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A pelton water turbine or Pelton wheel is a type of hydro turbine (specifically an impulse turbine) used frequently in hydroelectric plants. These turbines are generally used for sites with heads greater than 300 meters. This type of turbine was created during the gold rush in 1880 by Lester Pelton The water in a Pelton turbine is moving quickly (high velocity head, figure 2) and the turbine extracts energy from the water by slowing the water down, which makes this an impulse turbine.
When used for generating electricity, there is usually a water reservoir located at some height above the Pelton turbine. The water then flows through the penstock to specialized nozzles that introduce pressurized water to the turbine. To prevent irregularities in pressure, the penstock is fitted with a surge tank that absorbs sudden fluctuations in water that could alter the pressure. Unlike other types of turbines which are reaction turbines, the Pelton turbine is known as an impulse turbine. This simply means that instead of moving as a result of a reaction force, water creates some impulse on the turbine to get it to move.
pelton turbine for sale
Pelton water turbine
Figure 2. A nozzle turns hydraulic head into a high velocity (with high velocity head) stream of water which hits the Pelton turbine and makes it spin. The water coming out the bottom has very little energy left.
The Pelton turbine has a fairly simplistic design. A large circular disk is mounted on some sort of rotating shaft known as a rotor. Mounted on this circular disk are cup shaped blades known as buckets evenly spaced around the entire wheel. Generally, the buckets are arranged in pairs around the rim. Then nozzles are arranged the wheel and serve the purpose of introducing water to the turbine. Jets of water emerge from these nozzles, tangential to the wheel of the turbine. This causes the turbine to spin as a result of the impact of the water jets on the buckets.
The operation of a Pelton turbine is fairly simple. In this type of turbine, high speed jets of water emerge from the nozzles that surround the turbine. These nozzles are arranged so the water jet will hit the buckets at splitters, the center of the bucket where the water jet is divided into two streams. The two separate streams then flow along the inner curve of the bucket and leave in the opposite direction that it came in. This change in momentum of the water creates an impulse on the blades of the turbine, generating torque and rotation in the turbine.
The high speed water jets are created by pushing high pressure water (such as water falling from high heads) through nozzles at atmospheric pressure. The maximum output is obtained from a Pelton turbine when the impulse obtained by the blades is maximum, meaning that the water stream is deflected exactly opposite to the direction at which it strikes the buckets at. As well, the efficiency of these wheels is highest when the speed of the movement of the cups is half of the speed of the water jet
Pelton turbines are used on medium to high head hydropower sites with heads from 20 metres up to hundreds of metres.
Power outputs can range from a few kW up to tens of MW’s on the largest utility-scale Pelton systems. Because the operating head is high, the flow rate tends to be low, ranging from 5 litres/second on the smallest systems up to 1 m3/s on larger systems. The relatively low operating flow rate is not a problem because the terrain required to achieve the heads must be hilly or even mountainous, and these are typically high-up in a river catchment so the catchment area, and hence flow rate, is small.
Compared to the power produced Pelton turbines are relatively compact, and because the flow rates are relatively low the associated pipework is relatively small. This means that a Pelton turbine itself is generally easier to install than an equivalently-powered Kaplan turbine, but Pelton turbines need a high pressure water supply from a penstock pipe, and designing and installing the penstock pipe is normally more challenging and is more expensive than the turbine.
A basic diagram of a Pelton turbine is shown in Figure 1, and a rotor (this is the so-called ‘Pelton wheel’) is shown in Figure 2.
Diagram of Pelton turbine main parts
In Figure 1 the penstock pipe delivers the water on the left-hand side. Before it enters the turbine it passes through the nozzle or spear-jet (a spear-jet being an adjustable nozzle). The spear-jet adjusts the flow rate through the turbine by moving back and forth which moves the head of the spear into and away from the nozzle, varying the flow area and therefore the flow rate. The position of the spear-jet is normally controlled by the system controller in response to changes in water level (hence flow rate in the river) at the intake.
The nozzle in a spear-jet is subjected to a constant high-pressure water flow and can erode over time, especially if there is a higher than normal concentration of abrasive sands in the water. For this reason it is normally made from tungsten carbide which is incredibly hard and able to resist erosion, and even then is designed to be easily replaceable during servicing.
Figure 2 – ‘Pelton wheel’ rotor (note two different rotors shown)
Once through the spear-jet the water impinges on the rotor and transfers around 97% of its kinetic energy into the rotational energy of the rotor. To achieve this transfer of energy the buckets are precisely designed to minimise all losses. Firstly the ‘splitter’ splits the jet of water into two equal halves for each side of the bucket, then the shape of the bucket is carefully designed to turn the jet of water almost 180 degrees to transfer the kinetic energy with the minimal amount of splashing and leave just enough energy for the water jet to fully exit the rotor so that hardly any water hits the next bucket, causing drag. The surface of the buckets is normally highly polished to minimise drag and the rotor itself is finely balanced. The small ‘cut-out’ in the tip of the bucket is to ensure that the next bucket doesn’t cut through the jet of water on the previous bucket prematurely as the rotor rotates.
Once the water jet leaves the rotor it falls to bottom of the turbine casing and returns to the river through a discharge pipe.
To get a higher flow rate, hence more power through a single pelton rotor it is possible to have multiple spear-jets, as shown in Figure 3. Six jets is normally considered to be the maximum, and with this number of jets the turbine casing design becomes critical to ensure that the discharge water clears the rotor and can leave the rotor area without splashing around all over the place and causing excessive drag.
Figure 3 – A six-spear-jet Pelton turbine
Pelton turbines can reach up to 95% efficiency, and even on ‘micro’ scale systems 90% peak efficiency is achievable. Also the efficiency is maintained at a high level even for part-flow rates, mainly because of the low-loss design of the spear-jet. On multiple spear-jet Peltons it is possible to operate at very high efficiencies from just a few percent of the maximum flow rate all of the way up to the maximum. A typical efficiency curve for a single and twin spear-jet Pelton turbine is shown in Figure 4; with more spear-jets the Pelton turbine would operate at high efficiency over an even wider flow range.
Figure 4 – Efficiency curve for a single and twin spear-jet Pelton turbine
Pelton turbines rotate at relatively high speeds, so it is often possible to design them so that the optimum operating speed of the turbine and generator are the same so they can be directly coupled. This has the advantage of reducing the cost of the drive system because just a flexible coupling is required and saving all of the losses in the belt-drive or gearbox which can be between 2% to 7%.
Figure 5 – Twin spear-jet Pelton turbine installed by Renewables First in 2007
Figures 5 below shows a Pelton turbine with twin spear-jets installed by Renewables First in 2007. This system has a maximum power output of 11 kW, so is a relatively small system. Figure 6 shows a large multi-megawatt system being installed (not by us), but gives a good idea of how large Pelton systems can be. This system has twin rotors and a directly-coupled generator shown in the right of the picture.
Domestic Wind Turbines – The Basics
Households can now make use of wind power technology by installing micro turbines, also known as or small-wind or ‘microwind’ turbines. When the wind is strong enough it turns the blades of the turbine, generating electricity. The U.K. climate is ideal for wind harnessing technologies as 40% of the wind in Europe is experienced here, and in the right area you should be able to see substantial savings on your electricity bills.
There are two types of microwind turbine:
- Building mounted: These systems are installed on your roof, and have a fairly small capacity, averaging 1-2kW
- Pole mounted: These installations are freestanding and have a larger capacity of around 5kW-6kW
The Energy Saving Trust has calculated that in an ideal location a roof mounted micro-turbine system could reduce your electricity bills by around £350 a year. Your system could also be eligible to receive payments for the electricity you generate through the government’s Feed-In Tariff (FIT) scheme. Here’s how the scheme works:
- You are paid a ‘Generation Tariff’ for each unit of electricity you generate, regardless of whether you use it or not, at a tariff rate that is fixed when you make an application for the scheme. The scheme then pays you starting from when you apply to the scheme, for 20 years. A pole mounted installation in an ideal location could receive £2,700 a year at current tariff values.
- You are also paid an ‘Export Tariff’ for any generated electricity that you don’t use. The same pole mounted installation could receive £160 a year in export payments at current tariff values.
- The electricity that you generate is free for you to use. If you use more electricity than your system is generating at any point you will be taking it automatically from the grid as you do now, which you will pay for. Overall, however, you will still save money on your electricity bill.
- You can get a loan to cover the cost of installing your system by instead signing up to the Green Deal scheme. The loan is recovered via your energy bill, using the money you have saved on your energy bill by using the system. This means that the installation should not cost you any additional money.
pelton wheel turbine working principle
How Domestic Wind Turbines Work
- When the wind turns a wind turbine’s blades this movement drives the rotating shaft the blades are attached to. This shaft sits inside a generator. Inside the generator the shaft is surrounded by a magnetic field, so that when the shaft rotates it generates an electric current. In smaller turbines the blades can be attached directly to a generator with a magnetic field.
- The electricity the turbine produces is DC electricity. This DC electricity passes through a device called an inverter, which connects the turbine and your home’s electrical system. It converts the DC electricity to AC electricity which can be used in your home.
- The electricity the wind turbine generates can be fed directly into your home or stored in batteries. The turbines can be connected to the national grid so that you can export any surplus electricity and receive FIT payments for your electricity, or you can keep your turbine off the grid and store your surplus using batteries, though this arrangement won’t qualify for FIT payments.
- If your turbine is connected to the grid, any surplus electricity is automatically exported to the grid, and if you use electricity from the grid this is also supplied to your system automatically.
The providers of the FIT scheme do not currently measure how many units of electricity you export, but for microwind turbine systems it is assumed to be 75% of the electricity you generate. The capacity of a microwind turbine system to generate electricity varies according to the individual system, and can be described in kilowatts (kW). This value can range from approximately 0 to 15. The average capacity of a house mounted system is 1-2kW and the average capacity of a pole mounted system is 5-6kW.
Whilst this measure is valuable, it does not fully describe the capacity of a turbine as the wind speeds at which this capacity is reached differ from turbine to turbine. This means that the Small Wind Turbine Performance and Safety Standard is also used. Contained within this standard is the BWEA Reference Annual Energy. This is the energy in kWh that the turbine will produce annually at a consistent wind speed of 5m/s at a set turbine height. A second value, the BWEA Reference Sound Levels give the noise level of the turbine from 25 and 60m away rounded up to the nearest decibel (dB).
Installing Microwind Turbines
When considering a microwind turbine installation it is essential that you accurately measure the wind speed of your specific location. The average annual wind speed required to make wind turbines worth the investment is a minimum of 5 metres per second (11 mph), which is not usually achieved in urban or suburban areas. This is because the wind speed in urbanised areas is usually reduced by by closely arranged buildings and trees. Nearby hills can also affect wind speed, as does whether you live in a valley or not.
It is strongly recommended that before you commission a microwind installation that you accurately measure your local wind speed by buying and fitting an anemometer (wind measuring instrument). You should leave this device to carry out measurements for at least three months but ideally you should leave it for a year to get a comprehensive overview of the wind levels your property is exposed to.
Domestic Wind Turbine Installation Checklist
There are a few important things to consider:
- Building mounted or pole mounted: Building mounted systems have a lower capacity than pole mounted systems, meaning that they will generate less electricity and are cheaper to install
- Whether you want to connect to the grid: Currently you will need to connect to the grid toreceive FIT payments. Contact your local DNO (District Network Operator) to arrange connecting your turbine to the grid
- Whether your local area is prone to power cuts: When the power in an area fails all inverters connected to the grid are switched off, meaning that your system will stop working. You can install batteries with your turbine to provide a back-up electricity store – ask your installer for more information
- Roof integrity: If you are intending to install a building mounted turbine it’s wise to consult your installer on whether your house is durable enough to support the turbine – they can be heavy and vibrate when in use
- Planning permission: There are currently permitted development rights granted for domestic wind turbine systems in England, which should mean that you won’t need planning permission for your installation. However, the criteria for this are complex and there are varying needs for planning permission across the rest of the U.K. It is therefore wise to check the planning permissions for your installation with your local authority well in advance. You will have to supply a number of documents as well as paying an application fee of £150. It is a good idea to meet with a local planning officer before submitting your application so you know exactly what is required, as is consulting with any third parties such as neighbours who may be affected by your installation. Some installers will provide information and support with filling out planning applications
- Environmental permissions: If your planned turbine is over 15m tall or you are planning to install two turbines you may be required to commission a bat or bird survey of the area
- Your energy supplier: The larger energy companies have a legal obligation to be registered FIT suppliers but for smaller companies this is optional. Check with your energy supplier to see what they provide regarding FIT
- Are you carrying out other building projects? You might be able to reduce the size of your installation bill by carrying out the work at the same time as any other building or landscaping work you are planning
The time your system will take to install will vary with your specific circumstances, particularly if you decide to carry out the installation at the same time as other building work.
Domestic Wind Turbine Installers
If you intend to apply to the FIT payments scheme you will need to ensure that your installation is carried out by an MCS accredited installer using parts that meet MCS standards. When your installer signs off your installation as being MCS compliant they will give you an MCS certificate that you will need when applying for the scheme. If you are financing your installation through the Green Deal you will need to instead use an authorised Green Deal installer.
Domestic Wind Turbine Costs
A standard 1kW building mounted turbine installation costs around £2000, with a 2.5kW turbine costing around £15,000 and a 6kW around £23,000 including installation costs.
Typically larger systems cost more to install but can generate more electricity, delivering you bigger energy savings and larger tariff payments. An average system working in a 5 m/s wind speed location can save you around £350 on your electricity bill and pay you £160 in Export Tariff payments and £2,700 in Generation Tariff payments every year. You will be paid these tariffs from the date you register for FIT payments for 20 years.
The system will run for at least 20 years, and as the tariff value is set at the start of payments and index linked it is likely that the system will pay for itself in 7 years or less. After this point you will be receiving savings on your electricity bills and payments for around 13 years. For more information on the FIT scheme you can visit our Feed-In Tariff (FIT) page.
If you cannot afford to pay for the installation yourself the Green Deal scheme provides long term finance to cover all or part of your costs. These costs are recovered through your electricity bills using the savings you have made by using the turbine. Because the payment value should not exceed your saving this should mean that the installation doesn’t cost you additional money over what you would usually spend on your electricity bill. The scheme does include 7% interest in the payments however, so you will make more of a saving overall if you can afford to pay for the installation upfront. To find out more about the Green Deal, visit our Green Deal page.
In terms of maintenance, your installer will be able to give you specific guidance on any maintenance checks that need to be carried out. Usually it is recommended that you get your system professionally checked yearly at a cost of £100-£200. The turbine system comes with a lifetime warranty but the inverter may need replacing during that time at a cost of £1,000-£2,000 for larger systems. Any batteries used with the system will usually have to be replaced every 6-10 years.Find an MCS accredited local installer
The Benefits of Domestic Wind Turbines
An average household installing a well-sited domestic wind turbine system could benefit by over £3,200 a year. This includes the money you could save on your electricity bill as well as the Generation Tariff and Export Tariff payments you could receive from the FIT scheme. Our Feed-In Tariff scheme page contains more information on this new initiative. Domestic wind turbines deliver additional benefits:
- Reduce your carbon footprint: A 6kW pole-mounted wind turbine system can save around 5.2 tonnes of CO2 a year.
- Pays for itself quickly: Larger systems have a payback time of around 7 years at current tariff rates, meaning that your system’s payback time could be similar or less.