Microhydro

Despite often having access to wind or hydropower, about two billion people or one third of the earth's population have no electricity. Many small communities, especially in the developing world, do not have the resources to embark on a small hydro project, but micro-hydro is another matter. It covers systems providing between 10 and 100 kW of power. A typical case is the Vavanga Community, a village on the south west coast of Kolombangara Island, one of the Solomon Islands. It now has electricity thanks to Appropriate Technology for Community and Environment (APACE) based in NSW Australia, a non-profit community-based agency assisting overseas communities to engage in sustainable development.

The system consists of a timber weir feeding a four-pipe penstock which powers a turbine serving a 240 V AC synchronous generator with an output of 4-7 kW, depending on the season. The power is fed to the village 2 km away by a combination of underground and overhead cable. In the first instance 22 houses, 14 kitchens, two church premises and a bakery were connected to the supply. Typically two 18 W fluorescent lights and one power point are served in each household. To ensure that the river can supply an equitable amount of power when rates of flow vary, a current-limiting device is installed in each household. However, community facilities and businesses receive unlimited power.

Villagers took an active part in the installation of the project. As a run-of-river scheme it is mechanically relatively straightforward, which has enabled the villagers to be trained to carry out routine maintenance (see Fig. 10.2). Oversight is provided by APACE, which liaises with the community hydro committee regarding local resource utilization, local distribution and the design of buildings.

Figure 10.2 Villagers maintaining the plant (courtesy of Caddet)

The electrification of Vavanga and similar villages has a variety of positive impacts, not least the fact that it has slowed the population migration from villages to towns. There is now better village welfare. New homes are being built that are connected to the supply. There is a new church. Existing homes are being repaired and well maintained. There is street lighting.

The community plans to upgrade the system, first by replacing the timber weir with a concrete structure; and then by tapping an additional tributary of the river with a second penstock feeding a small turbine.

The cause of micro-hydro has recently been further advanced by the development of a 'power controller' by a Danish engineer, Steen Carlsen. This makes it possible to create stand-alone power plants much more cheaply. It supplies AC current to a quality matching that from a large public grid and at a price that is a mere fraction of that from traditional synchronous generators previously necessary for stand-alone plants. The device provides a fixed voltage within a margin of 1%. This has an impact on the life of light bulbs for example. If a filament bulb receives an excess voltage of 10% its life expectancy is reduced by 70%. In developing countries this is an important consideration. Another problem with isolated off-grid communities is that they have a problem with surplus electricity.

A village in the Peruvian Andes was the first to receive the power controller. The device maintains a steady three-phase output from a turbine-driven asynchronous motor by diverting surplus power to a heating cartridge (a large immersion heater) in a central tank which can distribute hot water to the community (see Fig. 10.3).

A further trick of the power controller is that it can 'deceive' conventional electric motors into acting as though they were connected to the grid. This allows cheap standard electric motors to be used as generators, enabling wind or hydro schemes to operate in either stand-alone or grid-connected mode.

The fact that the inhabitants can now heat their homes and domestic water from the micro-hydro source has meant that they are no longer reliant on wood from the surrounding

Figure 10.3 Typical village system with power controller

Electric motor as generator

Standard pump converted to turbine

Water returns to stream

Figure 10.4 Improvised micro-hydro with converted electric motor as generator

Penstock pipe minimum 500 m length and 50 m head

Electric motor as generator

Standard pump converted to turbine

Water returns to stream

Figure 10.4 Improvised micro-hydro with converted electric motor as generator forests. So, it is countering 'survival' deforestation and the erosion of soil which accompanies it. It is also providing power for small-scale industries and workshops, further placing a brake on the drift to the cities.

Finally, a Yorkshire farmer, Bill Cowperthwaite, has demonstrated how micro-hydro can come within the DIY range. His ideas have been adopted by the charity Intermediate Technology. The principle is to use components which are cheap and readily available in developing countries. What is required is a length of metal or PVC pipe for the penstock, a standard pump, and an electric motor. The pump is converted into a turbine by reversing the connections. If pumps are not available Intermediate Technology has devised a programme for teaching villagers how to fabricate turbines from waste metal. The electric motor can be converted into a generator. Electric motors work by generating an electric field within the motor which causes a magnet at the core of the motor to spin. Generators work in reverse by spinning the central magnet, causing current to flow to the external electromagnet. Capacitors are all that are required to convert the motors into generators. These store electricity for the short time required to even out the variations in voltage as the core rotates. It is reckoned that the cost of an electric motor and converting it to work as a generator is significantly less than the cost of a purpose-built generator for rating up to 20 kW. There is a bonus in that electric motors generally have heavier bearings than commercial generators, giving them a life expectancy of at least 10 years (see Fig. 10.4).

The final piece of the kit is an electric controller which manages the flow of electricity. As in the Peruvian scheme the controller directs electricity which is temporarily surplus to demand to a heat sink. The controllers can be made locally and are already being manufactured in numerous rural sites, for example in Nepal.

Whilst small hydro has considerable potential in the industrialized countries, micro-hydro in association with other compact renewable technologies raises the possibility of transforming the lives of rural communities in developing countries.

Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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