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Micro-hydro Technology History & Development

Originally, hydroelectric power stations were of a small size and were set up at waterfalls in the vicinity of towns because it was not possible, at that time, to transmit electrical energy over great distances. Whilst a hydroelectric power scheme uses a renewable source of energy that does not pollute the environment, the construction of dams to enable large hydroelectric generation may cause significant environmental damage, depending on local conditions. Micro-hydro installations can be designed to minimise the damage that may eventuate and, due to their relatively small size, they are less likely to cause major problems to the surrounding natural systems.


Types of Water Turbines Used in Microhydro Schemes

Water for a hydroelectric power station’s turbines can come from a specially constructed dam, set high up in a mountain range, or simply from a river close to ground level. As water sources vary, water turbines have been designed to suit the different locations. The design used is determined largely by the head and quantity of water available at the particular site.

The three main types are: Pelton wheels, Francis turbines, and Kaplan or propeller type turbines (named after their inventors). All can be mounted vertically or horizontally. The Kaplan or propeller type turbines can be mounted at almost any angle, but this is usually vertical or horizontal. There are two main types of turbines used in microhydro systems, depending on the flow and the head: impulse turbines and reaction turbines. Typical impulse turbines are the Pelton wheel and Turgo wheel, which are generally used for medium to high-head applications. Reaction turbines (of the propeller type such as the Kaplan turbine) are generally used at low or medium head (Fraenkel et al, 1991).

Hydroelectric Installations in Australia

The current total main transmission grid connected generation (GWh) in the period 2003 – 04 was 212,952.83 GWh. Just over 7.2 percent of this was derived from hydro at a total of 15,399.80 GWh (ESAA, 2005). For a table of the hydro installations in Australia click here.

The vast majority of Australia’s hydro capacity is derived from the installations owned by Snowy Hydro and Hydro Tasmania, approximately 50% and 30% respectively. The largest hydro projects were predominantly the first to be commissioned and produce the most amount of the hydroelectricity.


Small Scale Hydro Power

Hydro power is available in a range of sizes from a few watts to many gigawatts. A widely used classification scheme breaks hydro into a range of sizes, from a few hundred watts to over hundreds of megawatts. At the low end of the scale, small hydro can be divided into three categories: micro (less than 100 kW), mini (100 kW to <1 MW) and small (1 MW to <10 MW) (Parliament of Australia, 2001). This section focuses on microhydro systems, which are generally stand-alone systems, i.e. they are not connected to the electricity grid.

Micro-hydro systems operate by diverting part of the river flow through a penstock (or pipe) and a turbine, which drives a generator to produce electricity and the water flows back into the river (see Figure 1). Micro-hydro systems are mostly "run of the river" systems, which allow the river flow to continue. This is preferable from an environmental point of view, as seasonal river flow patterns downstream are not affected and there is no flooding of valleys upstream of the system (Harvey, 1993). A further implication is that the power output of the system is not determined by controlling the flow of the river, but instead the turbine operates when there is water flow, at an output that is governed by the flow. This means that a complex mechanical governor system is not required, which reduces costs and maintenance requirements. The systems can be built locally at low cost, and the simplicity gives rise to better long-term reliability. However, the disadvantage is that water is not carried over from rainy to dry season. In addition, the excess power generated is wasted unless an electrical storage system is installed, or a suitable ‘off-peak’ use is found.


Figure 1 A low-head micro-hydro installation
(Image adapted from Stockholm Environment Institute (Fraenkel et al, 1991)).

Micro-hydro systems are particularly suitable as remote area power supplies (RAPS) for rural and isolated communities, as an economically viable alternative to extending the electricity grid. The systems provide a source of cheap, independent and continuous power, without degrading the environment. It is estimated that in 1990 there was an installed capacity worldwide of small hydro power (less than 10 MW) of 19.5 GW (World Energy Council, 1994).

Electrical energy can be obtained from a micro-hydro system either instantaneously or through a storage system. In an instantaneous power demand system, the system provides 240 Volts of AC power to the load via a turbine that must be sufficiently large to meet the peak power demand. These systems require a large head and/or flow. In a storage system, the micro-hydro generator provides a constant DC charge to a battery system, which then supplies power to the load via an inverter. The battery system must be sized to the daily electrical demand. However, the turbine is significantly smaller than for an instantaneous demand system, and it operates at a constant power output.

Micro-Hydro Power in Australia

The use of micro-hydro systems in Australia is not well documented. A number of micro-hydro units are available (Tamar Designs, 1998) for domestic remote area power supplies, tourist facilities, cathodic protection for pipelines, etc. Currently, the typical cost of a 5 kW micro-hydro unit (excluding civil works) is around A$10,000 (Your Home, 2008). An example of a typical micro-hydro system in Australia is a home system situated on the Jack River, high in the Eastern Strzelecki Ranges, near Yarram in Gippsland, Victoria. The owner Leon Trembath receives year round power from 2 micro-hydro turbines. The capture pond is 2 by 1 metres, and flows through a 250mm diameter pipe to the turbines. The micro-hydro generators are 4 nozzle Platypus Power units with Turgo turbines. They generate around 450 watts each of DC electricity, which is fed into a 24 volt, 850 amp hour battery bank. According to Leon Trembath, the system has run flawlessly since 1994. With a little maintenance and a capital cost of less than $18,000 it compares favourably with the $20,000 grid connection fee and ongoing utility bills (Department of the Environment, Water, Heritage and the Arts, 2008). However, suitable micro-hydro resources, in locations where they can be utilised, are limited in Australia (DPIE, 1997).


Micro-Hydro Power in Asia

Micro-hydro installations are widespread in Asia, where there is a significant resource potential for further development. China has a well developed small hydro power industry with an installed capacity of over 19 GW, and the annual electric output to 64 TWh (International Small Hydro Atlas, 1998a). Hydropower supplies electricity to 300 million people in about 800 counties, covering nearly half of the country's area, and 70% of the mountainous area. The topography of Nepal is ideal for micro-hydro power, with high hills, scattered settlements and more than 6,000 rivers crossing the country. The installed capacity of micro-hydro power in Nepal is estimated to be 8.7 MW, with the economically viable microhydro potential at about 42 MW. The cost of stand-alone power plants is in the range of US$1,200-1,600 per kW (in 1993 dollars) (Rahmatullah, 1996). Such turbines are being used to grind grain, hull rice, and expel oil from oilseeds, as well as to generate electricity. It is estimated that more than 90% of Nepal’s microhydro installations are used exclusively for agroprocessing works. Estimates in 1998 indicate that almost 1000 microhydro plants were in operation (International Small Hydro Atlas, 1998b).

Vietnam has around 500 installations of micro-hydro systems in the 100 kW to 1 MW range, representing 10 MW of a potential 200 MW (or 5 per cent). There are also estimated to be 3000 possible sites for micro-hydro plants (rated up to 100 kW). Approximately 400 small hydro stations (1 to 10 MW) have been constructed, with a total capacity of 70 MW, representing only about 3 per cent of the potential in the country. However, more than a third of these plants (supplying around 20 MW) currently require renovation (International Small Hydro Atlas, 1998c). These sites will serve irrigation and drainage needs, in addition to generating electricity for 2 million households. Many areas in Vietnam do not have access to the electricity grid, due to the high costs of grid extension. In areas such as these, micro-hydro units are used by families for mechanical devices, lighting, battery charging and to power televisions and radios. It is estimated that over 3,000 family units of 1 kW or less are installed in Vietnam (Rahmatullah, 1996).

Other Asian countries with micro-hydro resources include Laos, with nine small, mini- or micro-hydro plants in operation (1998), with a total capacity of 10 MW. An 80 kW plant is under construction, and two more are planned, with a total capacity of 2.7 MW. A number of small hydro projects are also under construction jointly by Thailand and Laos (International Small Hydro Atlas, 1998d). Papua New Guinea has 10 small, mini- and micro-hydro plants (of less than 2 MW) in operation, with a total capacity of 19.8 MW (International Small Hydro Atlas, 1998e). In 1998, the Indonesian government announced its intention to electrify 18,600 villages using small and micro-hydro schemes, which is proving to be a challenging task (IJHD, 1999b). China’s rural electrification programme aims to continue to install 1 GW per year of small hydro capacity (IJHD, 1998b), with 318 counties having recently implemented rural electrification projects based on small hydropower. More than 97% of China’s rural households were supplied with electricity by 1998 and a rural population of 93 million have bid farewell to the days without electricity in those areas (International Small Hydro Atlas, 1998a). For an example of a typical micro-hydro installation see Figure 2).



Figure 2 A micro-hydro power unit installation in Bamerchara in Bangladesh (photo courtesy of the Renewable Energy Information Network).

The Future for Micro-Hydro Power Technology

As a cheap, renewable source of energy with negligible environmental impacts, micro-hydro power technologies have an important role to play in future energy supply, particularly in developing countries. It is an attractive alternative to diesel technologies in rural and remote areas of developing countries as a means of achieving rural electrification.