Hydroelectric Power

Hydro-electric systems convert potential energy stored in water held at height to kinetic energy to turn a turbine, which in turn produces electricity.

Of course, hydro-electric power is only possible where there is a usable source of running water. Simply having a stream is not enough: you need to either have a sufficient drop in your watercourse to create sufficient water pressure to turn a turbine, or you need to be able to create such a drop by damming a stream.

Hydro-electricity can be one of the cheapest methods of providing renewable energy, but it is also very site specific: you cannot simply order a ‘one size fits all’ system and plug it in, it requires careful planning and adapting to create a system that will work for your location. You require a high flow watercourse with a head of water (i.e. the vertical drop) in order to produce reasonable amounts of energy.

There are lots of variations on hydro-electric systems. For low-cost micro-hydro, using a fast flowing stream or river is the simplest solution. Damming a stream or river to create a reservoir requires a fair amount of engineering and has significant environmental impact. Utilising an existing weir or waterfall can be a simpler solution if you have one. One thing that is important: you need fast flowing water: flat water won’t work. If there is no head to create pressure there is no power.

Hydro-electric systems rely on both head and water flow. A good site has a combination of these two. Systems are generally divided into two categories, low-head and high-head systems.

Low-head hydroelectric power

Low-head hydroelectric power systems have less head but a much greater flow. In a low-head system, a larger quantity of water is required to turn the turbines. The turbines themselves have to be physically larger in order to handle this volume of water. Most low-head systems require a head of between 60cm and 4 metres (2–13 foot). Anything less than 50cm usually makes a hydro system unfeasible, except possibly as a hobbyist project for generating 20–200 watts with a home built system.

The low-head system pictured above, the ULH Stream from Seabell International, is designed for small micro-power systems. The system pictured is working with a head of just 90cm and produces between 1.3 - 1.6kW of power.

A flow from a river or a stream will vary throughout the year, depending on the seasons. This means that the amount of energy you can take from your watercourse will be more susceptible to change in comparison to a high-head system where flow is less important than the drop (head) of water.

Examples of low-head waterways include locks on canals and weirs on rivers. The low-head is often man made, damming the river to create the pressure required. It is possible to utilise existing dams, such as weirs. Most waterways in lowland areas tend to only be suitable for low-head systems.

There are lots of examples of community projects getting together to develop their own hydroelectric power systems, often using an existing weir as a suitable dam to create a head of water. Utility companies too, harness low head run-of-the-river systems too in order to produce smaller hydroelectric power stations. In Germany, for example, there are a number of smaller hydroelectric power stations built along the rivers. The one pictured below is situated on the upper levels of the Rhine and produces 16MW of power. In total, all the small river-based hydroelectric power stations in Germany produce around 500MW of power, a total of 1.4TWh of energy each year.

Anatomy of a low-head hydro system

Anatomy of a low head hydroelectric power system

  1. There is a guard across the intake to stop debris, weeds and fish from entering the hydro-electric system. Some designs need further filters for removing smaller particles.
  2. The dam could either be constructed for this project, or an existing weir could be utilised. A dam can be as complicated as a fully engineered construction, or as simple as a pile of stacked up rocks and stones.
  3. The pipe transports the water to the turbine. Pressure is increased by the flow of the water pressing against the dam and pushing its way through the pipe.
  4. The generator is turned by the turbine, generating electrical power.
  5. The turbine is spun by the pressurised water forcing its way through. There are a number of different turbine designs, each with different characteristics that make them suitable for different types of watercourse. This diagram depicts a Kaplan Turbine which consists of an adjustable pitch blade propeller inside a tube. The pitch of the blades can adjust according to the flow of the watercourse.
  6. Draft tube. In this design, the vertical drop acts as a suction, pulling the water from behind it, thereby increasing the pressure further and forcing the water through the turbine faster.

High head hydroelectric power

High-head systems have a big drop but do not require a large flow of water: the pressure is created with gravity and the water hits the turbine as a high pressure jet. The size of the turbine itself can be more compact and the environmental impact of the system is considerably less. Much of the hardware can often be buried underground, thereby reducing the visual impact of the overall system.

High-head systems typically only work if you have a hill with a stream tumbling down the hillside. For this reason, they have become popular in hilly and mountainous areas, particularly with remote dwellings and farms, where a high-head hydro system can be more cost effective that connecting a property to the power grid. In order to install a residential hydro system, a high-head system typically requires a drop of at least 15 metres (46 feet), whilst many professional installers insist on a drop of at least 20 metres (62 feet) in order to create a workable system producing at least 5kW of power.

If your requirements are more modest, generating just a few hundred watts of power, then your system can be smaller. A number of people have successfully implemented 300w – 1kW sized high-head systems with 5–10 metre (15 –30 foot) drops.

Anatomy of a high-head hydro system

Anatomy of a high head hydroelectric power system

  1. The Intake captures part of the water from the stream. This can be as simple as a pipe submerged into a stream or as complex as a dam spanning a river. There is a guard across the intake to stop debris, weeds and fish from entering the hydroelectric power system.
  2. A filter removes smaller particles from the intake. This can either be self-cleaning screen or a secondary tank that temporarily reduces the pressure of the waterflow in order for sediment to settle. Sediment falls the bottom of the area and is pushed back into the waterway.
  3. The water flows towards the power house where the power generation takes place. In this example, the water flows downhill through a pressurised pipe (called a Penstock). The force of gravity increases the pressure of the water through the pipe. The greater the drop, the greater the pressure that is created within the pipe.
  4. The Power House contains the turbine and generator. The pressurised water spins the turbine, driving the generator and generating electricity. The design has to optimise the flow of water to maintain efficiency, both with the water entering the power house to spin the turbine and to ensure that the water can exit without restrictions.
  5. The Turbine is the heart of your system, converting the power of the water into a force to spin the generator and create electricity. There are many different types of turbine for different types of application. Some turbines work fully immersed in water (known as reaction turbines), whilst others work with only partial immersion (impulse turbines).
  6. The height difference between the water intake and the turbine is called the Head.
  7. The water is then returned to the waterway through the Draft Tube.

Calculating the amount of power you have in your watercourse

You will need to measure the flow and the head of your watercourse in order to identify how much power there is in the course. There are various ways of doing this, all of which are described in more detail in the book. Once you have got these measurements, you can use the hydroelectric power calculator on this website to work out how much potential power you have in your watercourse.

To use this calculator, click on the Hydroelectric Power Calculator option in the Renewable Resources section of this website.