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Small Scale Hydro Power for Hydro Electric Power Article June 19, 2024 at 3:03 pm 2024-06-19T15:03:23-04:00
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Small Scale Hydro Power

Small Scale Hydro Power for the Home

hydro energy iconGenerally, small scale hydro power is an important energy source with multiple advantages over other forms of renewable energy if designed and installed correctly. The kinetic energy of moving water is readily available 24 hours a day, small scale hydro power systems can exploit this free energy providing a low cost and reliable source of “green electricity”.

Generally, all you need for a “small scale hydro power” system is a stream or a river with enough water running through it and at the right volume or pressure so that it can drive a water turbine connected to an electrical generator to supply power to your home. Just as with a solar energy or a wind energy renewable system, you can also design a small scale hydro system to be either grid connected, grid connected but with some form of battery backup or as an off-grid stand alone system.

But what do we mean by a “small scale hydro” system. A small scale hydro power systems is nothing more than a smaller scaled down versions of the much larger hydro generating stations we see which use large dams and reservoirs to supply power to millions of people. Depending upon the physical size, head height and electrical power generating capacity, small hydroelectric schemes can be categorised into small, mini and micro scale hydro schemes as follows:

  • Small Scale Hydro Power: is a scheme that generates electrical power of between 100kW (kilo-watts) and 1MW (mega-watts) feeding this generated power directly into the utility grid or as part of a large stand alone scheme powering more than one household.
  • Mini Scale Hydro Power: is a scheme that generates power between 5kW and 100 kW, feeding it directly into the utility grid or as part of a battery charging or AC powered stand alone system.
  • Micro Scale Hydro Power: is usually the classification given to a small home made run-of-river type scheme that use DC generator designs to produce electrical power between a few hundred watts up to 5kW as part of a battery charging stand alone system.
small scale hydro house
Small Scale Hydro

Small scale hydro power systems, as well as Mini Hydro Systems or Micro Hydro Systems, can be designed using either waterwheels or the impulse turbine design.

The generating potential of a particular site will depend upon the amount of flow of the water, the available head which in turn is dependent upon the site conditions and location and the rainfall characteristics of the site.

If there is sufficient head and flow, small hydro power plants can be driven directly from a river or stream, called a “run-of-river” system built into or at the side of a river or a stream without the need to dam, divert or change the flow of water in any way. Making them the cheapest solution for generating power.

In a run-of-river hydro scheme, the flow of the water is not altered, so its minimum flow rate needs to be the same or higher than that of the proposed turbine output power ensuring maximum efficiency. The result is that the costs involved for a run-of-river scheme are much lower and have less environmental impact than other small scale hydro plants. The disadvantage is that the water flow rate is variable throughout the year and the system is unable to store the waters energy.

The development of a small scale hydro power electrical schemes which uses a small dam or weir, water storage reservoir (impoundment) or requires a diversion of the rivers water flow through tunnels or canals, requires far more water usage in total as well as more complex civil and ground engineering works to match the site elevation not to mention the environmental impact that’s proportional to the size of the scheme.

However, a reservoir impoundment system or high head system has a much higher electrical generating potential than that of a much smaller run-of-river scheme due to the increased volume and velocity of the usable water, compensating for the larger capital investment, but costs can be kept down with simple design and practical, easily-constructed civil and mechanical works.

How Much Power can a Small Scale Hydro Design Extract

Waterwheels and water turbines are great for any small scale hydro power scheme as they extract the kinetic energy from the moving water and convert this energy into mechanical energy which drives an electrical generator producing a power output.

The maximum amount of electrical power that can be obtained from a river or stream of flowing water depends upon the amount of power within the flowing water at that particular point. As the water is moving a hydroelectric system converts this kinetic input power into electrical output power.

In order to determine the power potential of the water flowing in a river or stream, it is necessary to determine both the flow rate of the water passing a point in a given time and the vertical head height through which the water needs to fall. The theoretical power within the water can be calculated as follows:

Power (P) = Flow Rate (Q) x Head (H) x Gravity (g) x Water Density (ρ)

Where Q is in m3/s, H in metres and g is the gravitational constant, 9.81 m/s2 and ρ is the density of water, 1,000kg/m3 or 1,0kg/litre.

Then we can see that the maximum theoretical power that is available in the water is proportional to the product of “Head x Flow”, as the pull of gravity on the water and the water density is always a constant. Therefore, P = 1.0 x 9.81 x Q x H (kW).

But the water turbine is not perfect and some input power is lost within the turbine due to friction and other such inefficiencies. Most modern water turbines have an efficiency rating of between 80 and 95%, depending upon the type, reaction or impulse so the effective power of a small scale hydro power system can be given as:

Available Power from Hydro System

Hydro Power Equation

Where: η (eta) is the efficiency of the turbine or waterwheel.

Small Scale Hydro Power Example No1

A small stream drops 20 meters down the side of a mountain producing a water flow rate of 500 litres per minute past a fixed point. How much power could a small scale hydro power plant generate in kilo-watts, if the type of water turbine used has a maximum efficiency, (η) of 85%.

The data given: Head = 20m, Flow rate = 500 Lts/min, Efficiency = 0.85 and Gravity = 9.81 m/s2. But first we must convert the water flow rate of 500 litres per minute into m3/sec.

1,000 litres is equal to 1m3, so 500 litres is equal to 0.5m3. One minute is equal to 60 seconds, then a flow rate of 0.5m3 per minute is equal to 0.00833 m3 per second.

Power (P) = η × g × Q × H (kW)

P = 0.85 × 9.81m/s2 × 0.00833m3/s × 20m

∴ P = 1.4 kW

Now 1.4kW per second may not seem that much, but this is equivalent to over 1.84MW ( 1.4 × 60 × 60 × 24 × 365 ) of free hydro electricity annually. As power is proportional to the product of “Head x Flow”, increasing either of these two factors and/or the efficiency of the hydro system would result in an increase in the generated power. However, annual electric energy production depends on the available water supply being reasonably constant throughout the year.

Components of a Small Scale Hydro Power Scheme

A typical small scale hydro power scheme, needs a stream, an intake system to divert the water, a canal or channel called a penstock to carry the diverted water, a water turbine or water wheel to convert the waters kinetic energy into a rotational mechanical energy and an electrical generator to convert this rotational energy from the wheel into electricity.

Small Scale Hydro Power

Although the actual components will vary for each small scale hydro power scheme, the type of scheme chosen will determine the need to build a diversionary weir or a dam or a forebay, which will ultimately depending upon the available “static head” of water and a typical small scale hydro scheme is shown.

If you are uncertain about the geographical surroundings, purchasing a local survey map of the area will enable you to obtain an idea of the amount of head available from river to turbine by measuring the details of the contours on the map.

Low head schemes up to 20 metres, (65 feet) allow for a range of hydro energy options from a single plastic water pipe to a trough running downhill from a diversionary intake above shooting water directly onto a turbine (probably Pelton style), with the turbine turning a generator.

Then small scale hydro power systems consist of a channel, pipeline, or pressurised pipeline (penstock) that delivers the water. A turbine or waterwheel transforms the energy of flowing water into rotational energy and an alternator or generator to transform the rotational energy into electricity.

Small Scale Hydro Generators

As well as the civil works, one of the hardest parts of designing a small, mini or micro hydro system for electricity production is choosing the correct generator to partner the water turbine or waterwheel. Generally speaking, waterwheels rotate at slower speeds than water turbines, so if a high speed generator is chosen, then a gearbox or pulley system utilising a belt or change may be require.

There are many off-the-shelf electrical machines available, and all have there advantages and disadvantages but permanent magnet alternators are by far the most popular choice in successful small scale hydro power designs.

Small Hydro DC Generators – these range in size from a few hundred watts to well over 3,000 watts and can be used to charge battery banks to store the electricity generated by the system, similar to charging a car battery. The most common type of permanent magnet DC (PMDC) generator is the Dynamo. Dynamos are a good choice for newcomers to hydro power as they are large, heavy and generally have very good bearings on the pulley shaft.

Old style diesel truck or bus dynamos are a better choice for waterwheels as they are designed to generate the required voltage and current at slower speeds with the emphasis on efficiency rather than on maximum power. Also, most bus and truck dynamos can generate power up to 500 watts at 24 volts which is more than enough to charge batteries and power lights for a small scale low voltage hydro system.

If batteries are included in the small scale hydro power design, they should be located as close to the generator as possible, because it can be difficult to transmit low voltage power over long cable distances. Also, small scale hydro generators always produce power when turning even if the batteries are fully charged, then a dummy resistive load such as an electric fire element is required to absorb and dissipate this excess power. This dummy resistive load can dissipate a lot of energy so can potentially get very hot, therefore it should be positioned were it cannot be touched.

Car alternators are also another popular choice among many do-it-yourself people for low voltage turbine generators, however, they require high rpm speeds and are not always very efficient. Automotive alternators also require an external power supply to power the electromagnets that create the magnetic field.

Automotive alternators limit their own current using a built-in regulator circuit. This stops the alternator from overcharging the connected batteries. However, an automotive alternator should never be connected to the battery bank in reverse or run the alternator at high speeds without the battery connected as the output voltage will rise to high levels (much more than 12 volts) and destroy the internal rectifier.

Many DC systems also use rectifiers to convert the low-voltage direct current (DC) electricity produced by the system into 120 or 240 volts of mains alternating current (AC) electricity for household appliances and TV’s that run on AC electricity.

DC generators can supply power to a grid-connected system via an inverter and power conditioner but for a permanently grid connected system it is better to install an AC hydro generator.

AC Small Hydro Generators – are used for grid connected schemes and can be single-phase or three-phase machines. AC hydro generators have ratings of between 500 watts and 10kW using high speed synchronous or induction machines. AC hydro generators are connected permanently to the wiring system of the house, supplying the loads directly. The system should include a power conditioner to ensure that the output to the utility grid is always steady and at the correct voltage and frequency regardless of the speed of the turbine.

If you are lucky enough to live near to a river or stream, investing in a Small Scale Hydro Power System, can reduce your need for fossil fuels helping to reduce air pollution. There are many factors to consider when designing a hydro energy system, but with the right site and equipment, careful planning, and detailed attention to the local laws and permits required, small scale hydro power systems can provide you with a clean, reliable and maintenance free source of power for many years to come.

Besides the advantages associated with selling your own generated free electrical power back to your local utility company, grid-connected hydro electric systems will supply the additional power you need when your hydro power system cannot meet all your power requirements.

For more information about Small Scale Hydro Power and how to use motors as generators to generate your own electricity using the power of water, or obtain more hydro energy information about the various small scale hydro power systems available, or to explore the advantages and disadvantages of hydro energy, then Click Here to order your copy from Amazon today and learn how to use electrical motors as generators as part of your own hydro generating system.

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31 Comments already about “Small Scale Hydro Power

  • Hi,
    How do you know which size of turbine (kW) to install? I know the mean flow rate is 14 m3 s-1, low head of only 1.5 m but an Archimedean screw should work, right? I also have a flow duration curve but really unsure how to size the turbine to meet a demand of 90,000 kWh of electricity for a project…

    Any help massively appreciated,

    • Electrical energy is Power (watts) multiplied by Time (seconds). As you state that you need 90,000 kWh (or 90 MWh) of electrical energy, then if we assume power is in kilowatts (kW) and the time is in hours (h), your 90,000 kWh = power (kW) x time (h).

      Thus, if you require your electrical energy for 1 hour per day, you would need a turbine of 90,000 kW. If you require your electrical energy over one full day (24hrs), then you would need a 90,000/24 = 3,750 kW turbine, etc. Therefore, you can use your flow charts with a 4kW (nearest integer number for losses) turbine. that is, the turbine will produce 4kW of power per hour, per day.

  • hi, I wonder if you can help ?
    I have installed a 4 inch pipe which reduces to 2 inch and has a 30 meter head. I have 240 litres per Minuite exiting the 2 inch pipe .
    I am looking to put a Pelton driven generator to run 240v off it.
    I am trying to find out what size nozzle, Pelton wheel and generator would be best suited for this application ?
    any advice would be greatly appreciated.

    • With a static head of 30m (100 feet) and a flow rate of 240 litres per minute (64 GPM), that’s a fair amount of water to drive an impulse turbine. The dynamic head will be less than the physical static head because the flow of the water through the pipes involves liquid friction and turbulence that produces some losses, but you will still have a good flow rate. The attached alternator will also add friction and braking effect to the turbine, especially as the output current (and therfore power) increases.

      Nozzle orifice sizes are generally sized by manufacturers based on potential range of flow. Nozzle sizes of 1/2″ to 5/8″ in diameter for two nozzles, or smaller (1/4″ to 7/16″) for more nozzles. Note though that too many nozzles could cause too much water to be taken in and the penstock pipe to empty. Too big of a nozzle without enough water can cause air to be sucked into the penstock pipe. It’s trial and error for your particular installation.

      • thank you for that. I am about to fit a pressure gauge to give me an accurate static head reading,
        with it in mind to then drill a ten mm hole to start with to see what flow I have and to see the impact of the pressure reading . I anticipate something in he region of 55lites/min flow, but we shall see. I am then going to increase the hole size and record impact on my pressure and flow changes.
        obviously as the hole gets larger the pressure will reduce.
        what percentage drop would be optimal for best balance of flow and pressure for a Pelton please for producing 240v ?
        I know of a similar system running a 10mm nozzle running an 8 inch(12 spoon) Pelton wheel at 120 rpm producing 144v. it has 55 l/min of water exiting the system. he has lent me his spare generator for me to fit a Pelton and experiment.
        I fancy trying to get a bit more out of my system if possible.
        looking for some guidance as to best practise . do I order an 8 inch Pelton or different ? do I set up with 1 or 2 nozzles with my my flow ?
        I don’t know how to do the maths, will learn from trial and error but don’t want to just charge off blindly guessing . any thoughts or recommendations please?

  • I want to install Micro Scale Hydro Power at home and recycle the water from the roof to floor Which generator is suitable?

  • I am looking for someone to install a mini-hydro plant on my pond dam. Also where to purchase complete system. I am in South Carolina. Would like someone local..

  • Hello:
    My micro-hydro scheme locates at a small river. The flow of his river is 2 m3/s.And the head is 1.8 m. I would like to build a run of the water scheme without water storage. Is this feasible? Because of water species, I can’t utilize all the water in the river. My plan is using an intake make water going down to a small whirlpool turbine. My question is how many flow’s proportions should be used to generate electricity? 50% or 75? What is micro-hydro usually value?

    Best regards

    • Hello, is it possible to install a small scale hydroelectric turbines in a dam with the gross head of 6m, without river source and what wattage can possibly be generated?

  • Hello:
    My micro-hydro scheme locates at a small river. The flow of his river is 2 m3/s.And the head is 1.8 m. I would like to build a run of the water scheme without water storage. Is this feasible? Because of water species, I can’t utilise all the water in the river. My plan is using an intake make water going down to a small whirlpool turbine. My question is how many flow’s proportions should be used to generate electricity? 50% or 75? What is micro-hydro usually value?

    Best regards

  • I am uncertain how to design the micro hydro or mini hydro system I need.. First of all what are the advantages and disadvantages of generating ac current versus dc current? Would I use a generator or an alternator to do this? Dayton makes a 120 volt generator/turbine combo. Other companies make a 24 dc generator/turbine combo… Which is better? If I understand correctly I can store the electricity in batteries with a dc system and convert it to ac current with an inverter, but would it produce 240 volts or only 120 volts? Am I correct in assuming that I cant store ac current? So what are the advantages of making dc current and converting it to ac current with an inverter?

    Next thing is that I don’t really know if I want a stand alone system or if I want to be able to sell the power back to my local utility co. Can I do this with a dc system as well as an ac system? We are subject to frequent power outages here every time a tree branch falls on their power lines.. Earlier this month we were out of power for ten days due to heavy snow and trees falling all over the place…… How would utility company power outages affect my micro or mini hydro system? Would I have to install some kind of a switch so that I don’t send power back to the utility company when they are working on their transmission lines?

    Finally I have a 1350 gallon water holding tank about 40 or 50 feet above my house… The point of diversion for ths tank is a creek about another 40 or 50 feet higher up the hill than that.. It will be a concrete enclosure placed in the stream with a 2 inch hole at the top of the enclosure for a pipe and a concrete over it so the that water will not enter the enclosure from the top. It will enter the enclosure from the bottom and filter up through about 12 inches of small rocks to reduce the sediment in the system. My question is how do I figure the head and flow.. Is the head measured from the highest point of diversion in the creek way up on the hill or is it measured from the 1350 gallon holding tank half way up the hill? The tank will have a two inch intake pipe and a two inch pipe overflo pipe located at the top of the tank going down to the turbine… Is that big enough or is it too big? Should I use a smaller pipe?.. I cant use a larger pipe as the tank has 2 inch holes at the top and bottom. There is another inch and a half hole to supply water to the house.

    • This is a lot of questions in a single post and we will not attempt to answer them all, but to comment on the difference between AC and DC supplies. You are correct that batteries can only store DC energy and not AC, so if you intend to use battery storage then you will need a DC generator, or an alternator with rectification. The use of DC or AC depends on your proposed system, and whether you want an off-grid or grid connected system and power consumption. For long cable runs an AC supply is better than a low voltage DC supply, due to voltage drops, cable sizing, etc. and finally inverters take a DC supply and convert it (hence the name) to single-phase or three-phase AC, either 120VAC, 240VAC or 400VAC. There are many inverter types to choose from.

  • The worked example needs to be multiplied by 1000 to come up with the 1,390 watts answer.

  • How much it cost to generate 5kv electricity and does it produced round the clock and how long it sustained?

  • Really informative Article. Thanks for clearing my mind I am just recently entered in this field. Sir is there any ebook about the power generation of Electricity? If there is!! The let me know.

  • I can see how mini scale hydro electric generators would be connected directly to the grid. I have always been interested in cleaner forms of renewable energy. I definitely feel like we should look into using hydro electric power because it seems like an environmentally friendly alternative.

  • Dear sir,

    Please guide me to gain power from the discharge water/return water which is pump by 5hp pump 24 hrs

    At present we have fabricated a bulcart wheel having 22 pelton buckets and erected and rpm is around 75RPM and with increase in pully size we are getting finaly 600-650 RPM .

  • Hello.

    Good article.
    I think you have an error in power calculation:
    In the equation: Power (P) = Flow Rate (Q) x Head (H) x Gravity (g).
    You miss the density of water =997.0475 kg/m3 (at 25ºC)

    Correct equation: Power (P)[W] = Density Water (p) [kg/m3] x Flow Rate (Q)[m3/s] x Head (H)[m] x Gravity (g)[m/s2]

    Best Regards.
    Domingos Goncalves

    • The energy released by a body of falling water is defined as the vertical distance of the fall times the weight or the downward force exerted. The force is a product of the water’s mass (m) and gravitational acceleration (g). The energy released therefore is the vertical distance (h), or the head, multiplied by the force.

      Since power (P) is defined as energy per second, then the estimated power (W) = head (h) × flow (Q) × efficiency (n) × a multiplier constant

      This multiplier constant consists of water density x gravitational acceleration of the water. As water density is defined as 1,000 kg/m3 this is equivalent to 1.0 kg/L. If the flow rate is given in litres/min, then the constant can be written as 1kg/L x 9.81 m/s2 or just 9.81

      • My question is this our company dischages wastage water for 8 hour daily by 5hp motor pump .I want to use discharge pressure of water for rotating turbine .How much electricity can generated please help me . I am working on project

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