Providing access to water is a critical community development task. In most areas, water is not readily available where it is needed for settlements or farming. Sooner or later, community, household, rangeland, or agricultural planners must devise methods of supplying water on site. This means pumping it out of a borehole or well, or diverting it from a spring, lake, stream, or river.
This module is designed to help planners choose effective energy systems to meet their water supply requirements.
Types of Water Supply
There are three general water supply requirements in rural areas:
Community water supply: Communities require water that is clean, uncontaminated, and constant in supply. The amount of water needed depends on the number of people in the settlement. A village of 1,000 people supplied with a modest supply of water requires some 40 cubic meters (40,000 liters) per day.
Livestock water supply: Grazing animals are often kept where there is limited access to surface water (especially in semi-arid areas). Remote, stand-alone pumping systems are vital for the survival of livestock in such conditions.
Irrigation: For modern farming systems, some form of irrigation is required. However, the most common renewable energy sources for irrigation – PV and wind – are rarely economically viable (see Table 1).
The amount of water required in irrigated farms varies widely from season to season, and the output of PV/RET systems is not well-matched to such variations. When farming areas are above 1 hectare (ha), grid electricity or diesel/petrol powered pumps are far more viable (some Far Eastern producers now manufacture small kerosene water pumps that are increasingly popular. Irrigation is generally not economically viable from deep wells or boreholes.
Table 1: Net present comparative costs of 5 energy systems for irrigation
|Energy Source||1 ha
|Grid Electricity (3km extension)||11,000||11,600||13,700|
|Gasoline / petrol||4,400||10,100||31,000|
Source: Whiffen, et al., 1992
Determining Pumping Needs and Water Source Specifics
Pumps should be chosen based on the actual requirements of the site. These include the actual water requirements, site security, the amount of money available, the maintenance, the service available, and the spare parts infrastructure. Hundreds of pumping systems fail in developing countries because they are introduced without a critical understanding of, or attention to, these issues.
Before buying a pump or pumping system, it is wise to visit a water pump supplier familiar with your area to find out what type of pumping systems are already in use.
There are two important prerequisites for community water pumping technology projects:
- Building up community water management infrastructure for maintenance of technology and hygiene standards
- Introduction of socially-acceptable tariffs and/or charges to cover operations and Maintenance (O&M) costs.
Even before choosing a pump type, you need to carefully look at your water needs and the quality of your water source. Suppliers often use the figure m4 (i.e. meters to the fourth power) when calculating pump energy needs; this represents the volume of water (cubic meters, m3) times the static head/vertical lift (meters, m).
2.1 Amount of water needed and variation by month
This is the single most important criterion for selecting pumps, typically provided in cubic meters (m3) or liters (1,000 liters of water = 1 m3). The amount of water required can be calculated by considering the number of people, livestock, or hectares requiring water supply. (see Table 2). Remember that water requirements change seasonally with humans as well as livestock and farming systems.
2.2 Depth of the water (vertical head)
The height that water (given in meters or feet) must be pumped is the second critical factor when choosing pumps. This is the total vertical distance between the pump and the storage container or point of discharge. It may be quite small in the case of surface water, or as high as 200 meters (or more), in the case of a borehole.
2.3 Water storage
Is there a need for water storage? What is the size of the required storage tank? Remember, with pumps that deliver a high volume, there is less of a need for storage. On the other hand, pumps with irregular output, such as wind and PV pumps, require more storage. In such systems, 2 to 5 days is a minimum storage volume.
However, storage can often be more expensive than the rest of the pumping system combined. Given this factor, pumping systems that are incapable of delivering large quantities of water over constant periods (e.g., wind and PV) are often rejected by people over more constant, high volume systems, such as diesel and petrol pumps.
Water Source Characteristics
There are two categories of water sources:
One source of water is via boreholes (deep wells). Designers of pumping systems need to know the daily yield, the drawdown, and the diameter of the borehole. The diameter of existing pipes in the borehole will also need to be considered (see glossary for definitions of these terms).
Details of the borehole, such as salinity, presence of sand/grit, etc are also useful. Many countries require that reports be written and filed for drilled boreholes; these should be provided to pump suppliers and system designers in order to calculate energy requirements and optimal sources.
Surface source water includes rivers, streams, lakes, and dams. Variations in surface height of the water should be noted. As well, the quality of the water (the presence of silt, algae, salinity, etc) should be noted. Contaminated surface water can present human/animal health problems. Muddy or silted water can block the pumping mechanism.
Table 2: Nominal Water Requirements
|Typical Usage||Nominal Daily Water Supply Requirement (liters)|
|Human (subsistence level)||5-7 liters of clean drinking water per person per day are considered “subsistence” by the UN. Does not include water for washing or cleaning.|
|Human (acceptable)||40 liters|
|Irrigation (vegetables) 1 ha||50|
Source: Whiffen, et al.
Considering Technologies Choices
There are a number of technologies for pumping water, ranging from very basic to extremely complicated. The actual choice of pumping technology will depend on your water requirements and the level of infrastructure in your location. Commercially available pumping systems fall into the two classes, mechanical and electrical.
The following pump types are most commonly used for water pumping:
- Hand pumps (mechanical)
- Petrol pumps (mechanical)
- Diesel pumps (mechanical)
- Wind pumps (mechanical)
- Hydraulic rams/hydropower pumps (mechanical)
- Wind electric pumps (electric)
- Photovoltaic pumps (electric)
- Petrol generators/pumps (electric)
- Diesel generator/pumps (electric)
In the case of electricity systems, one of the weakest links in the system is the type of pump, rather than the energy technology. Avoid batteries on pumping systems wherever possible. Where costs permit, pump water to a storage tank that supplies water by gravity, particularly when using an intermittent energy source such as wind or photovoltaics.
Table 3: Pumping Technology Options
|Type of Pump||Head (meters/m)||Comments|
|Hand-pumps||25-35 meters||Compatibility and the ready supply of spare parts critical|
|Diesel pump||Practically no limit||Fuel consumption, availability of spares, O&M costs|
|Gasoline/petrol/kerosene pump||25-35 meters average (can be much greater with higher powered pumps)||Fuel consumption, availability of spares, O&M costs|
|Wind pumps||150 m maximum||Minimum mean wind speed 2.5 m/s|
|Hydro-rams||Depends on head/speed of source||Must be located at site with moving water|
25-100m (flow very low at high heads)
|Minimum mean insolation 4 kWh/m2/day.
Not viable for high heads or flow rates.
Submersible pump must be sealed. Spares must be available.
|Wind electric pump||Limit imposed by electricity generated||Minimum mean wind speed 4 m/s|
|Diesel genset & electric pump||Practically no limit||Fuel consumption, availability of spares, O&M costs. Expensive to use genset unless for other purposes additional to pumping.|
|Gasoline genset & electric pump||Practically no limit||Fuel consumption, availability of spares, O&M costs. Expensive to use genset unless for other purposes additional to pumping.|
PV pumping is a mature technology with scores of quality products available. However, the market for PV pumps has not grown as fast as expected a decade ago. This is largely due to the high investment costs of PV systems, the intermittence of supply (hence, the requirement for, and expense of, storage), the need for sealed submersible pumps, and the lack of information about them.
PV pumping systems typically consist of a PV array, a load matching device, and a motor/pump. Photovoltaic systems have several beneficial features including virtually no recurrent costs. They can be considered for power requirements below 4 kWp, and are attractive below 2 kWp. Most systems are available between 200 and 1500 Wp.
Three typical commercial systems include:
- Multistage centrifugal
- Positive displacement
- Low head surface
Hand pumps have been in use for centuries. Recent efforts by the United Nations, donors, non-governmental organizations (NGOs), and private companies and individuals to extend portable drinking water to all people in the world have resulted in rapid growth in the number of hand pump models.
Most hand pumps are robust. Most models available on the market can be operated by virtually anyone, including children. However, given water volume and head requirements, hand pumping can be a time- and energy-consuming task. Hand pumping is a poor option for those who can afford other options. (for an interesting evaluation of hand pumps in action.
The optimal situation for a hand pump is a shallow, protected well (low head), with a quick recharge of the water table, with the pump situated next to the house or point of use. The pump should be robust, easy to maintain, require as little human energy as possible, and be easy to maintain.
Even more optimal is when the pump in use is used by a number of other households so that spares are readily available (and inexpensive), and technicians are available to maintain and repair the pumps. Several such pumps are available. Prices (excluding the cost of digging the well and protecting it) can be as low as US$ 100, or as high as US$ 1000.
Wind pumps have been used to pump water for a thousand years. Wind has been used for pumping irrigation and drinking water on all continents. A number of technologies, ranging from old robust models developed for ranches and farms in the early part of the 20th Century, to new, sophisticated, and efficient models are widely available throughout the world. Wind pumps are produced in many developing countries, as well as many European, Asian, and Latin American countries.
A wind pump will require a minimum wind speed of 2.5 m/s, and will rarely operate at its prime at speeds lower than 4 m/s. Wind pumps need to be sited directly over, or very near, the well. This restricts their use because often a well site or river is in low areas, or areas surrounded by trees, with poor wind speeds and regimes.
Wind generators are far more flexible in this regard and can provide electricity – not only for water pumping – but for other uses as well. Because of the intermittent nature of wind, storage is required for virtually all wind pumps. This raises the cost considerably. The cost of wind pumps is high.
However, most require relatively little and infrequent maintenance. Intermittence of wind, the generally low rates of discharge, the costs of storage, and the investment cost of the wind pumps discourage their use for potable water compared to other alternatives. There were more than 6 million wind pumps in operation in the United States in 1930.
Today, there are fewer than 50,000. Nearly 10,000 wind pumps were operating in Kenya in 1950, while today there are perhaps fewer than 300. On the other hand, there has been a “renaissance” in wind pumping in South Africa. After a decline similar to that elsewhere in the world, there are now more than 1 million wind pumps in use in South Africa today.
Perhaps the best situation for a wind pump is in an area with a shallow, protected water source, with a steady, reliable wind regime (average wind speeds of 5 m/s). The area would have few surrounding trees, and a large storage facility (at least five days’ supply of water, for periods of calm). The price for such a pump, with 3m blade, excluding well and storage, would range between US$ 750 to US$ 2500, depending upon the height of the tower and the make (imported, locally made, etc.).
Wind turbines produce electricity which can then be used to drive an electric pump (like PV). Wind turbines use pumps similar to PV units. They have the advantage over wind pumps (mechanical) as they can be located in sites with the best wind conditions, and do not need to be located directly over the water source.
Wind turbines require higher mean wind speeds than wind pumps (4 m/s or more). As with wind pumps, the wind regime needs to be studied carefully when choosing this option, and when choosing a site for the turbine.
Hydraulic rams are a tried and true technology that has been in use for several years. Hydrorams use the energy from fast-moving streams to pump water and can pump water upwards of 50 meters or more. A ram must be located either in a fast-moving stream. This limits their application.
Petrol and diesel water pumps have been in use since the early part of the 20th Century. Large, robust irrigation pumps can be found on the Nile that have been in operation for 70 years. New, inexpensive petrol and diesel pumps (and even kerosene pumps) are increasingly available from the Far East and can be purchased in almost any country where irrigation and pumping equipment is sold.
Both petrol and diesel generators can be used to provide electricity for driving pumps. Sealed submersible pumps have proven to be the most robust and cost-effective for small-scale applications, generally for drinking water. Special care should be taken when choosing pumps, and electricity-generating systems should be sized for the pumping load unless other non-pumping applications are required.
Petrol gensets are portable. They are very suitable for small-scale irrigation as they are inexpensive and can be carried to site and back, and can be used to generate electricity for other applications. However, the amount of water they can deliver is relatively limited, and the cost of fuel and spares is relatively high. Moreover, petrol gensets have a relatively short life span, particularly if they are used as base load.
Diesel gensets can deliver high flow rates even at high heads. However, given the cost of diesel gensets, they would never be purchased only for water pumping (as a diesel pump would be a much more sensible technology choice). Their costs and benefits, as with a petrol genset used for pumping, need to be weighed considering their other uses, and not just their use as pumps.
As with wind turbines, and petrol gensets, they do not need to be located directly near water sources, but can be located where they are needed most (e.g., in a camp, a house, a school, a hospital, etc.), with the electric pump supplied by cable.
Pumps & Related Components
The terms and definitions contained herein have been kindly provided with the permission of Dankoff Solar Products, Inc. They provide both the learner and the expert with an excellent base for developing a better understanding of pumping system requirements and applications.
Glossary of Terms and Definitions
Booster Pump: A surface pump used to increase pressure in a water line, or to pull from a storage tank and pressurize a water system. See surface pump.
Centrifugal Pump: A pumping mechanism that spins water by means of an “impeller”. Water is pushed out by centrifugal force. See also multi-stage.
Check Valve: A valve that allows water to flow one way but not the other.
Diaphragm Pump: A type of pump in which water is drawn in and forced out of one or more chambers, by a flexible diaphragm. Check valves let water into and out of each chamber.
Foot Valve: A check valve placed in the water source below a surface pump. It prevents water from flowing back down the pipe and “losing prime”. See check valve and priming.
Positive Displacement Pump: Any mechanism that seals water in a chamber, then forces it out by reducing the volume of the chamber. Examples: piston (including jack), diaphragm, rotary vane. Used for low volume and high lift. Contrast with centrifugal. Synonyms: volumetric pump, force pump.
Impeller: For impeller, see centrifugal pump
Jet Pump: A surface-mounted centrifugal pump that uses an “ejector” (venturi) device to augment its suction capacity. In a “deep well jet pump”, the ejector is down in the well, to assist the pump in overcoming the limitations of suction. (Some water is diverted back down the well, causing an increase in energy use.)
Multi-Stage Centrifugal: A centrifugal pump with more than one impeller and chamber, stacked in a sequence to produce higher pressure. Conventional AC deep well submersible pumps and higher power solar submersibles work this way.
Priming: The process of hand-filling the suction pipe and intake of a surface pump. Priming is generally necessary when a pump must be located above the water source. A self-priming pump is able to draw some air suction in order to prime itself, at least in theory. See foot valve.
Pulsation Damper: A device that absorbs and releases pulsations in flow produced by a piston or diaphragm pump. Consists of a chamber with air trapped within it.
Pump Jack: A deep well piston pump. The piston and cylinder is submerged in the well water and actuated by a rod inside the drop pipe, powered by a motor at the surface. This is an old-fashioned system that is still used for extremely deep wells, including solar pumps as deep as 350 meters.
Sealed Piston Pump: See positive displacement pump. This is a type of pump recently developed for solar submersibles. The pistons have a very short stroke, allowing the use of flexible gaskets to seal water out of an oil-filled mechanism.
Self-Priming Pump: See priming.
Submersible Pump: A motor/pump combination designed to be placed entirely below the water surface.
Surface Pump: A pump that is not submersible. It must be placed no more than about 20 ft. above the surface of the water in the well. See priming. (Exception: see jet pump)
Vane Pump (Rotary Vane): A positive displacement mechanism used in low volume high lift surface pumps and booster pumps. Durable and efficient, but requires cleanly filtered water due to its mechanical precision.
Solar Pump Components
DC Motor, Brush-Type: The traditional DC motor, in which small carbon blocks called “brushes” conduct current into the spinning portion of the motor. They are used in DC surface pumps and also in some DC submersible pumps. Brushes naturally wear down after years of use and may be easily replaced.
DC Motor, Brushless: High-technology motor used in centrifugal-type DC submersibles. The motor is filled with oil, to keep water out. An electronic system is used to precisely alternate the current, causing the motor to spin.
DC Motor, Permanent Magnet: All DC solar pumps use this type of motor in some form. Being a variable speed motor by nature, reduced voltage (in low sunlight) produces proportionally reduced speed, and causes no harm to the motor. Contrast: induction motor
Induction Motor (AC): The type of electric motor used in conventional AC water pumps. It requires a high surge of current to start and a stable voltage supply, making it relatively expensive to run from solar power. See Inverter.
Linear Current Booster: See pump controller. Note: Although this term has become generic, its abbreviation “LCB” is a trademark of Bobier Electronics.
Pump Controller: An electronic device that varies the voltage and current of a PV array to match the needs of an array-direct pump. It allows the pump to start and to run under low sun conditions without stalling. Electrical analogy: variable transformer. Mechanical analogy: automatic transmission.
Pump System Engineering
Friction Loss: The loss of pressure due to flow of water in the pipe. This is determined by 3 factors – pipe size (inside diameter), flow rate, and length of pipe. It is determined by consulting a friction loss chart available in an engineering reference book or from a pipe supplier. It is expressed in PSI (pounds per square inch) or bar (1 bar equals 1 kilogram per square centimeter), or feet or meters (equivalent additional feet of pumping).
Head: See synonym: vertical lift.
Suction Lift: Applied to surface pumps: Vertical distance from the surface of the water in the source, to a pump located above the surface. This distance is limited by physics to around 6 meters (20 feet) at sea level (subtract about 30 cm [1 foot] per 330 meters [1000 foot] altitude) and should be minimized for best results.
Submergence: Applied to submersible pumps: Distance beneath the static water level, at which a pump is set. Synonym: immersion level.
Total Dynamic Head: vertical lift + friction loss in piping (see friction loss).
Vertical Lift: The vertical distance that water is pumped. This determines the pressure that the pump pushes against. Total vertical lift = vertical lift from surface of water source up to the discharge in the tank + (in a pressure system) discharge pressure. Synonym: static head. Note: Horizontal distance does NOT add to the vertical lift, except in terms of pipe friction loss. Nor does the volume (weight) of water contained in pipe or tank. Submergence of the pump does NOT add to the vertical lift.
Water Well Components
Borehole: Synonym for drilled well. A borehole is the common terminology for a drilled well outside of North America.
Casing: Plastic or steel tube that is permanently inserted in the well after drilling. Its size is specified according to its inside diameter.
Cable Splice: A joint in electrical cable. A submersible splice is made using special materials available in kit form.
Drop Pipe: The pipe that carries water from a pump in a well up to the surface.
Perforations: Slits cut into the well casing to allow groundwater to enter. May be located at more than one level, to coincide with water-bearing strata in the earth.
Pitless Adapter: A special pipe fitting that fits on a well casing, below ground. It allows the pipe to pass horizontally through the casing so that no pipe is exposed above ground where it could freeze. The pump may be installed and removed without further need to dig around the casing. This is done by using a 1-inch threaded pipe as a handle.
Safety Rope: Plastic rope used to secure the pump in case of pipe breakage.
Submersible Cable: Electrical cable designed for in-well submersion. Conductor sizing is specified in millimeters, or (in USA) by American Wire Gauge (AWG) in which a higher number indicates smaller wire. It is connected to a pump by a cable splice.
Well Seal: Top plate of well casing that provides a sanitary seal and support for the drop pipe and pump. Alternative: See pitless adapter.
Water Well Characteristics
Driller’s Log: The written form on which well characteristics are recorded by the well driller. In most states, drillers are required to register all water wells and to send a copy of the log to a state office. This supplies hydrological data and well performance test results to the public and to the well owner.
Drawdown: Lowering of level of water in a well due to pumping.
Recovery Rate: Rate at which groundwater refills the casing after the level is drawn down. This is the term used to specify the production rate of the well.
Static Water Level: Depth to the water surface in a well under static conditions (not being pumped). May be subject to seasonal changes or lowering due to depletion.
Wellhead: Top of the well, at ground level.
Cut-In Pressure and Cut-Out Pressure: See pressure switch.
Gravity Flow: The use of gravity to produce pressure and water flow. A storage tank is elevated above the point of use, so that water will flow with no further pumping required. A booster pump may be used to increase pressure. 2.31 Vertical Feet = 1 PSI. See pressure.
Head: See vertical lift and total dynamic head. In water distribution, synonym: vertical drop.
Open Discharge: The filling of a water vessel that is not sealed to hold pressure. Examples: storage (holding) tank, pond, flood irrigation. Contrast: pressure tank.
Pressure: The amount of force applied by water that is either forced by a pump, or by gravity. Measured in pounds per square inch (PSI). PSI = vertical lift (or drop) in Feet / 2.31, or in bar (1 bar equals the equivalent downward force of a vertical shaft of water 10 meters high exerted on one square centimeter of surface).
Pressure Switch: An electrical switch actuated by the pressure in a pressure tank. When the pressure drops to a low set-point (cut-in) it turns a pump on. At a high point (cut-out) it turns the pump off.
Pressure Tank: A fully enclosed tank with an air space inside. As water is forced in, the air compresses. The stored water may be released after the pump has stopped. Most pressure tanks contain a rubber bladder to capture the air. If so, synonym: captive air tank.
Pressure Tank Pre-charge: The pressure of compressed air stored in a captive air pressure tank. A reading should be taken with an air pressure gauge (tire gauge) with water pressure at zero. The air pressure is then adjusted to about 3 PSI lower than the cut-in pressure (see Pressure Switch). If pre-charge is not set properly, the tank will not work to full capacity, and the pump will cycle on and off more frequently.
Water systems planning for communities, refugee camps, settlements, and farms is a complicated process, usually carried out by qualified experts. In rural areas without access to grid power, water supply experts may not have sufficient energy knowledge to select the most appropriate power source for a given pump requirement.
There is a wide range of pumps and pumping equipment, as the pumping module sets out. These range from simple hand pumps to complex wind pumps, and diesel, petrol, kerosene, and electric pumps.
Pumps must be sized according to need, demand, and the technical, financial, and locational aspects relevant to the particular site.