Efficient energy source
It only takes a small amount of flow (as little as two gallons per minute) or a drop as low as two feet to generate electricity with micro hydro. Electricity can be delivered as far as a mile away to the location where it is being used.
Reliable electricity source
Hydro produces a continuous supply of electrical energy in comparison to other small-scale renewable technologies. The peak energy season is during the winter months when large quantities of electricity are required.
No reservoir required
Microhydro is considered to function as a ‘run-of-river’ system, meaning that the water passing through the generator is directed back into the stream with relatively little impact on the surrounding ecology.
Cost effective energy solution
Building a small-scale hydro-power system can cost from $1,000 – $20,000, depending on site electricity requirements and location. Maintenance fees are relatively small in comparison to other technologies.
Power for developing countries
Because of the low-cost versatility and longevity of micro hydro, developing countries can manufacture and implement the technology to help supply much needed electricity to small communities and villages.
Integrate with the local power grid
If your site produces a large amount of excess energy, some power companies will buy back your electricity overflow. You also have the ability to supplement your level of micro power with intake from the power grid.
Micro Hydro Cons – Disadvantages
Suitable site characteristics requiredIn order to take full advantage of the electrical potential of small streams, a suitable site is needed. Factors to consider are: distance from the power source to the location where energy is required, stream size (including flow rate, output and drop), and a balance of system components — inverter, batteries, controller, transmission line and pipelines.
Energy expansion not possible
The size and flow of small streams may restrict future site expansion as the power demand increases.
Low-power in the summer months
In many locations stream size will fluctuate seasonally. During the summer months there will likely be less flow and therefore less power output. Advanced planning and research will be needed to ensure adequate energy requirements are met.
Environmental impact
The ecological impact of small-scale hydro is minimal; however the low-level environmental effects must be taken into consideration before construction begins. Stream water will be diverted away from a portion of the stream, and proper caution must be exercised to ensure there will be no damaging impact on the local ecology or civil infrastructure.
Misconceptions – Myths about hydro power
Small streams do not provide enough force to generate powerThe Truth: Energy output is dependant on two major factors: the stream flow (how much water runs through the system) and drop (or head), which is the vertical distance the water will fall through the water turbine.
A large water reservoir is required
The Truth: Most small-scale hydro systems require very little or no reservoir in order to power the turbines. These systems are commonly known as ‘run-of-river’, meaning the water will run straight through the generator and back into the stream. This has a minimal environmental impact on the local ecosystem.
Hydro generators will damage the local ecosystem
The Truth: Careful design is required to ensure the system has a minimal impact on the local ecology. A small amount of energy compromise may result, but this will ensure that the project does not have an effect on local fish stocks. The Environment Agency requires that stream levels must be maintained at a certain level in order to sustain the life within. Since there is no loss of water in the generation process, these requirements can easily be met.
Micro hydro electricity is unreliable
The Truth: Technology advances (such as maintenance-free water intake equipment and solid-state electrical equipment) ensure that these systems are often more reliable in remote areas. Often these systems are more dependable than the local power main.
The electricity generated is low quality
The Truth: If the latest electronic control equipment, inverters and alternators are used, the resultant power supply has the potential to be of higher quality the main electrical power grid.
Hydro power is free
The Truth: Micro power development can be cost-intensive to build and maintain. There are some fixed maintenance costs. These costs vary according to site location and material requirements.
Microhydro Electricity Basics
By Paul Cunningham & Ian WoofendenHydropower is based on simple concepts. Moving water turns a turbine, the turbine spins a generator, and electricity is produced. Many other components may be in a system, but it all begins with the energy already within the moving water.
Water power is the combination of head and flow. Both must be present to produce electricity. Consider a typical hydro system. Water is diverted from a stream into a pipeline, where it is directed downhill and through the turbine (flow). The vertical drop (head) creates pressure at the bottom end of the pipeline. The pressurized water emerging from the end of the pipe creates the force that drives the turbine. More flow or more head produces more electricity. Electrical power output will always be slightly less than water power input due to turbine and system inefficiencies.
Head is water pressure, which is created by the difference in elevation between the water intake and the turbine. Head can be expressed as vertical distance (feet or meters), or as pressure, such as pounds per square inch (psi). Net head is the pressure available at the turbine when water is flowing, which will always be less than the pressure when the water is turned off (static head), due to the friction between the water and the pipe. Pipeline diameter has an effect on net head.
Flow is water quantity, and is expressed as "volume per time," such as gallons per minute (gpm), cubic feet per second (cfs), or liters per minute (lpm). Design flow is the maximum flow for which your hydro system is designed. It will likely be less than the maximum flow of your stream (especially during the rainy season), more than your minimum flow, and a compromise between potential electrical output and system cost.
Measuring Head & Flow
Before you can begin designing your hydro system or estimating how much electricity it will produce, you´ll need to make four essential measurements:
• Head (the vertical distance between the intake and turbine)
• Flow (how much water comes down the stream)
• Pipeline (penstock) length
• Electrical transmission line length (from turbine to home or battery bank)
Head and flow are the two most important facts you need to know about your hydro site. You simply cannot move forward without these measurements. Your site´s head and flow will determine everything about your hydro system—pipeline size, turbine type, rotational speed, and generator size. Even rough cost estimates will be impossible until you´ve measured head and flow.
When measuring head and flow, keep in mind that accuracy is important. Inaccurate measurements can result in a hydro system designed to the wrong specs, and one that produces less electricity at a greater expense.
Microhydro-Electric System Types
Off-Grid Battery-Based Microhydro-Electric SystemsMost small off-grid hydro systems are battery-based. Battery systems have great flexibility and can be combined with other energy sources, such as wind generators and solar-electric arrays, if your stream is seasonal. Because stream flow is usually consistent, battery charging is as well, and it´s often possible to use a relatively small battery bank. Instantaneous demand (watts) will be limited not by the water potential or turbine, but by the size of the inverter.
The following illustration includes the primary components of any off-grid battery-based microhydro-electric system. See our Microhydro-Electric System Components section for an introduction to the function(s) of each component.
Off-Grid Batteryless Microhydro-Electric Systems
If your stream has enough potential, you may decide to go with an AC-direct system. This consists of a turbine generator that produces AC output at 120 or 240 volts, which can be sent directly to standard household loads. The system is controlled by diverting energy in excess of load requirements to dump loads, such as water- or air-heating elements. This technique keeps the total load on the generator constant. A limitation of these systems is that the peak or surge loads cannot exceed the output of the generator, which is determined by the stream´s available head and flow. This type of system needs to be large to meet peak electrical loads, so it can often generate enough energy for all household needs, including water and space heating.
The following illustration includes the primary components of any off-grid batteryless microhydro-electric system. See our Microhydro-Electric System Components section for an introduction to the function(s) of each component.
Grid-Tied Batteryless Microhydro-Electric Systems
Systems of this type use a turbine and controls to produce electricity that can be fed directly into utility lines. These can use either AC or DC generators. AC systems will use AC generators to sync directly with the grid. An approved interface device is needed to prevent the system from energizing the grid when the grid is out of action and under repair. DC systems will use a specific inverter to convert the output of a DC hydro turbine to grid-synchronous AC. The biggest drawback of batteryless systems is that when the utility is down, your electricity will be out too. When the grid fails, these systems are designed to automatically shut down.
The following illustration includes the primary components of any grid-tied batteryless microhydro-electric system. See our Microhydro-Electric System Components section for an introduction to the function(s) of each component.
Understanding the basic components of an RE system and how they function is not an overwhelming task. Here are some brief descriptions of the common equipment used in grid-intertied and off-grid microhydro-electric systems. Systems vary—not all equipment is necessary for every system type.
Intake
Pipeline
Turbine
Controls
Dump Load
Battery Bank
Metering
Main DC Disconnect
Inverter
AC Breaker Panel
Kilowatt-Hour Meter
Intake
AKA: screen, diversion, impoundment
Intakes can be as simple as a screened box submerged in the watercourse, or they can involve a complete damming of the stream. The goal is to divert debris- and air-free water into a pipeline. Effectively getting the water into the system´s pipeline is a critical issue that often does not get enough attention. Poorly designed intakes often become the focus of maintenance and repair efforts for hydro-electric systems.
A large pool of water at the intake will not increase the output of the turbine, nor will it likely provide useful storage, but it will allow the water to calm so debris can sink or float. An intake that is above the bottom of the pool, but below the surface, will avoid the grit on the stream bottom and most of the floating debris on top. Another way to remove debris is to direct the water over a sloped screen. The turbine´s water falls through, and debris passes with the overflow water.
Pipeline
AKA: Penstock
Most hydro turbines require at least a short run of pipe to bring the water to the machine, and some turbines require piping to move water away from it. The length can vary widely depending on the distance between the source and the turbine. The pipeline´s diameter may range from 1 inch to 1 foot or more, and must be large enough to handle the design flow. Losses due to friction need to be minimized to maximize the energy available for conversion into electricity. Plastic in the form of polyethylene or PVC is the usual choice for home-scale systems. Burying the pipeline is desirable to prevent freezing in extremely cold climates, to keep the pipe from shifting, and to protect it from damage (cows, bears, etc.) and ultraviolet (UV) light degradation.
Turbine
AKA: Waterwheel
The turbine converts the energy in the water into electricity. Many types of turbines are available, so it is important to match the machine to the site´s conditions of head and flow.
In impulse turbines, the water is routed through nozzles that direct the water at some type of runner or wheel (Pelton and Turgo are two common types). Reaction turbines are propeller machines and centrifugal pumps used as turbines, where the runner is submerged within a closed housing. With either turbine type, the energy of the falling water is converted into rotary motion in the runner´s shaft. This shaft is coupled directly or belted to either a permanent magnet alternator, or a "synchronous" or induction AC generator.
Controls
AKA: Charge controller, controller, regulator
The function of a charge controller in a hydro system is equivalent to turning on a load to absorb excess energy. Battery-based microhydro systems require charge controllers to prevent overcharging the batteries. Controllers generally send excess energy to a secondary (dump) load, such as an air or water heater. Unlike a solar-electric controller, a microhydro system controller does not disconnect the turbine from the batteries. This could create voltages that are higher than some components can withstand, or cause the turbine to overspeed, which could result in dangerous and damaging overvoltages.
Off-grid, batteryless AC-direct microhydro systems need controls too. A load-control governor monitors the voltage or frequency of the system, and keeps the generator correctly loaded, turning dump-load capacity on and off as the load pattern changes, or mechanically deflects water away from the runner. Grid-tied batteryless AC and DC systems also need controls to protect the system if the utility grid fails.
Dump Load
AKA: diversion load, shunt load
A dump load is an electrical resistance heater that must be sized to handle the full generating capacity of the microhydro turbine. Dump loads can be air or water heaters, and are activated by the charge controller whenever the batteries or the grid cannot accept the energy being produced, to prevent damage to the system. Excess energy is "shunted" to the dump load when necessary.
Battery Bank
AKA: storage battery
By using reversible chemical reactions, a battery bank provides a way to store surplus energy when more is being produced than consumed. When demand increases beyond what is generated, the batteries can be called on to release energy to keep your household loads operating.
A microhydro system is typically the most gentle of the RE systems on the batteries, since they do not often remain in a discharged state. The bank can also be smaller than for a wind or PV system. One or two days of storage is usually sufficient. Deep-cycle lead-acid batteries are typically used in these systems. They are cost effective and do not usually account for a large percentage of the system cost.
See also the following Home Power feature articles:
Metering
AKA: battery monitor, amp-hour meter, watt-hour meter
System meters measure and display several different aspects of your microhydro-electric system´s performance and status—tracking how full your battery bank is, how much electricity your turbine is producing or has produced, and how much electricity is being used. Operating your system without metering is like running your car without any gauges—although possible to do, it´s always better to know how well the car is operating and how much fuel is in the tank.
See also the following Home Power feature articles:
The Whole Picture: Computer-Based Solutions for PV System Monitoring
Mutichannel Metering: Beta-Testing a New System Monitor
Control Your Energy Use & Costs with Solar Monitoring
In battery-based systems, a disconnect between the batteries and inverter is required. This disconnect is typically a large, DC-rated breaker mounted in a sheet-metal enclosure. It allows the inverter to be disconnected from the batteries for service, and protects the inverter-to-battery wiring against electrical faults.
Inverter
AKA: DC-to-AC converter Inverters transform the DC electricity stored in your battery bank into AC electricity for powering household appliances. Grid-tied inverters synchronize the system´s output with the utility´s AC electricity, allowing the system to feed hydro-electricity to the utility grid. Battery-based inverters for off-grid or grid-tied systems often include a battery charger, which is capable of charging a battery bank from either the grid or a backup generator if your creek isn´t flowing or your system is down for maintenance.
In rare cases, an inverter and battery bank are used with larger, off-grid AC-direct systems to increase power availability. The inverter uses the AC to charge the batteries, and synchronizes with the hydro-electric AC supply to supplement it when demand is greater than the output of the hydro generator.
AC Breaker Panel
AKA: mains panel, breaker box, service entrance
The AC breaker panel, or mains panel, is the point at which all of a home´s electrical wiring meets with the provider of the electricity, whether that´s the grid or a microhydro-electric system. This wall-mounted panel or box is usually installed in a utility room, basement, garage, or on the exterior of a building. It contains a number of labeled circuit breakers that route electricity to the various rooms throughout a house. These breakers allow electricity to be disconnected for servicing, and also protect the building´s wiring against electrical fires.
Just like the electrical circuits in your home or office, a grid-tied inverter´s electrical output needs to be routed through an AC circuit breaker. This breaker is usually mounted inside the building´s mains panel. It enables the inverter to be disconnected from either the grid or from electrical loads if servicing is necessary. The breaker also safeguards the circuit´s electrical wiring.
Kilowatt-Hour Meter
AKA: KWH meter, utility meter
Most homes with grid-tied microhydro-electric systems will have AC electricity both coming from and going to the utility grid. A multichannel KWH meter keeps track of how much grid electricity you´re using and how much your RE system is producing. The utility company often provides intertie-capable meters at no cost.
SMALL HYDRO POWER PLANTS
Small and micro or nano hydropower schemes combine the advantages of large hydro on the one hand an decentralized power supply, on the other. They do not have many of the disadvantages, such as costly transmissions and environmental issues in the case of large hydro, and dependence on imported fuel and the need for highly skilled maintenance in the case of fossil fuelled plants. Moreover, the harnessing of small hydro-resources, being of a decentralised nature, lends itself to decentralised utilization, local implementation and management, making rural development possible mainly based on self-reliance and the use of natural, local resources. There are in fact many thousands of small hydro plants in operation today all over the world. Modern hydraulic turbine technology is very highly developed with the a history of more than 150 years. Sophisticated design and manufacturing technology have evolved in industrialised countries over conventional technology the last 40 years. The aim is to achieve higher and higher conversion efficiencies, which makes sense in large schemes where 1 percent more or less may mean several MW of capacity. As far as costs are concerned, such sophisticated technology tends to be very expensive. Again, it is in the big schemes where economic viability is possible. Small installations for which the sophisticated technology of large hydro is often scaled down indiscriminately, have higher capital cost per unit of installed capacity. On the other hand environmental impacts due to small hydro stations are generally negligible or are controllable because of their size. Often they are non-existent.
Small hydro power plants are in large majority connected to the electricity grids. Most of them are of the “run-of-river” type, meaning simply that they do not have any sizeable reservoir (i.e. water not stored behind the dam) and produce electricity when the water provided by the river flow is available but generation ceases when the river dries-up and the flow falls below a predetermined amount. Power can be supplied by a small (or micro) hydro power plant in two ways. In a battery-based system, power is generated at a level equal to the average demand and stored in batteries. Batteries can supply power as needed at levels much higher than that generated and during times of low demand the excess can be stored. If enough energy is available from the water, an alternating current (AC) direct system can generate power. This system typically requires much higher power level than the battery-based system. Small hydropower in developing countries, on the other hand, implies decentralisation. Energy produced is usually supplied to relatively few consumers nearby, mostly with a low-tension distribution network only.
Small hydro schemes have different configurations according to the head. High head schemes are typical of mountain areas, and due to the fact that for the same power they need a lower flow, they are usually cheaper. Low heads schemes are typical of the valleys and do not need feeder canal. Of the numerous factors which affect the capital cost, site selection and basic lay-out are among the first to be considered. Adequate head and flow are necessary requirements for hydro generation.
Most hydro power systems require a pipeline to feed water to the turbine. The exception is a propeller machine with an open intake. The water must pass first through a simple filter to block debris that may clog or damage the turbine. The intake is usually placed off to the side of the main water flow to protect it from the direct force of the water and debris during high flow.
High safety standards in construction works are often not necessary, even the rupture of a small dam would not usually threaten human life, and the risks are smaller anyway if initial costs are kept down. This makes it possible to use mainly local materials and local construction techniques, with a high degree of local labour participation.
Small hydro systems can require more maintenance than comparable wind or photovoltaic systems. It is important to keep debris out of the turbine. This is done by reliable screening and construction of a settling basin. In the turbine itself, only the bearings and brushes will require regular maintenance and replacement.
MICRO HYDRO SYSTEMS
Microhydro systems are defined as hydroelectric systems that produce less than 1000 Watts. At the high end, microhydro systems produce enough power to run three electrically efficient households. No other form of renewable energy is so reliable or powerful for what it costs. Micro hydro system means that the site has either very little fall or very small flow of water, but probably not both. At sites with lower flow rates, systems are usually tied to a battery bank and configured to produce direct current. With larger hydro resources, systems may be configured to produce alternating current without the use of a battery bank. These systems must be able to directly power peak loads. In some case excess power produced is transferred to an alternate load such as a hot water heater. 
A hydropower turbine appropriate for household use can be bought for about USD 1000. These simple units are about the size of a breadbox and use a rewired automobile alternator to produce direct current. The direct current is used to charge batteries, then converted to AC power with an inverter. A typical micro hydro installation diverts a small portion of stream flow across a screen into a water storage e.g. 200 litre drum. The drum acts as a settling basin and the screen collects debris from the water which may clog the intake to the turbine. The water flows from the drum to the turbine through PVC piping (usually 5 to 10 centimetres in diameter), and then returns to the stream. Additional costs for piping, controls, batteries, and wiring vary depending on the particular application, but range from USD 1000 to USD 5000.
Micro hydro turbines come in two basic forms. One uses an alternator, just like an automobile. The other (nano hydro systems) uses a permanent magnet (permag) generator/motor. The alternator based machines are for larger systems producing from 100 to 1000 watts, while the permag units are best suited to systems producing under 80 Watts. Larger systems use shunt diversion for regulation. This prevents overspeeding of the turbine and premature wear of parts. Smaller systems use regulation schemes that unload the alternator when power is not needed. In all cases, these controls need to be user adjustable. Micro hydro systems are easy to fit with batteries. The turbine produces constant power all the time. The battery acts as a “flywheel” to smooth out the inevitable peaks of consumption. Micro hydros refill the batteries almost immediately after even a little power is consumed from the battery. These systems are “shallow-cycling” and ordinary batteries will last a long time. Usually spending money on good pipe and an efficient turbine is more effective than spending it on batteries. In a microhydro system the length and diameter of the pipe must be specified to suit the situation and the turbine. Using long runs of small diameter pipe will make even the finest turbine ineffective.
 | What sets nano hydro systems apart from other hydro generators is the use of permanent magnet generators for the power source. The advantage to this is that no power is fed back into the machine to electrically generate a magnetic field, as is the case with most alternators, so all of what is produced will feed the batteries. The disadvantage of a permag set-up is that the maximum output is limited by the inherent strength of the magnets. Normally that’s not a problem in a nano hydro situation because usually flow and head of water are too small for a larger, more powerful system anyway. |
Most micro and nano hydro systems are battery-based. They require far less water than AC systems and are usually less expensive. Because the energy is stored in batteries, the generator can be shut down without interrupting the power delivered to the loads. Since only the average load needs to be generated in this system, the pipeline, turbine, generator and other components can be much smaller than those in AC system. For conversion of DC battery power to AC output (type of power needed by most of home appliances) inverters are used. The input voltage to the batteries in battery-based system usually ranges from 12 to 48 Volts DC. If the transmission distance is not long then 12 V system is used. For longer transmission distances higher voltage is used.
AC SYSTEMS
Alternating current (AC) hydro power systems are those used by utilities, but it can also be used on a home power scale under the appropriate conditions. In home power scale system power is not sent to the utility grid, but is directly used by a homeowners appliances (load). AC system does not need batteries. This means that the generator must be capable of supplying the continuous demand, including the peak load. The most difficult load is the short-lasting power surge drawn by motors in refrigerators, washing machines and some other appliances. Usually in typical AC system, an electronic controller is keeping voltage and frequency within prescribed limits. The output from hydro power plan can not be stored and any unused power is sent to a “shunt” load, which can be e.g. a hot water heater. There is almost always enough excess power from this type of system to heat domestic hot water and provide space heating as well.
PUMP AS TURBINE
High costs of equipment and civil works, or more generally, the capital-intensive nature of small hydropower plants, has long been a major constraint. However, in many situations it is necessary not only to achieve a better relation of costs compared to other energies, but to reduce them in absolute terms. This is possible to some degree by standardising equipment, but the scope for using such standardised equipment remains limited since no two sites are exactly the same. Efforts at cost reduction through indigenous manufacture are more promising, largely due to much lower labour costs. To make this possible, standards of design, performance and sometimes reliability must be lowered and all unnecessary sophistication avoided. The same is true in civil construction work, where local materials and techniques should be used to the largest possible extent.
In developing countries and especially in rural areas, it is generally recognized that small hydropower may play a significant role. However, high initial investment costs of small hydropower plants have restricted rapid development of this energy potential in many countries. The use of standard pumps as turbines (PAT) may often be an alternative with a considerable economic advantage and might therefore contribute to a broader application of micro-hydropower. Direct drive of machinery, electricity generation (in parallel to a large grid or isolated) or combinations of these are possible just as with a conventional turbine. The only difference is that a PAT cannot make use of the available water as efficiently as a turbine due to its lack of hydraulic controls.
FIELDS OF APPLICATION OF PUMPS USED AS TURBINES
Pumps (rotational fluid machines) are completely reversible and can run effectively as a turbine. Standard pumps not intentionally designed to operate as turbines are now more and more used in small and micro-hydropower schemes due to their advantages mentioned above. However, performance in both modes are not identical although the theory of ideal fluids would predict the same. Without exception, the optimum flow and head in the turbine mode is greater than in pumping mode. The main reason for this difference is related to the hydraulic losses of the machine.
Applications of PAT range from direct drive of machinery in agro-processing factories and small industries (flour mills, oil expellers, rice hullers, saw mills, wood and metal workshops) to electricity generation both in stand-alone and grid-linked stations.
In most instances, no design changes or modifications need to be made for a pump operating as a turbine provided that selection has taken into account the higher operating head and power output of the machine in turbine mode and consequently, nominal turbine speed has been taken well below maximum permissible pump speed. However, a design review is also required to check any adverse effects occurring from the reverse rotation in turbine mode.