SRSP, Pakistan won an Ashden Award in 2015

In remote areas, small-scale hydro schemes can bring electricity for the first time to whole communities. This provides lighting, TV and communications for homes, schools, clinics and community buildings. The electrical power generated can be enough to run machinery and refrigerators, thus supporting small businesses as well as homes.

How small scale hydro power works

The power available in a river or stream depends on the rate at which the water is flowing, and the height which it falls down, known as the head. Hydro schemes are usually classified into four groups:

  • Large scale: 2MW and above
  • Mini: 100kW to 2MW
  • Micro: 5kW to 100kW
  • Pico: less than 5kW

The core of a hydro power scheme is the turbine, which is rotated by the moving water. Different types are used, depending on the head and flow at the site (see below). The turbine rotates a shaft which then drives an electrical generator.

How small scale hydro systems are used

Many micro-hydro schemes are remote from the mains grid, and a local grid is constructed to distribute the electrical power.

The output from the generator must match the demand for electric power on the local grid, otherwise the voltage and frequency can vary suddenly which can damage some electrical equipment. The demand for power in an off-grid system is often very variable, because people switch lights and machines on and off, so the supply from the micro-hydro system must be varied to keep close control. This can be done by varying the water flow, or by using an electronic load controller.

Hydro power schemes can be connected to a mains grid if one is available. The not-for-profit IBEKA was set up to provide community-managed micro-hydro schemes for off-grid communities in Indonesia. If the mains grid is extended to the region, IBEKA helps the community to get the micro-hydro connected to the grid, so that they can earn income from electricity sales. It also helps communities to set up grid-connected micro- and mini-hydro schemes from scratch.


A micro hydro scheme in Pakistan

In some micro-hydro schemes, the rotating shaft directly drives machinery. The Centre for Rural Technology, Nepal upgrades water mills so that they can grind more flour and in some cases run oil expellers and other machines as well.

Benefits

In remote areas, small-scale hydro schemes can bring electricity for the first time to whole communities. This provides lighting, TV and communications for homes, schools, clinics and community buildings. The electrical power generated can be enough to run machinery and refrigerators, thus supporting small businesses as well as homes. 

A prime aim of the micro-hydro schemes developed by GIZ-Integration in Afghanistan was to provide enough electricity for workshops and other small businesses, thus offering alternatives to opium production for earning income. Practical Action Peru also found that young people were more likely to stay in villages with micro-hydro, and that business activities grew.

The main environmental benefit of micro-hydro is reducing greenhouse gas emissions and local pollution from fossil fuels. This includes kerosene for lighting, diesel for running machinery, and fossil fuels for generating electricity.

Cost

The cost of small-scale hydro varies significantly with location. For example, SRSP’s hydro projects in Pakistan cost around $1,300 per kW in 2015, while GIZ-Integration’s schemes in Afghanistan cost between US$3,700 and US$5,300 per kW in 2012.

The future

There is substantial potential for supplying off-grid communities with electricity from small hydro schemes. The technology can be made compatible with the national grid so that an off-grid hydro scheme could subsequently be connected to the grid: all the GIZ-Integation schemes in Afghanistan have been designed in this way.

There are concerns about the environmental impact of large-scale hydro schemes because they require substantial areas to be flooded to provide reservoirs, and can have a serious impact on water management. Carefully designed small-scale hydro schemes take only a limited amount of water from a river or stream, have a small storage volume, and return the water a short distance downstream, and thus have very little environmental impact. Several small hydro systems have less environmental impact than a single large hydro scheme supplying the same power.

TGV won for their micro hydro installations in Wales

Types of turbine

There are several types of hydro turbine, each of which is suited to different flow rates and heads:

  • Pelton turbine: (for high head, low flow), which consists of a set of small buckets arranged around a wheel onto which one or more jets of water are arranged to impact. A variant is the Turgo turbine, which spins faster than a Pelton, making it easier to connect to a generator.
  • Francis turbine: (medium head and high flow), which has a spiral casing that directs the water flow through vanes on a rotor. It is commonly used in larger hydro schemes.
  • Cross flow: or Banki turbines (low head and high flow), which are made as a series of curved blades fixed between the perimeters of two disks to make a cylinder. The water flows in at one side of the cylinder and out of the other, driving the blades around. They are much easier to make than most other designs.
  • Propeller trubine: (very low head and high flow) has fixed blades, like a boat propeller. A more complex version, the Kaplan turbine, has blades that can be adjusted in pitch relative to the flow.