearbox, connecting rod and pivot connector.
The first windmills that were installed in Misiones in Argentina in 1945, were the North-American Windchargers for battery charging. Alongside, traditional multi-blade windpumps and a number of artisanal windmills, produced by local craftsmen, were found in use.
The Windchargers were rather unsuccessful because of their small size and the relatively high wind speeds (over 4 m/s) they need to work properly. In 1982, we therefore started the design and construction of a three-bladed, 200-watt windmill with a rotor diameter of 3.5 m and an automatic, centrifugal control system. It was destined to the rural development projects called Granjas o Sistemas Modulares Integrados (Integrated Modular Systems). The windmill, installed on top of a 10-m wooden pole, performed without major difficulties for three years, during which it survived about fifteen storms.
In 1987, the national Ministry of Energy founded the National Wind Energy Centre (CREE) in Chubut and started the development of a test bench for small windmills. Together with a local technician we built the YBYTU 7D, a hydraulic windmill with a nominal power of 4 kW and a rotor of 7 m diameter. Later the Faculty of Engineering in Obrera constructed the 5-m diameter YBYTU 5D with a cardanic transmission adopted from car differentials.
The trials helped us to learn about correct test procedures and how to make an effective use of the energy produced; as well as about the functioning of the safety system. The tests at CREE did not proceed because of problems with the design itself, the rotor weight and the excessive wind speeds in the area. The ongoing development was affected by the scarce support obtained from the official programme, which in the end was suspended.
Misiones is intersected by a system of mountain ridges with an altitude between 200 and 800 meter above sea level. The existing wind speed recordings by the Air Force at Posadas Airport refer to an altitude of 100 m. Since no recordings were available from the mountainous area, in the beginning we used self-made anemometers built from small DC-motors and 3-bladed model aircraft propellers. Later, we obtained two anemometers from the Canadian McGill University Brace Research Institute (Montreal), a portable device with a direct, digital reading, and a cup anemometer with a wind-run counter attached. These instruments allowed us to perform measurements at different sites in the province, especially in the mountains.
Prevailing winds in Misiones are south-east and in time shift counter-clockwise towards a north-eastern direction. These winds are relatively weak, between 3 and 5 m/s. The northerly winds and temporary south-eastern winds are above 10 m/s. During the countless storms that hit the region, speeds may be above 100 km/h (27 m/s). The energy density of the prevailing winds is of the order of about 40 W/m2. The northerly and southern winds correspond to a potential of 100 W/m2, which might be used in the rural areas for wood crafting, welding, etcetera.
The frequent storms and gusts put forward the need for rigid and automatically controlled windmills. This leads to a more expensive construction (primarily due to a safety system against overspeeding) and the need for light-weight wood to construct the rotor blades.
The full-scale tests proved to be a delicate issue, urging for extreme caution during operation and maintenance. The lack of experience and adequate equipment caused a lot of problems; more than one rotor blade was destroyed due to the combined effect of the high local winds and an inappropriate support construction. For this reason, it was decided to continue further research by using small wind tunnel models. This procedure proved to be very useful for testing prototypes and instructive for teaching the engineering students at the Faculty.
In 1997, the development of a new windmill was pursued, called the counter-rotating windmill, equipped with two, 3-bladed, mechanically connected rotors, which turn in opposite directions by means of a cardanic transmission. The front rotor size is 5 m, the rear ones is 4 m, adding to a total power output of 4 kW. The safety system includes an automatic pitching hub incorporated in the first rotor (while the rear one is fixed) and a handle for manually turning the windmill head out of the wind.
With a blade chord of 18 cm and a pitch angle of 10 degrees for starting, the original rotor was tuned to the high wind speeds of Chubut. For the wind regime in Misiones, an inverse control strategy was applied: a large setting angle (30 degrees) for starting, which gradually reduces to 10 degrees at nominal speed and even to negative pitching angles for braking action in high winds. In fact, this is the strategy nowadays adopted in large-size wind turbines.
The test runs to determine the performance were quite promising, but further tests are needed to determine the operation of the brake function and the overall functionality in the rural areas.
Now with a record of over 20 years in the field of renewable energy, I admit one would have saved a lot of time and money by building smaller prototypes. Notwithstanding, the publications from CWD from the Netherlands, Jack Parks book and some magazines about hobby windmill designs in the USA, proved to be a great help. Putting their experiences next to mine reinforced my enthusiasm and the hope to get any further. Although by now we have not accessed modern permanent-magnet technology, I believe all our actions were justified. Our group has acquired a lot of knowledge regarding the passionate field of wind energy, and many students from different technical schools as well as from our university had the opportunity to take advantage of this.
(Information: Eric Barney)
Father Schurtemberger from the Driefontein Mission in Zimbabwe (see SSWES, September 1997) told us that we was obliged to leave the country after being threatened with kidnapping and paying a ransom of not less than US$ 70,000.-. He informs us the situation has become very difficult because of the lack of fuel. Since there are several wind energy projects running in this country, of which the continuity is jeopardised, we will try to get back to this in the next issue.
Henk Holtslag (see May 1999 issue), advisor of the Nicaraguan non-governmental organisation CESADE and the AMEC workshop, has undertaken a new trip to Nicaragua, Panama and Peru. The focus is not only on promotion of the rope pump in Central America, buy also to study its use in the north of Peru. Together with ITDG-Limas Mauricio Gnecco, he will provide technical assistance to a windpump producer in the town of Chiclayo, capital of the Lambayeque province. In Panama he is going to work with the National University, where he collaborated in a seminar last year. This new mission to Latin America has received support from the Dutch organisation Dienst over Grenzen (DOG-PSO).
In Kathmandu (Nepal), renewable energy company Solar Energy is planning to extend its current PV-activities to small scale wind energy. A friend of Arrakis, Mr. Jeroen Bremmer from Holland, will start working with this company in November 2000. More information about Solar Energy, headed by two resident Americans, is found at the homepage of the Himalaya Light Foundation (www.hlf.org.np).
"Small Scale Wind Energy Systems" is a half-yearly newsletter co-edited and published in English by GEDA (India) and in Spanish by ITDG (Peru). The English edition is included in GEDA´s magazine FIRKI; the Spanish version appears as a section of ITDG´s HIDRORED. It is financially supported by the Ministry of Foreign Affairs of the Netherlands (NEDA-DML/KM).
Co-ordination and editing: Arrakis, Wilhelminastraat 26, 5141 HK Waalwijk, The Netherlands; phone: +31(40)281 9454; fax: +31(40)281 9602; email: firstname.lastname@example.org; email@example.com. WWW: http://www.arrakis.nl/
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