Apr 102011
 

HYDROELECTRIC GENERATION

The power of flowing water can be used to generate electricity, or to do other kinds of useful work. Generating electricity in this way is called hydroelectric generation. It can be done anywhere that there is water and a hill or drop for it to run down, such as a drop in an irrigation canal, a place where a river runs through rapids or over a waterfall, or where a dam has backed up water above the level of the river, to name just a few examples. Hydroelectric generating plants come in all sizes from

huge plants that produce more electricity than most nations can use to very small plants that supply electricity for a single house. The smallest hydroelectric plants are often called micro-hydroelectric plants, or micro-hydro for short. Larger plants are usually called mini-hydro plants. Other names for this size of plant are “small-scale hydro” and “small hydro.”

This report deals only with micro-hydroelectric plants. Microhydro is usually defined as having a generating capacity of up to about 15 kilowatts (KW). This is about enough power for 6 or 8 houses in a developed country, or it can provide basic lighting and other services to a village of 50 to 80 houses. Micro-hydro generation is best suited to providing small amounts of power to individual houses, farms, or small villages in isolated areas. Mini-hydro systems are larger. They can range from about 15 KW up to 15,000 KW, which is enough electric power for a medium-sized town, or for a whole rural region. However, the difference between mini-hydro and micro-hydro plants is not just size.

In general, micro-hydro plants use much simpler and lower cost technology than mini-hydro plants. For this reason, micro-hydro plants are usually well suited to village level development and local self-help projects. With their simpler technologies, they can usually be built by people without much special training, using mostly local materials and skills. They are usually lower in cost than mini-hydro and conventional hydro plants, but they are also less efficient, and the quality of the electricity is not as good. Mini-hydro plants, on the other hand, cost more, but they produce the same constant-frequency alternating current (AC) electricity as large electric power systems, so that they can even be interconnected with a larger system.

Micro-hydro plants generally produce low-voltage direct current (DC) electricity, or else low-voltage variable-frequency AC (these technical terms are defined in the section on electric power below). These kinds of electricity are suited to running lights, small motors, and electric cookers, but not to running large motors, many appliances, or most industrial machinery. Perhaps most importantly, micro-hydro plants cannot be interconnected with other generating plants in an electric system the way mini-hydro and large hydro plants can. Special machines called inverters can convert DC power to the AC power used in large electric systems, but these are expensive and have limited capacity. If you expect to need a fairly large amount of power, if you need to interconnect with a power line, or if you require high reliability, you should probably consider mini-hydro instead. Another VITA technical paper, Understanding Mini-Hydroelectric Generation talks about mini-hydro.

HISTORY OF HYDROELECTRIC GENERATION

Water wheels have been used since ancient times to supply power for grinding grain and other laborious tasks. The first modern hydraulic turbines were developed in the first part of the 19th century by Fourneyron in France. These were further developed by a number of researchers during the middle of the century, so that by 1890 most of the types of turbines now in use had been invented. Thomas Edison’s invention of the electric light and of ways to distribute electricity occurred at about the same time, leading to a great boom in hydroelectric development in Europe and North America. Until about the 1920s, most hydroelectric developments were quite small–in the size range which is now called mini-hydro or even micro-hydro. This was for two reasons: people didn’t know how to build really large dams and turbines, and the small electric transmission systems of the time made it difficult to sell large amounts of electricity. Generally, mini-hydro systems would be used to power a town and its surrounding area, while micro-hydro systems were used on isolated farms and ranches to provide power.

During the era of the 1950s and 1960s, advancing technology and cheap oil, combined with improved long-distance electric transmission, made it possible to sell electricity cheaper than the earlier small hydro plants could make it. Many hundreds of small hydroelectric facilities were abandoned or dismantled during this period. With the oil embargo of 1973, which has led to enormous increases in the cost of oil, small hydro once again appears competitive. Many of the early plants which were abandoned in the 1950s and 1960s are now being refurbished, and many new ones are being planned. Small hydro is also well suited for developing countries, and is being actively encouraged by many governments and development organizations in order to reduce oil imports and encourage development. Micro-hydro has a special role to play in developing countries, since it makes it possible to provide lighting, power, and communications (such as television and radio) even in areas far from the main electric power systems. Micro-hydro can thus play an important role in promoting rural development in remote areas.

HYDROPOWER FUNDAMENTALS

This section presents a few basic facts and principles about electric power and hydroelectric generation. Reading it will not make you into a hydroelectric engineer, but it will help you understand how hydroelectric systems work, and what makes a good or a bad hydroelectric site. It will also help you to understand the more detailed technical material that you will need to read if you decide to build a micro-hydro plant.

BASIC PRINCIPLES

Electric Power

Power is defined as an amount of energy divided by the time it takes to supply the energy, or in other words as the rate at which energy is delivered. Power is measured in units called watts, or (for large amounts of power) in units of kilowatts.

One kilowatt is equal to 1,000 watts. Power is also measured in horsepower. One horsepower equals 746 watts. Two other quantities that are important in talking about electric power are the electric current and the voltage. Electric current can be thought of as the amount of electricity flowing through a wire (like the amount of water flowing through a pipe), while voltage can be thought of as a measure of how much force is needed to push the current. Current is measured in amperes, or amps for short, while voltage is measured in volts. The electric power (in watts) is equal to the product of the current and the voltage, so that a current of 1 amp with a voltage of 100 volts would give a power of (1 x 100) = 100 watts.

Two types of electricity are commonly used. Alternating current (AC) electricity is generated in a way that makes it change directions (alternate) many times each second. The number of times it changes direction is called the frequency. Direct current (DC) electricity does not change directions; it always flows the same way.

Large electric power systems and many small ones use alternating current, in order to be able to use transformers to change voltages up and down. Transformers will not work with direct current. On the other hand, batteries can produce only DC, so small electric systems which use batteries generally use DC current. AC can be converted into DC using a device called a rectifier, while DC can be changed into AC using an inverter.

Mini-hydro systems, and large electric power systems such as those in cities use alternating current. In these systems, the voltage and frequency of the electricity produced are carefully controlled to keep them constant. Adding more load to an operating power system (such as by turning on more lights) tends to slow the generators down, which causes the voltage and (for AC systems) the frequency to drop. Conversely, shutting off lights will reduce the load, permitting the generator to run faster. These systems must have some kind of an automatic control which detects when the speed changes, and takes action (such as letting more water into a turbine) to bring the generators back up to the right speed. These controls are expensive, and most micro-hydro systems don’t have them. As a result, the generator speed and voltage in micro-hydro systems will change as people turn lights on and off, so it is a good idea to keep this to a minimum. Batteries can help this situation by providing extra power when the system is heavily loaded, and absorbing extra power when it is lightly loaded.

Electrical equipment is rated in terms of the voltage and the type of current it is designed for, and the maximum amount of power it can produce (for a generator) or use (for things that consume electricity, such as motors and light bulbs). A generator with a rating of 5 KW at 100 volts is designed to produce 50 amperes at 100 volts at full load, which is 5,000 watts or 5 KW. The same generator could also produce smaller amounts of power. The amount of power put out by the generator must be equal to the amount of power being used by the electrical equipment connected to it (unless you are using batteries to store some power). The voltage ratings and type of electricity (DC or AC) used for the electrical equipment should always be the same as the voltage and type of electricity being supplied. If you connect a device rated for one voltage to a wire at another voltage, it almost certainly will not work, and the device is very likely to be damaged. The same is true of connecting AC devices to DC. However, many DC devices such as light bulbs and motors can also be used with AC, if the voltage ratings are the same.

The amount of energy produced in a generator or used by an electrical machine can be calculated by multiplying the amount of power used by the length of time that it is used. Energy is measured in units of joules–one joule is equal to one watt times one second. One joule is a very small amount of energy, So we commonly use units like megajoules (one megajoule is one million joules) or kilowatt-hours (abbreviated KWH). A kilowatt hour is equal to one kilowatt provided for one hour, which is 3.6 million joules. As an example, a 5-KW generator, if it ran at full load for one hour, would produce produce five KWH of electric energy. If it ran for two hours, it would produce 10 KWH.

Mechanical Power

Mechanical power is the force that causes machinery and other things to move. The engine of a car produces mechanical power, and so does an electric motor. Mechanical power can easily be converted into electrical power (this is what a generator does), and electrical power can be converted back to mechanical power (this is done by an electric motor). Mechanical and electrical power are measured in the same units–watts and kilowatts.Head, Flow Rate, and Power Output

Water at the top of a hill or drop has energy, called potential energy, because of where it is. This potential energy is measured in terms of the “head,” which is the vertical distance from the water level at the top of the drop to the water level at the bottom.

Figure 1 shows how head is measured.

Typical Micro Hydroelectric System

Typical Micro Hydroelectric System

 

In natural streams, the potential energy or head of the water is dissipated by friction against the stream bed as the water flows downhill, or by turbulence at the bottom. However, if we put in a smooth pipe from the top to the bottom to reduce friction, and then put in a water turbine at the bottom, we can use the head in the water to turn the turbine and produce mechanical power. The amount of power we can theoretically get is given by:

[P.sub.th] = F x H x 9.807 (Equation 1)

where [P.sub.th] is the theoretical power output in watts, F is the rate of flow of water through the pipe in liters per second, H is the head in meters, and 9.807 is the conversion factor that accounts for the force of gravity on the water.

However, turbines and generators are not perfectly efficient, so the amount of electric power we can actually get from a microhydro plant with a given head and flow rate is less than [P.sub.th]. This amount is given by:

[P.sub.act] = [P.sub.th] x [E.sub.t] x [E.sub.g] x [E.sub.s] (Equation 2)

where [P.sub.act] is the actual useful power output from the plant, [E.sub.t] is the efficiency of the turbine, [E.sub.g] is the efficiency of the generator, and [E.sub.s] is the efficiency of the rest of the electrical system.

Efficiencies are always less than 1.0. Typically, [E.sub.t] is about 0.85 for turbines from a specialized manufacturer, 0.6 to 0.8 for pumps used as turbines, and 0.5 to 0.7 for locally-built cross-flow turbines. [E.sub.g] is usually 0.9 or more, for most kinds of generators. [E.sub.s] will be about 0.9, unless you are transmitting power a great distance, or you are using an inverter, in which case it may be less.

Thus, a flow of 100 liters per second, with a head of 10 meters, could theoretically produce 100 x 10 x 9.807 = 9,807 watts, or 9.807 KW. With a turbine efficiency of 0.75, a generator efficiency of 0.9, and a system efficiency of 0.9, we would actually get 9,807 x 0.75 x 0.9 x 0.9 = 5,958 watts of useful power. The rest would be lost due to inefficiencies in the system.

MICRO-HYDROELECTRIC SYSTEMS AND COMPONENTS

There are many variations of micro-hydro systems. Some of the factors that will affect the kind of system you decide to build are: the amount of power you need; the amount of flowing water available; the available head; the source of the water (from an irrigation canal, a pipeline, behind a dam, or from a free-flowing river or stream); how much money you can afford to spend; and the manual skills and local materials available to you. This section describes the major components of a micro-hydro system, and explains some of the different choices.

BASIC SYSTEM LAYOUT

All micro-hydro systems, whatever their other differences, have a number of features in common. Each must have a source of water, and a place to put the water afterwards (the discharge). The source must be higher than the discharge; the greater the difference in height, the greater the available head will be. In addition, there must be some means of getting the water from the source to the power-plant, and then from the power plant to the discharge. Finally, there must be the power plant itself, which will contain one or more turbines driven by the flowing water, and one or more generators driven by the turbines. Alternatively, the turbines can supply mechanical power to drive some other machinery, such as a mill or saw, directly, without converting the mechanical power into electrical power and back. Sometimes, systems are arranged to supply mechanical-power-during the day, and then supply electricity for lighting at night.

Figure 2 is a sketch of a typical micro-hydroelectric system, showing the major components. Not all systems will have all of these components, however.

A Micro Hydro Power System

A Micro Hydro Power System

 

Beginning at the source of the water, the water must first be collected and channelled to the turbine. Water may be backed up behind a dam (as shown in Figure 2), or diverted out of a flowing stream by some kind of diversion structure. After it is diverted, it flows into a canal, called the headrace until it is directly uphill from the power plant. Once there, the water enters the penstock, which is the pipe leading to the turbine. Alternatively, the penstock may go all the way to the source, eliminating the need for the headrace. In some systems with low head, there may not be a penstock–water from behind a dam may simply flow straight into the turbine. After leaving the turbine, the water passes out through the draft tube into the tailrace, which is a canal leading to the discharge point. The powerhouse is usually built near the discharge, so the tailrace can be very short, and may be absent completely.

The water flows through the turbine, forcing it to turn. Usually, the flow through the turbine is controlled by one or more valves or gates, which allow the flow to be reduced or shut off completely. The turbine is either connected directly to a generator, or it may be connected by means of gears or belts and pulleys to the generator or other machinery to be driven. The generator, the electric wires, and the other devices associated with them are referred to as the electrical gear. The different kinds of turbines and electrical gear are discussed in more detail below. The structural parts of the hydro plant the dam, headrace, penstock, draft tube, tailrace, and power house are called the civil works, although this term is more common in larger plants than in micro-hydro plants. These are also discussed in more detail below.

Civil works

The extent and the cost of the civil works needed for a microhydro plant vary a great deal, depending on the nature of the site where the plant is located. Generally, the more water-hydropower plants must handle, and the further they must carry it, the more expensive the civil works will be. For this reason, microhydro plants with a lot of head are usually cheaper than low-head plants, since the lower head means a greater amount of water is required. However, many low-head plants can be built to take advantage of existing irrigation and water-supply works, such as dams and canals. Combining micro-hydro with a water supply or irrigation project can also help to make that project more practical, since the power from the hydro plant can help to pay for some of the cost of the total project.

The civil works can usually be built from local materials, using local construction techniques and labor, along with a few imported materials such as cement. The exception to this may be the penstock, which must be able to withstand the pressure of the water. If the head is more than 5 meters, this will require metal pipe. This can be expensive, since a fairly large diameter pipe is required in order to reduce the amount of head lost from friction.

In building the civil works, it is important to have advice from someone who is knowledgeable about dams and canals and other hydraulic structures, since building something to carry flowing water is not the same as building a house or a wall. This is especially true of dams. You should never build a dam across any stream without checking to make sure what is legal in your area, and you should never build a dam more an about 1.5 meters high in flat country, or, in hilly country, and dam that will back up a significant amount of water without advice and supervision from a competent engineer. If a dam should break, it can release water with great violence, and even a seemingly small amount of water can cause enormous destruction and loss of life.

Hydraulic Turbines

A hydraulic turbine is a machine which converts the head or potential energy in water flowing through it into mechanical energy (also called work) which is used to turn a shaft. There are a number of different kinds of hydraulic turbines. The two kinds of turbines that are most useful for micro-hydro plants are the Michell or Banki turbine (also called the crossflow turbine) and the Pelton turbine (also called the Pelton wheel). Crossflow turbines are used for low and moderate heads, up to about 40 meters, while Pelton turbines can be used at any head above 20 meters.

Some other types of turbines that are commonly used are propeller or Kaplan turbines for low heads, and Francis turbines for moderate heads. Except for the crossflow turbine, all hydraulic turbines are high-technology items which must be built by a specialized manufacturer. A list of manufacturers of small-turbines-is given in the appendix.

Crossflow turbines can be built by a local machine shop, but a specialized manufacturer may be able to make a more efficient unit. Low-Cost Development of Small Water Power Sites gives instructions for building a crossflow turbine. In response to the increasing interest in small hydro, a number of manufacturers have recently begun to come out with standardized turbines for small hydroelectric plants. Since each turbine does not need to be individually designed and built, this reduces the turbine’s cost significantly. These turbines are normally sold as part of a package, which includes a generator and control system. These packages usually produce high-quality AC power, the same as is available from electric utilities, but they are fairly expensive, especially in micro-hydro sizes.

It is also possible to use ordinary rotating water pumps as hydraulic turbines. Typically, a pump uses mechanical power to increase the head of the water being pumped. By reversing this process, a pump can convert head into mechanical power. Since pumps are mass-produced in great quantities, their cost can be less than a third of a specially-made turbine. However, this lower cost must be balanced against a generally lower efficiency, which reduces the amount of power you can get from a given amount of water. Nevertheless, if you have plenty of water a pump can be a very low-cost choice, especially if you can get one second hand. Most pumps work best as turbines when the head of the water going through them is about 30 to 60 percent greater than the head they were designed to produce as pumps. A local pump dealer or serviceman can provide more information.

Electrical Gear

The electrical gear or electrical system for a micro-hydro system consists of the electric generator, other electrical devices in the powerhouse, and electric wires that take the electricity from the powerhouse to the place where it is to be used. There are a number of different possible arrangements for this. One of the most common arrangements for micro-hydro systems is a low-voltage DC system, similar to an automobile’s electrical system. This arrangement can also be used to produce moderate- voltage AC power (like that which is available from an electric utility) by means of an inverter. Another arrangement, which is commonly used in mini-hydro, is to generate moderate-voltage or high-voltage AC directly, using a synchronous generator. A sketch of a low-voltage DC system is presented in Figure 3.

Typical Micro Hydroelectric System

Typical Micro Hydroelectric System

 

This system uses a generator called an alternator, which produces low-voltage AC. This power goes through a rectifier and voltage regulator which convert it to DC, which is then either used directly, or used to charge batteries if more power is being produced than is needed. In many modern alternators, the rectifier and voltage regulator are built in. The batteries then return this power later, when more power is being used than produced. The final link in the system consists of one or more wires going from the batteries to the lights and other items that are to be powered. Alternatively, the system may be connected to an inverter, which converts the low-voltage DC power from the batteries to AC, for use with appliances requiring AC power. In either case, the wires usually go through a fuse or a circuit breaker in order to protect the system from being damaged by a short circuit or overloaded by too much demand.

The low-voltage DC system has many advantages–it is simple and cheap, and can even be made of parts salvaged from an automobile electrical system. However, it requires special low-voltage light bulbs, and motors which are capable of being run with DC. This problem can be eliminated by using an inverter, but this adds to the cost. Low voltage systems also require heavy wire, and it is difficult to transmit low-voltage power for more than a short distance, since the lower the voltage, the higher the losses in the wire will be. If the hydro site is not within about 50 to 100 meters of the place you will use the electricity, you should either use an inverter to produce AC, or generate it directly with a synchronous generator.

Synchronous generators can produce moderate-voltage AC directly, or can produce high-voltage AC which is then converted to moderate voltages with a transformer. The latter is best if you needto transmit power any distance. However, unlike DC systems, AC systems have no place to store electricity, so they must always adjust the amount of power they produce to match the amount being used. This requires a control system, which can add a great deal to the cost of a micro-hydro plant, and which also requires specialized maintenance. It is usually best to buy synchronous generators as part of a “package,” which includes the generator, turbine, and control system. These packages are available from some of the hydro turbine manufacturers listed in the appendix.

Any electrical system requires special knowledge and understanding. This is especially true of high and moderate voltage systems, since these can be very dangerous–causing shocks and electrical fires if they are set up wrong. Low-voltage DC systems are much safer, since it is nearly impossible to be electrocuted¬† by them, but they can still cause fires. You should not work on even a low-voltage system unless you are sure you know what you are doing, and you should not work on a moderate or high-voltage system at all without help from a professional electrician or other knowledgeable person. You should also be very careful to arrange the powerhouse, electric wires, and other parts of the system so that children and animals cannot come into contact with them and be injured.

SYSTEM COSTS, OPERATION, MAINTENANCE, AND OTHER CONCERNS

The cost of a micro-hydro plant will vary, depending on what kind of equipment you use, how much material and equipment you need to buy, how much it costs for the civil works, and other factors. For instance, if you were able to use salvaged pipe to carry water down a steep hill, building the diversion structure, headrace, and tailrace yourself from local stones, and using a second-hand irrigation pump connected to an alternator and battery salvaged from an automobile, your system would cost very little.

On the other hand, if you had to hire a contractor to build a dam, a long headrace canal, powerhouse, and tailrace; then purchased a new hydro-turbine and generator from overseas, you might wind up spending more than $30,000 for a 5-KW generating plant. Of course, any figure between these two extremes would also be possible.

The best sources of price information for hydro turbines and generators are manufacturers. You will need to estimate the cost of the civil works yourself, or talk to a qualified contractor if the job is too complex for you. For the costs of other materials, such as pipe, electric wires, and so forth, it is best to consult local suppliers. Equipment such as alternators, batteries, and rectifiers can be gotten from auto or marine supply stores and places that sell wind generators. The costs for alternators are about $80 for a 500- to 1,000-watt car alternator (including the rectifier and voltage limiter); costs for larger sizes will be more. Batteries cost about $50.00 for a size that holds about 1/2-KWH. Inverters cost about $500 for one with 1-KW capacity.

Maintenance and operation of micro-hydro plants generally takes very little time. It is necessary to check the plant daily to make sure the intake is not getting clogged, and that the system is in good working order. Depending on the design of the plant, you may also need to adjust the intake valve occasionally to match the water flow into the turbine with the amount of power you are using. More extensive maintenance, such as oiling the machinery, tightening any belts, and checking the water level in the batteries should be done every month. It may also be necessary to clean out silt, weeds, and so forth in the civil works, and to repair any leaks or deterioration. This is usually done about once a year or more often if needed.

APPLICATIONS OF MICRO-HYDROELECTRIC GENERATION

Micro-hydropower can be used anywhere that there is flowing water and a difference in elevation for it to run down. However, it is usually not worthwhile building a micro-hydro plant if there is another source of electricity nearby. Thus, micro-hydro is most useful in providing electricity for basic services such as lighting, electric cooking, running small motors like those of sewing machines and electric fans, and running televisions and radios (with special adapters) in isolated rural areas. A hydro turbine can also be used directly to provide mechanical power to drive a machine such as a saw, a mill, a grain huller, or any other low-power machine. In one reported project in Colombia, a village uses a small Pelton turbine to run a sawmill during the day. At night, the same turbine is connected to a generator, providing power for lighting and other uses.

In another set of projects in Pakistan, the government has assisted villages in setting up micro-hydro units, which provide electricity for three or four light bulbs per house. This electricity is also used for small industrial equipment such as arc welders, electric maize shellers, and electric wheat threshers. A number of industries have also been established to use mechanical power from the turbine directly to run equipment such as flour mills, rice hullers, band saws, wood lathes, cotton gins, corn shellers, and grinders.

COMPARISON WITH ALTERNATIVE TECHNOLOGIES

The major use for micro-hydro generation is to provide small amounts of electric power in isolated areas, where other sources of electricity, such as an electric utility, are not available. If an electric utility or some other large electricity source is available, it is almost always cheaper and easier to buy electricity from that source. Where a large source is not available, however, there are still a number of other possibilities. The most important of these are: diesel and gasoline-engine generators, wind-electric generation, photovoltaic cells, and human- or animal-powered generators. These are each discussed below.

DIESEL AND GASOLINE-ENGINE GENERATORS

Diesel and gasoline generators are convenient and cost less to buy than most other means of producing electricity, but they require fuel, which is becoming increasingly expensive. The cost of a diesel generating system is typically $1,000 to $3,000 per kilowatt, depending on the size (small systems cost more per kilowatt), and gasoline generators are even cheaper. However, the cost of supplying diesel fuel for the generator will be at least $0.20 per KWH (for diesel fuel at $0.50 per liter), which amounts to $1,750 for a 1-KW unit running continuously for a year. Gasoline engines are lighter in weight and cheaper than diesels, but also less efficient. The cost would be even greater for them.

WIND-ELECTRIC GENERATION

Wind-electric generation can be a very advantageous form of power production where the wind is strong and reliable. In some cases, wind-electric generators have even been able to compete with conventional large utilities in cost. Generally, a small wind-electric system consists of a wind turbine, which usually looks like an airplane propeller mounted on a pole. These must be purchased. Some other designs of wind turbines use sails and operate at lower speeds. In either type of system, the turbine is used to turn a generator (usually an alternator) that charges batteries and provides electric power directly. These systems are very similar to the kinds of micro-hydro systems using batteries that were described earlier. wind-electric systems can be expected to cost about $2,000 to $4,000 per kilowatt of generating capacity. The cost per kilowatt-hour will vary, depending on the amount of wind. Usually, only about 20 to 30 percent of the total possible KWH per year are actually generated, even in fairly windy locations. Thus a 1-KW unit could conceivably produce 8,760 KWH per year, but would actually produce only about 1,800 to 2,600 KWH.

PHOTOVOLTAIC CELLS

Photovoltaic cells, or solar cells, can change sunlight directly into electricity. This electricity can then be used to charge batteries for nighttime lighting, or it can be used directly to run motors and other small devices during the day. Solar cells are presently an area of great interest in both developed and less-developed countries, and it seems likely that they will eventually make a significant contribution to rural development. However, solar cells are still three to four times too expensive to be practical for most uses. A solar-cell system now costs about $12,000 to $17,000 per peak kilowatt of generating capacity. Since sunlight is not available at night or on cloudy days, however, the actual number of kilowatt-hours generated per year is only about 20 to 30 percent of the maximum–about the same as for wind generators.

Solar cells are most advantageous where very small amounts of power are needed, since their cost per watt does not increase even in very small sizes. A 100-watt hydro plant might not cost much less than a 1,000-watt plant, but a set of solar cells to produce 100 watts costs about one tenth as much as a set to produce 1,000 watts. Thus, if you only need a little power (to charge batteries for a television, for example) solar cells may be the best choice.

HUMAN AND ANIMAL POWER

Humans can generate power by pedaling a bicycle-like apparatus connected to a generator. Animals such as horses and bullocks can also be used to produce power, by having them turn a- crank connected to the generator through speed-increasing gears or pulleys. The original English unit of power, in fact, was the horsepower, which was defined to be roughly the power that a draft horse could supply. One English horsepower is about 750 watts, but this is actually more work than can be expected from most horses. After allowing for the inefficiency of the generator and the gears, it seems likely that only 200 to 300 watts of electricity could be generated per animal. For humans, the amount that can be produced comfortably is even less probably¬†around 50 watts. This would be enough to charge batteries for a radio or television, or to provide a few hours of light, but not for much else. The cost of such a system would be fairly small from nothing at all (using salvaged parts) to U.S. $100 or $200 for a new alternator and batteries. However, don’t forget that both humans and animals require fuel in the form of food.

BUILDING A MICRO-HYDRO PLANT

Building a micro-hydro plant is a complex process that requires a great deal of planning and preparation. The major steps in this process are described below.

PREPARATORY STEPS

Not all of the steps listed below will be necessary in every case. You should use your own judgment, but generally, the larger and more complex your plant will be, the more time you should spend in the preparatory stage.

o Decide how much electric power you will need, and whether you need AC power or low-voltage DC power.

o Find a promising site for your hydro plant. The best sites have a reliable water supply year round and a large vertical drop in a short distance (the more drop, the less water is required).

o Calculate the amount of power available at the site, using Equations 1 and 2 (page 5). Decide whether that will be adequate for your needs. Be sure to consider the efficiency of the equipment in making this decision.

o Make sure that you can install electric wires from the site to the place you want to use the electricity.

o Check for legal and institutional problems with the site you have chosen. Find out what laws you must obey and what licenses you will need to build and run the plant.

o Check for environmental effects of the plant. Some of the concerns here are the effect of the dam on fish, possible flooding of cropland or other valuable land, and the possibility of creating a breeding ground for disease-causing organisms such as water snails if bilharzia or chistomiasis is a problem in your area. Also check for the effects of the environment (e.g., flooding) on the plant.

o Check for bad social effects–people whose use of the stream will be disrupted, women unable to wash clothes on the bank, and so forth. These must be balanced against the positive social effects of electric light, machines, and so forth.

o Estimate the cost of building a hydro plant at the site, and the total amount of energy (in KWH) that the plant will produce per year. Calculate the annual cost of the plant (including loan payments, annual maintenance, and all other costs) and divide by the number of KWH per year to get the cost per KWH.

o Estimate the cost per KWH of other sources of electricity, such as wind or a diesel generator. Also try to estimate the social and environmental effects, and any legal or institutional problems they might have.

o Consider all of the costs, the social and environmental effects, and the different characteristics of the possible alternatives, and decide whether to go ahead with a micro-hydro plant, to investigate some other kind of generator, or to do nothing at all.

DESIGNING THE PLANT AND PLANNING ITS CONSTRUCTION

Assuming you have decided to go ahead with a micro-hydro plant, the next step is to design it. This does not need to be a lengthy project–just make sure you know everything that will be needed, how much it will cost, where you will get it, and when you will need to order it in order for it to arrive on time. Unless you are very confident of your knowledge, you will probably want to get additional help at this point. Some of the books listed in the appendix (especially Low-Cost Development Small Water Power Sites, may be useful to you. If your system will be at all elaborate, and especially if it will involve constructing any dams or canals, it is a good idea to show your plans to a qualified engineer before proceeding.

BUILDING THE PLANT

This phase includes all the things involved in going from the design to the operating plant.

o Prepare a budget and facilities schedule.

o Arrange financing, if you are planning to borrow the money to build the plant.

o Order the turbine, generator, batteries, pipe for the penstock, the inverter, and any other items that you plan to purchase. Allow enough time for delivery–it can take several months to get a hydro turbine. It may be well to use a reverse-operated commercial pump. Commercial pumps, which can also be used as turbines, have much shorter delivery times.

o Take delivery on important components such as the turbine and generator, and make sure that all planning for the civil works is complete.

o Build the dam, powerhouse, headrace, tailrace, and other civil works, and install the penstock and valves.

o Install the turbine, the generator, and the other electrical gear. Test everything thoroughly, first component by component, then the system as a whole.

OPERATING THE PLANT

Make arrangements for regular inspection and maintenance of the plant and the rest of the system, cleaning out the water intakes, oiling the machinery, tightening the belts, etc. Depending on the system, you may also need to check on the water supply, and adjust the intake valves if too much or too little water is being used. This usually takes very little time–a few minutes a day are enough.

You can carry out most of the preparatory steps of this process using this paper. Once you begin designing and building the plant, however, you will need much more help. Some of the books listed in the bibliography may be useful to you. You may also want to talk to local experts, consultants

FOR MORE INFORMATION

The bibliography at the back of this paper lists a number of useful books and magazines which can provide general information, as well as some which give specific directions for evaluating a potential hydro site. This reference list is followed by a list of manufacturers of small hydroelectric equipment, who may be able to provide further information and references.

Hydroelectric equipment in the 0- to 5-RW range tends to be rather expensive if bought from a manufacturer, but is likely to last longer and work better than homemade systems. Manufacturers can also be very helpful in telling you how to go about evaluating a site, setting up and installing their systems, and making sure they work properly. If you are contacting manufacturers about a specific site, you should first find out (at least approximately) the head and either the minimum and maximum flow rates or the amount of power you want to generate. For information on using pumps as turbines, you should contact a local pump supplier, who will be able to get information from the manufacturers.

The best source of information about things like building dams, canals, and other civil works is probably a local builder. Try to find someone who has experience in building irrigation systems or other water systems. The best source of information on generators and electrical equipment is probably a local electric-motor seller or repairman. This person will know how to contact the manufacturers for your specific requirements, and will also be a great help in setting up the electrical system. You can also try to contact electric motor and generator manufacturers yourself. Boating supply stores and auto supply stores are some of the best sources for lights and appliances used with low-voltage DC systems.