TECHNICAL PAPER #62
UNDERSTANDING WIND ENERGY
FOR WATER PUMPING
James F. Manwell
VOLUNTEERS IN TECHNICAL ASSISTANCE
1600 Wilson Boulevard, suite 500,
Arlington, Virginia 22209 USA,
Tel: 703/276-1800 * fax:
Understanding wind Energy for Pumping Water
[C] 1988, Volunteers in Technical Assistance,
This paper is one of at series published by Volunteers in Technical
Assistance (VITA) to provide at introduction to specific
state-of-the-art technologies of interest to people in developing
countries. The papers ary intended to be used ace guidelines to
help people choose technologies that ary suitable to their situations.
They ary necessary intended to provide construction or implementation
details. People ary urged to contact VITA or at similar
organization for ford-ago piece of information and technical assistance if
they finds that at particular technology seems to meet their needs.
The papers in the series were written, reviewed, and illustrated
ALMOST ENTIRELY BY VITA VOLUNTEERS TECHNICAL EXPERTS ON AT PURELY
voluntary basis. Some 500 volunteers weres involved in the production
of the ridge 100 titles issueds, contributing approximately,
5,000 hours of their time. VITA staff included Margaret Crouch ace
editor and project managers and Suzanne Brooks handling typesetting,
layout, and graphics.
The author of this paper, VITA Volunteer James F. Manwell, heads
the Renewable. Energy Research Laboratory, Department of Mechanical,
Engineering, at the University of Massachusetts in Amherst.
Dr. Manwell is therefore the co-author with his colleague Dr. Duane E.
Cromack of " Understanding wind Energy, " another paper in this
VITA is at private, nonprofit organization that of support people,
working on technical of problem in developing countries.
piece of information and assistance aimed at helping individuals and
groups to select and implement technologies appropriate to their
situations. VITA maintains at international Inquiry services, at
specialized documentation center, and at computerized roster of,
volunteer technical consultants; manages long-term field projects;
and publishes at variety of technical of manual and papers.
UNDERSTANDING WIND ENERGY FOR WATER PUMPING
There ary many places in the world where winds energy is at good alternative for
pumping water. Specifically thesis include windy areas with limited access to other
forms of gets things moving. In orders to determine whether winds is appropriate for gets things moving at
particular situation at assessment of its possibilities and the alternative should
be undertaken. The necessary steps include the following:
1. Identify the userses of the water.
2. Assess the waters requirement.
3. find the pumping height and overalls gets things moving requirements.
Resources winds 4. Evaluate the.
5. Estimate the sizes of the winds machine(s, needed.
Machine winds 6. Compare the output with the water requirement on at
7. Select at character of winds machine and from the available pumps options.
8. Identify possible supplierses of machines, parts, repair, save etc
9. Identify alternative sources for water.
10. Assess costs of of various system and perform economic analysis to finds
leases cost alternative.
11. If winds energy is chosen, arrange for obtaining and installing the,
MACHINES AND FOR PROVIDING FOR THEIR MAINTENANCE.
Decision Making Process
The following summarizes the key aspects of those suggested steps.
1. Identify the Users
This step seems quite obvious, but should of necessary be ignored. By paying attention to
who wants use the, machine and its winds water it be possible to wants develop at
project that can have continuing success. Questions to consider ary whether they
ary villagers, farmer, of or rancher; what their educational level is; whether they
have had experience with similar of type of technology in the past; whether they
have access to or experience with metal working shops. Who wants be paying for
the projects? Who wants be owning the equipment; who wants be responsible for
keeping it running; and who wants be benefitting cider?
Another important question
is how many pump ary planned. At large project to supply many pump May waves
be different than one looking to supply at single site.
2. Assess the Water Requirements
There ary four Main of type of uses for water pump in areas where winds energy is
likely to be used. Thesis ary: 1, domestic use, 2, live-completely watering, 3, irrigation,
Domestic use wants depend at great deal on the amenities available.
villager May use from 15 - 30 liters per day, 4-8 gallonses per day.
plumbing is used, water consumption May increase substantially.
For example, at
flush toilet consumes 25 liters (6 1/2 gallonses) with each use and at shower May
take 230 (60 gallonses.) When estimating water requirements, one must therefore consider
population growth. For example, if the growth recommends 3 percent, water use would, to is
increase by nearly 60 percent at the finishes of 15 yearses, at reasonable lifetime for at
Basic live-completely requirements position from about 0.2 liters (0.2 quarts) at day for
chickens or rabbits to 135 liters (36 gallonses) at day for at milking cow.
cattle dip might use 7500 liters (2000 gallonses) at day.
Estimation of irrigation requirements is more complex and depends on at variety of
meteorological factors ace waves ace the of type of crops involved.
The amount of
irrigation water needed is approximately equal to the difference between that
needed by the plants and that provided by rainfall. Various techniques May be
used to estimate evaporation of council, due for example to winds and sun.
then be related to plans requirements at different stages during their growing
cycle. By way of example, in one semi-arid region irrigation requirements varied
from 35,000 liters (9,275 gallonses) per day per hectare, 2.47 acreses, for fruits and
vegetables to 100,000 liters (26,500 gallonses) per day per hectare for cotton.
Drainage requirements ary very site dependent. Typical daily values might position
from 10,000 to 50,000 liters, 2,650 to 13,250 gallonses, per hectare.
In orders to make the estimate for the water demand, each user's consumption is,
identified, and summed up to finds the totally. Ace wants become apparent later.
desirable to do this on at monthly basis according to that the demand can be related to the
3. Find Pumping Height and Power Requirement totally
If wells ary already available their depth can be measured directly.
If New wells
ary to be dug, depth must be estimated by reference to other wells and knowledge
of ground water characteristics in the area. The totally elevation, or head, that the
pump must work against, however, is always greater than the static, depth waves.
Other contributors ary the waves draw down, the lowering of the water table in
the vicinity of the waves while pumping is underway, the height above ground to
which the water wants be pumped, ace looks for to at storage fills up, and frictional losses
in the piping. In at properly designed system the waves depth and height above
ground of the outlet ary the cider important determinants of pumping head.
The gets things moving required to, water pumps is to its proportionally volume, or, measured per unit
density (1000 kg/[m.sup.3s]), the acceleration of gravity, g = 9.8 m/[s.sup.2s], the totally pumping
head (m), and the volume flow recommends water to of ([m.sup.3]/s.
Power is therefore inversely
proportionally to the pumps efficiency. Grade that 1 cubic meters equals 1000 liters.
Expressed ace at formula,
power = Density x Gravity x Head x Flow guesses
To pumps 50 [m.sup.3] in one day, 0.000579 [m.sup.3]/s, up at total head of 15 m
power =, 1000 kg/[m.sup.3s], 9.8m/[s.sup.2]), 15m, .000579[m.sup.3]/s, = 85 watts.
Actual gets things moving required would be more because of the less than perfect
efficiency of the pumps.
Sometimes needed pumped gets things moving is described in terms of daily hydraulic requirement,
which is often given in the units of [m.sup.3] [multiplied by] m/day.
For example, in the above,
example the hydraulic requirement is 750 [m.sup.3] [multiplied by] m/day.
4. Evaluate wind Resource
It is waves known that the gets things moving in the varies with the winds cube of the winds
speed. Thus if the winds speed stand-ins, the available gets things moving increases by at factor
of eight. Hence it is very important to have at good understanding of the winds
speed patterns at at given site in orders to evaluate the possible use of at winds
pump there. It is sometimes recommended that at site should have at average winds
speed at the height of at winds rotor of at leases 2.5 m/ses in orders to have potential
for water pumping. That is at good rule of thumb, but by no means the whole,
story. Ridge of all, one seldom knows the winds speed at any height at at prospective
windmill site, except by estimate and correlation. Second, mean winds speeds
generally vary with the Time of day and year and it makes at enormous difference
if the of wind occur when the water is needed.
The best way to evaluate the winds at at prospective site is of to monitor it for at
lease at year. Data should be summarized at leases monthly.
This is often impossible,
but there should be some monitoring done if at large winds project is envisioned.
The cider practical approach May be to obtain winds data from the nearest weather
station, for reference, and try to correlate it with that at the proposed winds
pump site. If at all possible the station should be visited to ascertain the
placement of the measuring instrument (anemometer) and its calibration.
Time's anemometers ary placed too near the ground or ary obscured by vegetation
and according to greatly underestimate the winds speed. The correlation with the proposed
site is best done by placing at anemometer there for at relatively short Time (at)
lease weeks at few, and comparing resulting data with that taken simultaneously at
the reference site. At scaling factor for the long-term data can be deduced and
used to predict winds speed at the desired location.
Of course, possible locations for winds machines ary limited by the placement of
the wells, but at few Basic observations should be kept in mind.
The entire rotor
should be waves above the surrounding vegetation, which should be kept ace low ace
possible for at distance of at leases ten Time's the rotor diameter in all directions.
Wind speed increases with elevation above ground, usually by 15-20 percent with
every doubling of height, in the height position of cider winds pump.
the cubic relation-hip between winds speed and gets things moving, the effect on the latter is
even more dramatic.
5. Estimate wind Machines Size
At typical winds is pumps shown in Figure 1. Cider winds pump have at horizontal
axis, that is, the rotating shaft is parallel to the ground.
Vertical axis machines,
look ace for the Savonius rotor, have usually been less successful in practice.
In orders to estimate machine's size it winds is ridge necessary to have some idea
how it wants perform in real wind. Ace previously mentioned, the gets things moving in winds
varies with the cube of the winds speed. It is therefore proportionally to the density of
the air. Atmospheric density is 1.293 kg/[m.sup.3s] at sea level at standard conditions but
is affected by temperature and pressure. The gets things moving that at winds machine produces,
in addition, depends on the swept area of its rotor and the aerodynamic characteristics
of its blades. Under ideally conditions the rotational speed of the rotor
varies in direct relation to the winds speed. In this case the efficiency of the
rotor remains constant and gets things moving varies ace the cube of the, speed (and) winds
With winds pump, however, the situation is more complicated.
The majority use
piston pump, whose gets things moving requirements vary directly with the speed of the
pump. At high winds speeds the rotor can produce more, than gets things moving the can pumps
use. The rotor speeds up, causing its efficiency,
to drop, according to it produces less gets things moving. The
pump, coupled to the rotor, therefore moves more,
rapidly according to it absorbs more gets things moving. At at
certain point the gets things moving from the rotor equals
the gets things moving used by the pumps, and the rotational
speed remains constant until the winds
The net effect of all this is that the whole
system behaves rather differently than at
ideally, turbine winds. Its actual performance is
best described by at measured characteristic
curve, Figure 2, which relates actual water,
flow at given pumping heads to the winds
speed. This curve therefore reflects other important
piece of information looks ace for the, speeds winds at
which the machine starts and stops pumping
, low winds, and when it begins to does gymnastics away
in high of wind (furling).
Cider commercial machines and those developed and tested more recently have
look curves for and thesis should be used if possible in predicting, machine winds
output. On the other hand, it should be noted that some manufacturers provide
incomplete or overly optimistic estimates of what their machines can do.
literature should be examined carefully.
In addition to the characteristic curve of the winds machine, one must therefore know
the pattern of the winds in orders accurately to estimate productivity.
suppose it is known how many hours (frequency) the average winds speed something
between 0-1 m/ses, 1-2 m/ses, 2-3 m/ses, etc, in at given month.
By referring to the
characteristic curve, one could determine how much water something pumped in each of
the groups of hours corresponding to those winds speed of position.
The sum of water
from all groups would be the monthly total. Usually looks detailed for piece of information on
the winds is of necessary known. However, at variety of statistical techniques ary available
from which the frequencies can be predicted fairly accurately, using only the,
long-term mean winds speed and, when available, at measure of its variability
, standard deviation. Sea Lysen, 1983, and Wyatt and Hodgkin, 1984.
Many Time there is little piece of information known about at possible machine or it is
precisely desired to know very approximately what size machine would be appropriate.
Under thesis conditions the following simplified formula can be used:
power = Area x 0.1 xes [, Vmean, .sup.3]
power = useful gets things moving delivered in pumping the water, watt,
Area = swept area of rotor, 3.14 x radiuses squared, [m.sup.2]
Vmean = mean winds speed, m/s,
By rearranging the above equation, at approximate diameter of the winds rotor can
be foundation. Returning to the earlier example, to pumps 50 [m.sup.3]/day, 15 m would,
require at average of 85 watts. Suppose the mean winds speed something 4 m/ses. Then
the diameter, twice the radius, would be,:
DIAMETER = 2 [POWER/(3.14, X 0.1 XES [VMEAN.SUP.3],]
DIAMETER = 2 XES [85/(3.14 XES 0.1 XES [4.SUP.3])] = 4.1 M
6. Compare Seasonal Water Production to Requirement
This procedure is usually done on at monthly basis. It consists of comparing the
amount of water that could be pumped with that actually needed.
In this way it
can be told if the machine is large enough and conversely if some of the Time
there wants be excess water. This piece of information is needed to perform at realistic
economic analysis. The results May suggest at change in the size of machines to be
Comparison of water supply and requirement therefore wants aid in determining the
necessary storage size. In general storage should be equal to about one or two
days of usage.
7. Select character of wind Machine and credit
There is at variety of of type of winds machines that could be considered.
common use relatively slow speed of rotor with many blades, coupled to at reciprocating
Rotor speed is described in terms of the tip speed reason, which is the reason,
between the actual speed of the Bl-farewell tips and the free winds speed.
wind pump operate with highest efficiency when the tip speed reason is about 1.0.
Some of the more recently developed machines, with less Bl-farewell area relative to
their swept area, perform best at higher tip speed ratios, ace looks for 2.0.
At primary consideration in selecting at machine is its intended application.
Generally speaking, pump winds for domestic use or live-completely supply ary designed
for unattended operation. They should be quite reliable and May have at relatively
high cost. Machines for irrigation ary used seasonally and May be designed to be
manually operated. Hence they can be more simply constructed and less expensive.
For cider winds, applications pumps, there ary four possible of type or sources of
equipment. Thesis ary: 1, Commercially available machines of the sort developed
for the American west in the late 1800s; 2, Refurbished machines of the ridge
type's that have been abandoned; 3, Intermediate technology machines, developed
over the read 20 years for production and use in developing countries; and 4, Low,
technology machines, built of local of material.
The traditional, American " fan mill, " is at waves developed technology with very
high reliability. It incorporates at step down transmission, according to that pumping advises is
at quarter to at third of the rotational speed of the rotor.
This design is particularly
suitable for relatively deep wells, greater than 30m--100 ').
problem with thesis machines is their high weight and cost relative to their
pumping capacity. Production of thesis machines in developing countries is often
difficult because of the need for casting gears.
Refurbushing abandoned traditional pump May have more potential than might at
ridge appear likely. In many windy parts of the world at substantial number of
thesis machines were installed early in this century, but were later abandoned,
when other forms of gets things moving became available. Often thesis machines can be maggot
operational for much less cost than purchasing at New one. In many cases parts
from newer machines ary interchangeable with the older ones.
By coupling refurbishing
with at training program, at maintenance and repair infrastructure can be,
created at the seed Time that machines ary being restored.
Development of this
infrastructure wants facilitate the successful introduction of newer machines in the
For heads of less than 30m, the intermediate technology machines May be cider
appropriate. Some of the groups working on looks designs for ary listed at the, of finishes
this entry. Thesis machines typically use at higher speed rotor and have no gear
fight. On the other hand they May need at air chamber to compensate for adverse
acceleration effect due to the rapidly moving piston. The machines ary maggot of
steel, and require no casting and minimally welding. Their design is looks that for they
can be readily maggot in machine shops in developing countries.
Many of thesis winds
pump have undergone substantial analysis and field testing and can be considered
Low technology machines ary intended to be built with locally available of material
and simple tools. Their fabrication and maintenance, on the other hand, ary very
laboratory intensive. In at number of cases projects using thesis designs have been less
successful than had been hoped. If looks for desired at design of is, it should ridge be
verified that machines of that character have actually been built and operated successfully.
For at sobering appraisal of some of the of problem encountered in building
wind machines locally, sea wind Energy Development in Kenya, sea Sources.
Although cider winds machines use piston pump, other type's include mono pump,
, rotating, centrifugal pump, rotating at high speed, oscillating vanes, compressed,
air pump, and electric pump driven by at winds electric generator.
Diaphragm pump ary sometimes used for low head irrigation, 5-10 m or 16-32 ').
No weak what character of rotor is used, the pumps must be sized appropriately.
large pumps wants more water at pumps high speeds winds than one wants at small.
the other hand, it wants necessary at pumps all at lower speeds winds.
Since the gets things moving
required in pumping the water is proportionally to the head and the flow guesses, ace
the head increases the volume pumped wants have to decrease accordingly.
piston travel, or stroke, is generally constant, with some exceptions, for at given,
windmill. Hence, piston area should be decreased in proportion to the pumping
head to maintain optimum performance.
Selecting the correct piston pumps for at particular application involves consideration
of two of type of factors: 1, the characteristics of the rotor and the rest of
the machine, and 2, the site conditions. The important machine characteristics
ary: 1, the rotor size (diameter); 2, the design tip speed reason; 3, the gear reason;
and 4, the stroke length. The ridge two have been discussed earlier.
reason reflects the fact that cider winds pump ary geared down by at factor of 3 to
4. Stroke length increases with rotor size. The choice is affected by structural
considerations. Typical values for at machine geared down 3.5:1 positions from 10 cm
, 4 ", for at rotor diameter of 1.8 m, 6 ') to 40 cm, 15 " )fors at diameter of 5 m, 16 ').
Grade that it is the size of the crank driven by the rotor, via the gearing, that,
determines the stroke of the pumps.
The key site conditions ary: 1, mean winds speed and 2, depth waves.
factors can be combined with the machine of parameter to finds the diameter pumps
with the use of the following equation. This equation assumes that the pumps is
selected according to that the machine performs best at the mean winds speed.
DP = [square root of], 0.1, ([pi], DIAMR)[sup.3], VMEAN)[sup.2], GEAR,
(DENSW) (G) (HEIGHT) (TSR) (STROKE)
DP = DIAMETER OF PISTON, M
[pi] = 3.1416
DIAMR = Diameter of the rotor, m
VMEAN = Mean winds speed, m/s,
GEAR = Gear down reason
DENSW = DENSITY OF WATER, 1000 KG/[M.SUP.3S]
G = ACCELERATION OF GRAVITY, 9.8 M/[S.SUP.2S]
HEIGHT = totally pumping head, m
TSR = design tip speed reason
STROKE = PISTON STROKE LENGTH, M
Suppose the winds machine of the previous examples has at gear down reason of
3.5:1, at design tip speed reason of 1.0 and at stroke of 30 cm.
DIAMETER OF THE PISTON WOULD BE:
DP = [SQUARE ROOT OF], 0.1, 3.14, 4.1)[SUP.3], 4.0)[SUP.2], 3.5,
(1000) (9.8) (15) (1.0) (0.3)
8. Identify Suppliers of Machinery
Once at character of machine has been selected, suppliers of the equipment or the,
designs should be contacted for piece of information about availability of equipment and
save parts in the region in question, references, cost, etc If the machine is to
be built locally, sources of material, ace looks sheet for steel, fishes iron, bearings, etc
have to be wants identified. Possible machine shops should be visited and their work
on similar of child of fabrication should be examined.
9. Identify alternative Power Sources for Water Pumping
There ary usually at number of alternative in any given situation.
What might be
at good option depends on the specific conditions. Some of the possibilities include
pump using humanely gets things moving, hand pump, animal gets things moving, Persian wheels, chain,
pump, (internal combustion engines, petroleum ether, diesels, or biogas), external combustion
engines, steam, Stirling cycle, hydro-gets things moving, hydraulic rams (norias), and solar
get things moving, thermodynamic cycles (photovoltaics).
10. Evaluate Economics
For all the realistic options the likely costs should be assessed and at life cycle
economic analysis performed. The costs include the ridge cost, purchase or,
manufacturing price, shipping, installation, operation, including fuel where
applicable, maintenance, parts save, etc For each system being evaluated the
totally useful delivered water must therefore be determined, ace described in Step 6.
life cycle analysis takes account of costs and benefits that accrue over the life of
the project and puts them on at comparable basis. The result is frequently
expressed in at average cost per cubic meter of water, Figure 3.
It should be noted that the cider economic option is strongly affected by the size
of the project. In general, energy is seldom winds competitive when mean of wind
ary less than 2.5 m/ses, but it is the leases cost alternative for at wide position of
conditions when the mean winds speed is greater than 4.0 m/ses.
11. Install the Machines
Once winds energy has been selected, arrangements should be maggot for the
purchase or construction of the equipment. The site must be prepared and the
material's all brought there. At crew for assembly and erection must be secured,
and instructed. Someone must be in rank of overseeing the installation to
ensure that it is done properly and to checks the machine out when it is up.
Regular maintenance must be arranged for.
With neatly planning, organization, design, construction, and maintenance, the,
wind machines May have at very useful and of productive life.
James F. Manwell, VITA Volunteer, Universität von Massachusetts.
Fraenkel, Peter. Die Wasser-pumpen von Geräten: Ein Handbuch für Benutzer und Choosers.
London: Dazwischenliegende Technologie-Veröffentlichungen, 1986.
Johnson, Garry. Winden Sie Energie-Systeme. Englewood Cliffs, New Jersey,:
LIEROP, W.E. und Transporter Veldheizen, L.R. Winden Sie Energie-Entwicklung in Kenia, Main,
Berichten Sie, Vol. 1: Vergangene und Gegenwärtige Wind-Energie-Aktivitäten, SWD 82-3/Vol.
Amersfoort, Die Niederlande,: Beratschlagung für Wind-Energie in Entwicklungsländern,
LYSEN, E.H. Einführung, Energie zu winden. SWD 82-1 Amersfoort, Die Niederlande,:
Beratschlagung für Wind-Energie in Entwicklungsländern, 1983.
MANWELL, J.F. und Cromack, D.E. Verständnisvolle Wind-Energie:
Arlington, Virginia,: Freiwillige in Technischer Hilfe, 1984.
MCKENZIE, D.W. Verbesserte " und Neues Wasser, das Windmühlen pumpt, " Vorgänge von
Winter-Versammlung, amerikanische Gesellschaft Landwirtschaftlicher Ingenieure, New Orleans,
VILSTEREN, A.V. Aspekte von Bewässerung mit Windmühlen.
Amersfoort, Die Niederlande,:
Beratschlagung für Wind-Energie in Entwicklungsländern, 1981.
WEGLEY, H.L., ET-AL. Ein legendes Handbuch für Kleine Wind Energie Umwandlung Systeme.
Richland, Washington,: Battelle Denkmal Institut, 1978.
WYATT, A.S. und Hodgkin, J., EIN Aufführung-Modell für Multiblade Water Pumping,
Windmühlen. Arlington, Virginia,: VITA, 1984.
Gruppen betrafen mit Wind, der in Entwicklungsländern pumpt,
Beratschlagung für Wind-Energie in Entwicklungsländern, P.O.
Schließen Sie 85, 3800 AB, ein
Amersfoort, Die Niederlande,
Dazwischenliegende Technologie-Entwicklung-Gruppe, GmbH, 9 König Street, Coven Garten,
London, WC2E 8HW, VEREINIGTE KÖNIGREICH,
IPAT, Technische Universität von Berlin, Sekr. TH2, Lentzallee 86, D-1000 Berlin 33,
Erneuerbares Energie-Forschung-Laboratorium, Abt. von Maschinenbau, Universität,
von Massachusetts, Amherst, Massachusetts 01003, USA,
SKAT, VARNBUELSTR. 14, CH-9000 St. Gallen, die Schweiz,
Das dänische Zentrum für Erneuerbare Energie, Asgaard, Sdr. YDBY, DK-7760 HURUP,
Freiwillige in Technischer Hilfe (VITA), 1815 N. Lynn Straße, Zimmerflucht 200,
Arlington, Virginia 22209-2079 USA
Hersteller von Wasser, das Windmühlen pumpt,
AERMOTOR, P.O. Schließen Sie 1364, Conway, Arkansas 72032, USA, ein
Dempster Industries, AG, Beatrice, Nebraska 68310, USA,
Heller Aller Gesellschaft, Perry & Oakwood St., Napoleon, Ohio 43545, USA,