NOTE: This document was not written by GW Store – Full credit needs to be extended to the papers authors Chris Greacen and Megan Kerins
The original published transcript can be found here: https://energypedia.info/images/c/ca/Pump_as_Turbine_%28PaT%29_Manual.doc
This document is a manual designed to aid in the planning and installation of pico-hydro power systems that will provide remote, rural villages with a reliable supply of electricity. We focus on pump-as-turbine (PAT) systems, referring specifically to the system built by Palang Thai in the village of Mae Wei in northern Thailand. PAT systems are most suited for developing countries where conventional turbines are not as available, and may or may not be the best option for your village. This manual is intended as a step-by-step guide for site assessment, system layout, sizing and purchasing system components, and installation. Some parts of the manual are technical and may be best understood by someone with technical expertise. Additionally, this manual is to be used together with The Pump-as-Turbine Spreadsheet, which will make all necessary calculations for you. Thus, while a mathematical background is not required, some familiarity with spreadsheets is a big help. We hope that you find this manual to be a useful resource in your efforts to design and install a pico-hydro PAT system. Best of luck!
What is Pico-Hydro?
A hydropower system captures the the energy of moving water for some useful purpose. Wherever there are mountains and streams, hydropower can bring low-cost electricity to isolated communities without polluting the air or water. Furthermore, hydropower is a proven technology; people have been obtaining energy from falling water for thousands of years. Hydropower is still being used on many different scales for many purposes, from small grain-grinding facilities to huge hydroelectric dams that provide electricity to entire cities.
Pico-hydro is a term used to describe the smallest systems, covering hydroelectric power generation under 5kW. Depending on its size, a pico-hydro power system may provide a small, remote community with adequate electricity to power light bulbs, radios, and televisions, among other appliances.
Pump-as-Turbine (PAT) Systems
Typical hydropower systems convert the energy of falling water to mechanical energy with a turbine. In some cases, it may be more appropriate to replace the turbine with a centrifugal water pump, and run it in reverse. The words ‘pump’ and ‘turbine’ are used interchangeably in this manual, as are the words ‘motor’ and ‘generator’. Using a pump as a turbine has numerous benefits for rural pico-hydro projects in the developing world. Since centrifugal water pumps can usually be found locally, one avoids paying expensive import taxes, and since the pump is a familiar technology to local pump and motor technicians, it can be serviced if problems arise. This is far easier than finding renewable energy technicians specializing in pico-hydro turbines. Furthermore, pumps are manufactured to operate under a wide range of conditions, are easy to install, and spare parts for these pumps are easy to find.
This is where the water flows into the system. It should be designed so that it remains clear of debris.
A metal or fabric mesh covering the intake such that material is blocked from entering the pipe.
A structure designed to divert the flow of water into the intake. It also maintains the level of the water at the intake,
If the stream is far away from the point of use, this diverts water a relatively large distance to the inlet of the penstock pipe. This component is not usually necessary, although if an irrigation channel is available, that may be used.
A basin located just before the penstock pipe that may serve as a settling basin to remove waterborne debris that may otherwise damage the turbine impeller over time. This part is probably unnecessary for most systems, as it is more difficult to build a forebay tank of adequate size than to replace the impeller in the turbine.
The Penstock Pipe
This vital piece of equipment serves to carry the water from the intake to the turbine.
This structure protects the turbine, generator, and electrical equipment. How big it is and where it is located depends upon the size of the equipment and the characteristics of the site.
This transforms the energy of falling water into mechanical energy.
This transforms mechanical energy into electrical energy.
A short, open canal that leads the water from the powerhouse back into the stream from which the water came. This may not be necessary if the turbine outlet is located near enough to the stream.
Pre-Feasibility Stage: Does a Pico-Hydro PAT System Make Sense for Me?
Given the right conditions, a centrifugal pump can be operated in reverse, acting as a turbine to provide electricity from falling water. If you are considering building a pump-as-turbine (PAT) system, the first step is to survey the resources that you have on site. To find the potential energy of water in a stream, it is necessary to know the volumetric flow of water and the available head. The head is the vertical distance the water falls, from the top of the decline to where the pump is installed, and is measured in meters. The volumetric flow is the volume of water, measured in liters, that flows past a point in a certain amount of time, measured in seconds. For example, a site may have a head of 50 meters and a volumetric flow of 15 liters per second. The minimum requirements for a pico-hydro PAT system are:
- Water that falls for most of the year
- A site located no more than 1 kilometers away from the point of use
- A head of at least 10 meters
- A volumetric flow of at least 10 liters per second
For more detailed instructions on how to tell whether your site is technically adequate for a pico-hydro PAT system, please read the “Site Assessment” section that follows.
Remember that although a system is feasible, it is still necessary to assess whether the project will be technically, economically, and socially sustainable. This may include assessing the community’s need for the system. How will the power be distributed and for what end-uses? Is there a trained technician in the area? What will be the role of community members? Men and women? How will the system affect the lives of all involved? These are just some of the questions that may arise when considering the implementation of a PAT system.
When assessing your site, the first question to ask is, “Does my site fulfill the minimum requirements?” Be sure to record any observations you make about your site during this assessment, as this information may help you in the future. Include worksheets for recording and organizing data?
How often does water flow in my stream or river?
In order for the hydro power system to be feasible, there should be flowing water for most of the year. Have you ever observed the stream not flowing? Does this occur often? If so, hydro power may not be your best option.
How far away is my point of use?
Look around for a steep section of stream within 1 km of your load. Look for waterfalls, as a sharper drop in elevation will minimize pipe length, and thus cost. It will also minimize the system’s ecological impact since waterfalls are already barriers to fish migration.
How far does the water fall?
For a pico-hydro power system, it is necessary for the head to be no less than 10 meters tall. When locating a site for your penstock pipe, or the distance over which water will fall, it is best to find a sharp drop in elevation so that water does not need to be conveyed a great distance in order to achieve a sufficient head. First, find a place no more than 1 km away from the load where the water flows steeply and measure the head here. You may even choose multiple sites and measure the head at each one. To measure the head using a level, you will need a sight-level, a stick of a known height (about 1 or 2 meters long), a calculator, and something to record your data.
- Stand the stick vertically at the proposed powerhouse location
- Place the level at the top of the stick and, with the level horizontal and pointed towards the hill, sight a straight line to a point on the hill. The difference in height between the first point and this second point is the height of the stick plus the width of the level.
- Record that you have measured one stick-length.
- Place the stick at this new location and repeat steps 1 and 3 here, remembering to record each time you measure a stick-length.
- Continue this procedure until you have reached the level of the water at the proposed intake site. This final measurement may be less than the height of the stick. If so, measure the part of the stick that represents this final height and write this down.
- Calculate the total head by multiplying the number of stick-lengths you measured by the length of the stick and adding on the final measurement:
Head = Number of Sticks x Length of Stick + Final Measurement
How much water is flowing?
One easy and accurate method of measuring the volumetric flow is called the bucket method. You will need a pipe, a 50 liter bucket, a calculator, and a stopwatch.
Use a pipe to divert all of the water into a bucket
Place the bucket at the end of the pipe and use the stopwatch to time how long it takes to fill the container.
Divide bucket volume (liters) by time it takes to fill bucket (seconds). The flow rate can be calculated with this equation:
Flow Rate = Bucket Volume / Time to Fill the Bucket
If it is difficult to divert the entire flow into a pipe, volumetric flow may also be found by the float method. For this, you will need to find a place in the stream with uniform width and flow, away from bends and large rocks. You will need a meter stick, string, an object that floats in water (a fruit, a hollow ball, a block of wood, a stick, etc.), a stop watch, and a calculator.
- Measure the width of the stream with the piece of string and measure the length of the string with the meter stick.
- Measure the depth of the stream in a few places with the meter stick. Use your measurements to calculate the average depth.
- Calculate the cross-sectional area (in square meters) by multiplying the stream width by the average depth. Write this down.
- Measure a length of one meter along the stream and mark either end of this meter with two small rocks or sticks. Find the water flow by putting the floating object into the stream at one end of the meter and timing how long it takes for the object to reach the other end. Divide 1 meter by the number of seconds this took. This will give you the flow in meters per second.
- Multiply the cross-sectional area (square meters) by flow (meters per second) to get the volumetric flow in cubic meters/second. Multiply by 1000 to get volumetric flow in liters/sec.
Remember: Water is life! Throughout the planning and construction of your PAT system, be aware of how you will be affecting the water resource and its availability to plants and animals. As a general rule of thumb, aim to use no more than 50% of dry-season flow to preserve ecology. Therefore, if you measured the flow to be the minimum 10 l/s, your system would use only 5 l/s. Use of a PAT for sites with less than 5 l/s flow is not recommended, as the turbine efficiency is likely to be low (below 50%).
Estimating Power Production
Once you have found a site that fulfills the basic requirements mentioned above, use the data you have collected to calculate an estimation of how much power your system will produce A rule of thumb in estimating power is:
Power (watts) = 5 x height (meters) x flow (liters/sec)
This number is only an approximation of how much power your system will produce, as it makes several assumptions. The actual system power will be determined by the type of pump you choose, the material, shape and size of the penstock pipe, and how the system is wired, among other factors. Compare your estimate to your estimate for the demand. Will the system meet the minimum demands of all the citizens of the community? Will the system size be larger than the demand, allowing for future expansion?
Once it has been determined that your site fulfills the most basic requirements of a pico-hydro PAT site, it is time to give some consideration to the system components and where they will be located. In this part, you will need to pay attention to the topography, geology, and vegetation already present at the site. These elements may put your system in the way of falling rocks, may cause you to have to make your penstock pipe unreasonably long, and may pose obstacles when transporting materials or during system construction. If the site planning is done with care, however, these elements may be utilized to support your system.
The most straightforward way to plan the layout is to begin at the ends – the weir and the powerhouse – and then to find the best path between them for the penstock pipe.
The weir is meant to raise the water level at the point where water enters the penstock pipe, and ensure a constant supply of water to the pipe. The weir should be sited so that:
- there are natural features to submerge the pipe, such as workable soil or low, heavy foliage.
- the weir will be protected from damage. Do not choose a site where the weir will be in the way of falling rocks or other debris. Also, think about how water will flow in the weir during floods.
- there are places to wedge in rocks and sandbags to form the weir, for example in a natural pool area near the lip of a drop. How the weir is built is explained in greater detail in the “Installation” section.
The powerhouse will be the structure that will house the system’s electrical equipment, and sometimes the pump as well. The powerhouse should be:
- located as low as possible to maximize the system head, and therefore the power produced.
- built above flood levels, for reasons of safety and accessibility. Water can sometimes rise 1 meter or more during a flood.
The Penstock Pipe
Once you have located the weir and the powerhouse sites, think about where the penstock could logically go between weir and powerhouse. Since the penstock is often the most expensive part of a pico-hydro system, it is important to minimize its length. Some key considerations when finding a site for the pipe:
- To minimize the pipe’s length, try to find a path such that the pipe parallels the stream.
- The penstock should be constantly pointing downwards, or else air pockets can form and cause pipe damage.
- Try to minimize the number of bends in the pipe, as well as how sharp these bends are. Many sharp bends will cause a great deal of head loss.
- If you choose to use a plastic pipe, either PE or uPVC, it will need to be buried to prevent UV degradation. Keep this in mind and try to find a path where it would be relatively easy to dig a trench.
- Think about what areas would need to be excavated. Where you can attach penstock to trees. Remember that trees grow… and fall down.
- As a general rule, pipe is more expensive and has higher losses than wire. Do what you can to minimize pipe length, even if it means a powerhouse father away needing a longer wire transmission line.
Once you have found a good route for the pipe, measure this length between the weir and powerhouse sites, including any bends that may be necessary to avoid trees or large rocks. This is about how much pipe you will need.
Final Recommendations for Site Assessment
- Take photos of everything! Make a map! It is important that you keep a record of your observations, considerations, and questions.
- Be open to several different options and discuss these with as many people as possible. Many minds and eyes can help find options that one might not find by oneself. Others familiar with the area may have a good sense of how much work excavation will take, which depends on soil type, or whether the selected site is stable or prone to landslides.
This section attempts to answer the question, “How much power will my system produce?”, as well as, “Which pump should I buy?” and “How big does my penstock pipe need to be?” There are many different ways to size a hydroelectric system. While many systems are sized according to the needs of the village, we will assume that you would like to extract the maximum amount of power possible.
To do so, you have been given a spreadsheet. The spreadsheet takes information that you have collected, such as head, volumetric flow, and pipe length, and gives you back calculated numbers you need to know, including system power and the sizes of some of your electrical equipment. More specifically, the spreadsheet will assist you with these four areas:
- Pipe Selection
- Pump Selection
- Capacitor Sizes and System Size
- Transmission Lines
The equations used to make this spreadsheet are not important, but should you want a technical explanation, take a look at “Pumps as Turbines: A User’s Guide” by Arthur Williams (ITDG Publishing 2003).
This portion of the spreadsheet asks for inputs of:
- Pipe Diameter in inches
- Pipe Length in meters
- Volumetric Flow in liters per second
- Head in meters
- The Coefficient of Flow
- Types of fittings and how many of each
Inputs 2-4 you have already measured and can type those in now. Be sure that your measurements have the correct units. Remember that your volumetric flow should be about half of the dry-season flow. The coefficient of flow is a number determined by which material you choose for your penstock pipe and does not have any units. The material you choose will depend upon what is available locally, the pressure the pipe will experience, how the pipe will be transported, and how the sections of pipe will be joined to one another.
Your three main pipe material choices are uPVC, polyethelyne (PE), and steel. Steel pipe is usually more available than plastic pipe, but is heavier and will be more difficult and costly to transport and install. PE pipe, on the other hand, is light and flexible, but difficult to join together. We recommend that you use uPVC pipe since it is strong, readily available, easy to work with, and inexpensive. For these reasons, we will focus the “Installation” section on uPVC pipe.
Some calculations require that you know how many fittings you will use and of which type. If you do not know exactly, these numbers may be estimated. There are many types of fittings, each with its own shape and affect on how fast the water flows. For help identifying which fittings you have, refer to the images below and enter an estimate of how many fittings of each type you will need:
Outputs in this section of the spreadsheet include:
- Pipe diameter in meters
- Hydraulic Radius in meters
- Pipe Head Loss in meters
- Hydraulic Gradient (unitless)
- Pipe velocity in meters per second
- Head Loss In Fittings
- Total Head Loss
- Head Loss Ratio
The pipe’s diameter D, the Volumetric Flow Q, the pipe length L, and the coefficient of flow C all determine the amount of energy lost in the pipe due to friction in the Hazen-Williams equation:
This energy loss is called the head loss because this loss in energy may be viewed as if the system had lost some of its height. Pipe head loss is due only to friction in the pipe, head loss in fittings is due to friction and changes in pipe size at the pipe fittings, and total head loss is a sum of both these losses.
Input 1, the pipe diameter, will be adjusted until the desired head loss ratio (total head loss divided by total head) is achieved. This value should never be more than 33%, otherwise an increase in flow will result in a decrease in power. It is most economical to allow a head loss ratio between 10% and 20%. If the head loss ratio is greater than 20%, then too much energy is being lost by friction and a larger diameter pipe should be selected. If the head loss ratio is less than 10%, then it may be wise to select a smaller diameter pipe because it will cost less. A larger diameter will decrease the head loss ratio, whereas a smaller diameter will increase it.
Each pump on the market has certain values for maximum efficiency, voltage, frequency, rpm, and more. These can usually be found on the label or on a document from the manufacturer. In addition, each pump has values of head and flow at which it operates best. When the pump is operating under these conditions, it is operating at its maximum efficiency and is said to be at the best efficiency point (BEP). As you have already found, your PAT site has a specific head and volumetric flow. These values are different from the BEP values for the pump when it is operated as a pump. Both the optimal head and flow will be greater when the pump is operated as a turbine to make up for energy losses. A more detailed explanation and practical advice can be found in the book referenced below .
This section of the spreadsheet calculates the best efficiency point head and flow for a pump that will fit your site. Simply use this spreadsheet to find the best efficiency flow and best efficiency head, and find a centrifugal pump that matches these numbers more or less.
The only inputs you will have to provide for this section are:
- Turbine (Pump) Efficiency
- Generator (Motor) Efficiency
Both of these values should be made available by the manufacturer. If they are not, some good estimates are 78% turbine efficiency and 77% generator efficiency.
From these data and the data from the Pipe Selection section, your spreadsheet calculates the following:
- Effective Head in meters
- Ideal Jet Velocity in meters per second
- Jet Power in watts
- Best Efficiency Pump Flow in liters per second
- Best Efficiency Pump Flow in liters per minute
- Best Efficiency Head in meters
- Estimated Power Output in kilowatts
- Price in Bhat
Effective head is another term for usable head, or the part that results in useful power once the head losses are taken into account. Effective head, ideal jet velocity, jet power, pump flow in liters per minute, and power output are all specifications that will help you to choose a pump that is appropriate for your site. Once you have calculated these numbers, write them down and bring them with you when looking for a pump. Centrifugal pumps are most easily located in large cities and you may find them in the yellow pages. Because of their use in agriculture, pumps are also widely available in small agricultural towns.
When looking for a pump, select a mechanically-sealed end-suction unit with 3 phase motor. A pump-motor unit makes it possible to avoid a belt drive, reduces energy losses, is easier to install, costs less, and lasts longer than a system with a belt drive. Most pumps, even for powers of less than 1 kW, are supplied with three-phase induction motors. Fortunately, it is possible to use a three-phase induction motor as a single-phase generator and this is the preferred approach to providing a single-phase supply.
Standard centrifugal pumps are normally offered with the option of a 2-pole or 4-pole motor. 6-pole motors are available, but are more expensive. For a 2-pole motor, the running speed is about 3000rpm, while a 4-pole motor runs at about 1500 rpm. A pump designed for 1500 rpm rather than 3000 rpm is preferable because the slower rotation results in less bearing wear. However, if a 1500 rpm pump cannot be found, 3000 rpm also works. This pump should also have an IP rating of 4 or 5. The IP rating is a measure of how waterproof the motor is, with 4 or higher being protected from sprays in all directions with limited infiltration.
Capacitor Selection and System Size
Induction generators require a magnetic flux to start. This may be established by a capacitor bank connected to the machine. To start up a three-phase induction generator with a single-phase output, one may use three capacitors in a C-2C connection. This wiring configuration allows for self-excitation and ensures balanced single-phase generation from the three-phase induction machine. In a C-2C connection, the load is connected to one phase, while the currents of the generator are balanced (for one particular value of load). For the C-2C connection, the induction generator must be connected for 220/240 V delta, if this is the single-phase voltage required.
The size of the capacitors determines the voltage and speed at which the generator will run. Further information on the sizing of capacitors for a PAT system is given in Motors as Generators for Micro-hydro Power by N Smith. To size your capacitors, refer to the Capacitor Selection section of your spreadsheet. The inputs are:
- Motor Rated Power in kilowatts
- Motor Frequency in hertz
- Rated Current in amps
- Rated Voltage in volts
- Rated Speed in rpm
- Power Factor
Values 1-5 can be found on the pump unit’s label. The power factor can be assumed to be 0.82.
The outputs in this section are:
- Apparent Power in VAs
- Real Power in watts
- Reactive Power in VARs
- Reactive Power per Phase in VARs
- Capacitor Current in amps
- Capacitor #1 Size in micro-farads
- Capacitor #2 Size in micro-farads
- Optimal System Power for Balanced Phases in watts
- Motor Current Derated 80% in amps Why? I might need to look at the ‘motors as generators’ book to answer this. My guess is that you generally want to avoid running motors at full rated current – because of higher temperatures encountered in the field, etc.
- Motor Current for Balanced Operation in amps
The C-2C arrangement is composed of three capacitors, each of the same size. One capacitor (C) is wired by itself, while the other two (2C) are wired in parallel to one another. When two capacitors are wired together in parallel, the total capacitance is the sum of each capacitance. This is why on your spreadsheet 2C is twice C. When purchasing capacitors, use motor run, and not motor start capacitors because motor run are designed for continuous duty.
There are many ways to control the electrical output of your system. One successful method we have found is to use an electronic load controller (ELC). This type of control keeps the load on the generator constant by diverting spare capacity into ballast loads in order to allow other loads to be switched on or off. If used with an induction generator, only a single controller known as an induction generator controller is required. The ballast loads must be purely resistive, and can be used for space heating, electric drying, or water heating. These loads may need to be located near to the controller to eliminate interference interference to medium and long wave radio reception. The best load we’ve found so far is a resistive heating element, though incandescent light bulbs are cheaper. At Mae Wei, we used a Leonics ELC, which is rated at 500 watts and can be connected in parallel. Any specifications for the ELC?
Single-phase transmission has the advantage of not needing the loads to be split into three equal parts, which may be difficult. While three-phase distribution is required to run motors or other inductive loads, if you only require electricity for resistive loads, then single-phase transmission is the way to go.
In this section of the spreadsheet, the inputs are:
- One-Way Wiring Distance in feet
- Acceptable %Voltage Drop
- Wire Coefficient
For input 1, measure the wiring distance from the PAT system to the point of use. This should be about half the total wire length. For input 2, an acceptable voltage drop is anywhere between 2% and 4% at typical load, with a lower percentage being better. The wire coefficient depends upon the wire material and is used in calculating the wire’s size from the Voltage Drop Index.
The outputs you will be given are:
- Voltage Drop Index (unitless)
- Wire Area in mm2
- Wire Gauge in American Wire Gauge (AWG) units
It is generally recommended to use aluminum wire for the transmission lines because it is cheaper, lighter, and carries high voltage electricity better than copper. Copper wire is the best type to use in homes because it is more conductive and stronger. Whichever type you use, be sure that the insulation is rated for UV exposure.
You’ll want to show some photos of how actually to mount the wires on the insulators on the poles. We typically install a knife-switch cut out AFTER the controller and BEFORE the transmission line AT THE POWER HOUSE in order to disconnect the village and transmission line at power house — to, say, do repairs on the transmission line if there’s a landslide or something. And again another knife switch at the distribution point at the village end of the transmission. This way power can be cut off from the village for whatever reason.
If you want to leave the system turned off for a few hours or longer, go up to the mirco-hydro and turn off the water supply to save wear and tear on the turbine.
Now for the exciting part: Let’s get building!
Even the best-designed PAT system will not perform well if it is not properly installed. Care must be given to
the proper installation of all of the items included in the system.
Preparation and Supplies
Before you begin installing, there are some basic tools that you will need:
- Two or more walkie talkies for long-distance communication and coordination among teams. We suggest the Motorola Talkabout, which is good for a range of about one kilometer.
- Some pens and paper to write notes and record parts needed to buy, reminder notes, etc.
- Hacksaws to cut PVC pipe
- Multimeter to measure current and voltage
- Screwdrivers for electrical equipment
Building a micro-hydro power system requires the help of many hands and heads. There are so many things to be done, from digging a trench for the pipe to putting the roof on the powerhouse, that the whole village could be involved! We generally do these project with four teams, each led by someone with a pretty good sense of how to build that part. For example, someone who has had experience with building irrigation systems could be in charge of the weir or penstock teams, while an electrician would be perfect to lead the transmission line and wiring team. Teams of six people or more people could be divided into tasks:
- transmission line and wiring
Each team should be encouraged to complete the task at hand using their own problem-solving along the way. At least once during each workday, the teams should check in with one another to discuss their progress and any problems they may have run into. It is amazing how much we can solve by putting our minds together!
It may be necessary to clear a path to help with transporting materials to the site, especially large components, such as sections of the pipe. This may involve clearing brush and rocks, or even digging steps into the earth and tying ropes for dangerously steep sections.
The weir should be built so that it serves its purpose of diverting water into the pipe, but does not need to be built for permanence. It should be made out of local materials and with local technology so that, in the case it is damaged in a flood or storm, it is easily repairable. If people in your village have built weirs for irrigation, follow this same process for building the pico-hydro power weir. For materials, look around for what there is. Use anything that will help to block the water. This may include:
- Woven nylon fiber bags filled with sand
When building the weir, remember that some leakage is OK because it allows water to stay in the stream for the health of the ecosystem. The plants, animals, and other living things in the region of the stream along the pipe will be less affected if allowed to keep using some of the water. Your weir should also be built so that it can be flushed out periodically from sediment buildup. This may be achieved by making a hole towards the bottom of the weir and piling sandbags in front when you want to plug the hole, removing them when you want to clear out the sediment.
Penstock Inlet and Filters
The inlet of the pipe should be located at or slightly before the weir and requires a filter so that debris do not travel down the pipe and damage the turbine.
To build the filter…big bamboo filter — the size of a beach ball or so — around the inlet to the pipe. Big is good because it provides more surface area so that you don’t get shut down by leaves clogging.
A 90 degree elbow not glued in, combined with a short section of pipe makes a nice ‘snorkel valve’. Tilt it sideways or downwards into the water normally. Tilt it upwards so that it’s sucking air when you want to shut off water supply. This is useful during construction to keep the penstock dry until final commissioning. Don’t suddenly cover the inlet with a watertight cover — it’ll collapse the pipe!!!
Make filters upstream to catch floating sticks and leaves. These can be made by driving sections of bamboo or wood vertically into the stream bed combined with a horizontal cross-stream piece or two. Then use smaller slats to make a rough filter (http://www.flickr.com/photos/bget_tak/2270076157/in/set-72157603911290812/ is not a great picture, but you get the idea). If you fear big stuff coming down the stream (logs) during floods, then make a barrier to protect the intake. This could be a large metal culvert or a metal cage, filled with rocks to make it strong and heavy.
As we mentioned earlier, it is important to avoid sharp bends in the pipe. Gentle bends can be accomplished by bending the straight pipe over the course of 50 meters or so. PVC pipe is generally purchased in 4-meter sections. Sections should usually be glued together, especially if the pipe is buried, as it would take a lot of work to dig up again later. However, if the pipe exists in an area where there have been many landslides, it is better for the pipe to come apart than for it to break, which would require an expensive, time-consuming trip to the hardware store.
The penstock pipe must be able to withstand the pressure of the water flowing through it. To measure how it stands up to pressure, PVC pipe comes in classes. As rule of thumb, take the ‘class’ (e.g. 5 or 8) and multiply by 10 to get the static pressure in meters it can hold without rupturing. For example, class 5 pipe is good to a static pressure of 50 meters head. Class 8 to eighty meters. Pipes of higher classes have thicker walls and thus they are more expensive. Because of possible dynamic surges in pressure, called water-hammer, we design conservatively by always overestimating the class we will need. For example, if your system has a head of 35 meters, you should buy pipe sections of class 4 or 5. It is also possible to purchase sections of different classes and to use the higher class sections closer to the the powerhouse, where pressure is greater. This will save money since the pipes of higher classes are more expensive.
When purchasing pipe:
- Be sure to purchase a type of pipe with ‘bell ends’ that does not require many couplings
- Always check the pipe and joints for leaks before buying
PVC degrades in the sunlight, so it will need to be buried. Before burying the pipe, the team responsible for installing it will need to dig a trench in the soil, about six inches deeper than the diameter of the pipe. Make sure that the floor of the trench sloped downwards at all points so that water will run downhill throughout the pipe.
If the ground is unmanageable and the pipe cannot be buried, it may be covered it with soil or bamboo above-ground instead. This will not offer as much protection, but is the next best option.
In areas where it is above-ground, the penstock may need to be attached to trees for support. A good way is to screw a 1/4″ or 3/8″ x 3″ lag bolt into the tree. Then wire the penstock to the lag bolt. A lag bolt is like a screw, but bigger — use a wrench to screw it in. This is better than wiring the penstock to the tree directly because if you wire around the bark of a tree you’ll choke it and kill it. (The life of a tree is in the inner bark tissue).
If you have to make sharper bends, try to use ‘sweeps’ rather than ‘elbows’ to reduce friction. Where the penstock enters the powerhouse, you’ll generally have to do some angle-changing to get it to line up with the inlet to your turbine. I find that you can get any angle you need if you have two 45 degree elbows (or sweeps) joined together (See Figure 10 on HKT report i emailed you).
A reducer is usually required where the pipe meets the PAT because the penstock pipe diameter is usually greater than the diameter of the pump’s outlet pipe. This is because the flow for operating the pump as a turbine is greater than the flow if it was operated as a pump. The penstock diameter (typically 4″ or 6″) should be reduced to about 2” down to the turbine inlet diameter (often 2″ or so).
Install a screw-type valve (that takes several turns or more to close) just before the turbine inlet. Keep this valve open during construction so that if someone makes a mistake up at the weir and sends down water, it won’t cause an exploded pipe and a flooded powerhouse (see Figure 13 in the HKT report that i emailed you for a photo of this happening). If you glue a mistake, it’s possible (though difficult) to pull the pieces apart by building a small fire and heating the pipe and prying it apart. Keep in mind that PVC glue is carcinogenic. Use a brush rather than your finger to apply. Wash hands before eating. Try to ensure good ventilation.
The powerhouse should be built to be waterproof, as it will house the electrical equipment, including the electronic load control, capacitors, switches, and meters. To build the powerhouse, first clear the selected area of all vegetation and large rocks. You can generally pour a concrete foundation for the whole powerhouse. To save concrete, it is possible to make a smaller concrete pad about 1m x 1m x 6” to put the turbine on. You’ll need to bolt the turbine to the floor so that it doesn’t move around. To do so, you may use six-inch J-shaped bolts as tie-downs. You may also use bolts with washers embedded in the concrete to keep them from being pulled up. To do this, obtain a steel plate (about 8” x 8” x 1/4″ thick or so) with holes for the bolts fabricated for the turbine to sit on. This way the bolts are guaranteed to line up right and won’t settle funny and dry crooked in the concrete (See slides 8 to 11 in attached power point).
The frame of the powerhouse may be constructed from local wood, using vertical poles at the corners. You may use bamboo or corrugated metal for the walls. The roof may be constructed out of corrugated metal, with any holes sealed so that the interior remains dry during the rain. The powerhouse should be built about 10′ x 10′ x 6′.
Inside the power house, you will install the electrical equipment, some of which will require assembly first. The pump is connected directly to the capacitor box assembly.
To fabricate the C-2C capacitor assembly, follow the wiring diagram. You have three capacitors, all of the same size. You will wire two of these in parallel, and one separately, to different phases of the motor. These capacitors may be placed in a box, but should not be completely enclosed, as this may result in overheating. for greater ventilation, the capacitors may also be wired in the open air, mounted (to what?) with zip ties. The capacitors can be expected to last a year or so.
The capacitors are then connected to an ammeter in series and a volt meter in parallel, as in the wiring diagram. These help with the important task of monitoring the voltage and current of your system. Fabricate an assembly that includes voltmeter, ammeter and (optional) indicator light, which tells you when the system is at safe current and voltage levels.
The meters are then connected to the electronic load controller, which is connected to the ballast load. As mentioned before, the electronic load controller (ELC) keeps the load on the generator constant.
Fabricate another box for knife-switches (see slide 1 in Mae Wei designJan08 powerpoint for diagram
The Transmission Line
The transmission lines carry electricity from your PAT system to wherever it is needed. The lines will need to be run off the ground, high enough so that they will not be hit by falling branches. String the wires on long wooden poles sunk into holes in the ground. These holes may be backfilled with rocks and soil. Using wooden poles is advantageous because they are found locally, but the wood rots fast. For this reason, concrete poles make a good alternative. Be sure to attach the wires to the poles in a way that will not cut into the wires.
Once everything is in place, it is of utmost importance that the wiring is checked and rechecked. Poor wiring may damage the system or, more importantly, put someone in danger. This includes wiring in the powerhouse, transmission lines, and in the village. After this is done, close the water valve down at the powerhouse and slowly let the water into the intake above. This part must be done very slowly so that the pipe is not damaged. When pipe is full, fully submerge the inlet pipe. Then, down at the powerhouse open the valve and the turbine should spin up to speed.
If the turbine is spinning but is not generating electricity, you’ll need to magnetize the rotor. New motors generally don’t have any residual magnetism in the rotor, so this may only need to be done once. To magnetize the rotor, short-circuit a 6 or 12-volt battery across any two of the three delta motor terminals. This current will induce a magnetic field in the rotor, which will leave a bit of residual magnetism. Turn on the water again — after a few seconds (it might take even 20 or 30 seconds) the voltage will exponentially build and the lights will come on. You may need to re-magnetize in the event of a short-circuit fault.
When you turn it on, voltage should rise first. Once it hits 230 volts, then the controller kicks in and holds voltage constant while current rises. Test pico-hydro by fully opening the valve. Power production is (ignoring power factor) voltage times current.
If the turbine is running. your volt meters and ammeters are showing that you are producing power, and the wiring is in place, then it is time to turn on some loads to see that everything is working well on the village end of things. If your lights and appliances turn on, then congratulations! You have successfully completed the installation of your PAT system. It’s time for a celebration!
Now that you have successfully installed your PAT system, you need to know how to care for it so that it keeps working as well as possible. The long-term maintenance and operation of your system consists of minimizing wear on the moving parts, keeping the pipe free of debris, and managing the financial and technical sustainability of your system.
Managing Energy Supply
If the total village load, or how much power is required when all appliances are turned on, is much smaller than what the system produces, you may turn down the water supply. Turn it down so that voltage is still at 230, but current is reduced to be slightly more than is required by the max load. Do not decrease the water flow too much, or there may not be enough power for everyone’s needs. Turning down the water reduces wear and tear on the turbine and keeps more water in the stream. As the load grows over time, you may increase the flow of water. Any adjustments to water flow should be made, by turning the water valve above the micro hydro turbine slowly to avoid a water hammer surge.
Once you’ve observed the maximum power your system produces, you know about how much load can be powered. It is important that someone manages the load side of the system and that he or she pays attention to load growth from the first day. As a general rule, rice cookers should be prohibited since they use so much electricity. Since they are usually used at night, they compete with power for lights. Additionally, you will get the most use out of your system if the power is used as much as possible during all times of day. Since much of the power will be needed for lighting at night, some end uses may need to be shifted to the daytime.
If you’re going to be providing electricity to households, consider using mini-circuit breakers to limit current to each house to avoid a common-property problem in which individual household consume more than their share. To manage this, begin by having a village meeting to decide what this amount is. You may supply a certain amount of power to a household per person, per adult, on a need-basis, or based on how much was paid by that household. If the wattage is exceeded, the circuit-breaker will switch off all power to that household. They need only turn off all appliances and switch the circuit-breaker back on to regain power.
If in the future the energy demand exceeds the maximum energy generated by the system, a second turbine can be added 30 meters below the turbine outflow to add capacity.
To maintain the system, it is very important that there be some money set aside to buy extra parts and to pay people who clean or repair the system. As mentioned in the previous section, you may work with everyone in the village to set up a pot of money that grows over time to cover repairs and upgrades. This may be done by setting up fee a system in which each person using electricity from the PAT system contributes some money. This may be based upon their ability to pay,
If the cost of micro hydro is too high for some people, the financial cost can be reduced by contributions of labor. Increasing the number of people involved in a scheme can reduce the cost to everyone when micro hydro schemes exhibit economies of scale.
To keep the system running, designate one or more technically competent people to operate the system. These people should have a good understanding of how the system works, how to turn on and off the water safely, and how to read and interpret the voltmeters and ammeters.
It should be made clear to those not in charge of the system upkeep that they are not to tamper with the system in any way. Signs in the power house, or near the pump, transmission lines, and any other accessible component will help to remind people that the system is important, fragile, and potentially dangerous.
Besides operation, it is important that some people be in charge of system maintenance. These people may be in charge of cleaning, monitoring, and repairing the electrical equipment, pump, and civil works in the case of damage. They may also be responsible for replacing parts as they fail. Some of these maintenance tasks include:
- Cleaning out the weir when it fills with silt
- Cleaning the screen over the intake pipe at least once a week
- Monitoring erosion from the turbine outflow and remedying this as necessary
- Replacing bearings wen they wear out
- Replacing capacitors when they burn up
These are just some of the many tasks a system maintenance person could be presented with. These may be divided among many people if necessary.
Glossary of Terms
Electronic Load Controller