Environmental requirements
The head height and flow of water available determine the amount of power that can be generated. When planning a hydropower plant attention needs to be paid to the seasonal and yearly differences in water availability. In particular for run-of the river power plants, the flow of water needs to be above a certain minimum all year round to be able to produce electricity all year round.
Engineering & Infrastructure requirements
Micro- and pico- hydro power plants are best suited for isolated areas where there is no electricity grid Off the grid power plants require local load controlling to stabilise frequency and voltage of supply. They have the advantage that they are generally designed for single households or small villages and can be developed with local materials and labour. For small pico-hydro turbines the turbine/generator set can be bought as a module “off the shelf”, whereas from micro-power plants upwards the turbines are especially designed for the location.
Starting from mini-hydropower plants upwards in size, conventional engineering approaches are used. The size of the machinery is then such that road access is advisable Mini-hydro power plants are most often operated grid connected.
Small hydro power plants generally have no form of water storage.
Planning requirements
In order to proceed with a small hydropower scheme, it is necessary to obtain the right to utilize all the land concerned and it is important to find out how contractors will access the different areas of the hydropower scheme with the necessary equipment. It is therefore wise to approach the relevant land-owners at an early stage in order to identify any objections to the proposed project and to negotiate access to the land. Since water courses frequently define property boundaries, ownership of the banks and existing structures may be complex. Failure to settle these issues at an early stage may result in delays and in cost penalties later on in the project (The British Hydropower Association, 2005).
The world wide estimated amount of installed small hydro capacity was 85GW at the end of 2008: 65GW were estimated to be in developing countries of which 60GW in China (REN21, 2009). The overall technical potential for small hydro is estimated to be between 150 and 200GW (IEA 2008).
Small hydro already provides electricity to a large number of households in developing countries where other technologies would be more difficult to install. Over the last 30 years the technology has been used and installed extensively in China, but also in Nepal, Vietnam and several South American countries, among others; the market for Africa is expected to grow (ESHA, 2005). Hydropower plants represent 27% of all CDM projects requesting validation (UNEP Risoe). In absolute numbers this implies 1351 projects and an installed capacity of 44'995MW (UNEP Risoe). Currently 553 projects are registered.
Technology development
Small scale hydro is a mature technology. It can profit from technology development done for large scale hydropower turbines.
Specifically for small scale hydro, expected technical improvements include developments in lower head turbines, in-stream turbines and turbines which have a lower impact on fish populations (IEA, 2008). In addition, reduction in operation and maintenance (O&M) are expected.
Further in the future, the development of hybrid systems that combine hydro with wind or even with hydrogen production for energy storage could be expected (IEA, 2008); particularly in combination with hydrogen this development is still at R&D stage.
Figure 4: Installed capacity of small hydro plants (REN21, 2009)
Technology development
Small scale hydro is a mature technology. It can profit from technology development done for large scale hydropower turbines.
Specifically for small scale hydro, expected technical improvements include developments in lower head turbines, in-stream turbines and turbines which have a lower impact on fish populations (IEA, 2008). In addition, reduction in operation and maintenance (O&M) are expected.
Further in the future, the development of hybrid systems that combine hydro with wind or even with hydrogen production for energy storage could be expected (IEA, 2008); particularly in combination with hydrogen this development is still at R&D stage.
Substituting traditional fuels by a the switch to electricity can reduce air pollution, improve health and decrease social burdens, e.g. from collecting firewood. The electricity can be used to increase income generating activities, in particular it can improve irrigation, crop processing and food production (ESHA, 2005). The income generating activities may provide more jobs to the rural communities.
In a study for the UK Department for International Development (Fulford et al., 2000), the poverty reduction potential of small hydropower has been found to be significant, particularly in low-income countries. Micro-hydro has also been found to be a relatively efficient method of poverty reduction, in terms of costs per person moved across the poverty line. In addition, the estimates of poverty reduction from micro hydro are systematically understated, as they exclude a range of very difficult to measure, but important effects, including savings from no longer having to carry firewood, kerosene or other fuel, improved education through the availability of electric light and improved health and agricultural production from drinking and irrigation water which is made available by channels originally built for micro-hydro schemes.
Small scale hydro, being a renewable energy also has the advantage of reducing dependency from fossil fuels on the macro-economic level, if the country imports fossil fuels.
In a study for the UK Department for International Development (Fulford et al., 2000), the poverty reduction potential of small hydropower has been found to be significant, particularly in low-income countries. Micro-hydro has also been found to be a relatively efficient method of poverty reduction, in terms of costs per person moved across the poverty line. In addition, the estimates of poverty reduction from micro hydro are systematically understated, as they exclude a range of very difficult to measure, but important effects, including savings from no longer having to carry firewood, kerosene or other fuel, improved education through the availability of electric light and improved health and agricultural production from drinking and irrigation water which is made available by channels originally built for micro-hydro schemes.
Small scale hydro, being a renewable energy also has the advantage of reducing dependency from fossil fuels on the macro-economic level, if the country imports fossil fuels.
Depending on what forms of energy use the hydro powered system substitutes, the decrease in air pollution and GHG emissions differs, but given that small hydropower is virtually CO2 neutral, it is expected to be a significant improvement compared to conventional electricity production in terms of emissions of GHG and air pollutants.
In contrast to large hydro-power installations, the environmental impacts on the ecosystems are limited. Small hydro power plants require limited changes to the flow of the river and therefore the existing ecosystem can continue to function as before; improvements in this field in particular related to the development of “fish-friendlier” turbines, are nonetheless expected (IEA, 2008).
In contrast to large hydro-power installations, the environmental impacts on the ecosystems are limited. Small hydro power plants require limited changes to the flow of the river and therefore the existing ecosystem can continue to function as before; improvements in this field in particular related to the development of “fish-friendlier” turbines, are nonetheless expected (IEA, 2008).
A hydropower plant runs practically CO2 free. The main emission source is the production of the components and the transport to the location of the power plant.
According to the Energy Technology Perspectives 2008 the generating costs for small hydro power are between 0.02 and 0.06 USD/kWh (IEA, 2008). In older studies the capital costs, based on the average of case studies have been determined to be approx. USD 965 per installed kW (Khennas, 2000). Figure 5 shows some costs estimates for electricity generation and investment costs from European countries. 
Considering that some power plants have rather large upfront investment costs it is important to verify if the hydrology in the region will remain constant over time.
The capital requirements for small hydro plants depend on the effective head, flow rate, geological and geographical features, the equipment (turbines, generators, etc.) and the required civil engineering works. Making use of existing constructions such as weirs, dams, storage reservoirs or ponds can significantly reduce environmental impacts and costs. In general, sites with low heads and high flows need a greater capital outlay as they require larger civil engineering works and turbine machinery to handle the larger flow of water. If, however, the system can have a dual purpose, such as power generation as well as flood control, power generation and irrigation, or power generation and drinking water purposes, the payback period can be shortened.
In addition, special attention should be paid to the cost of using water (water charges and/or concession fees) as well as to the administrative procedure necessary to obtain the water and building licenses. Operation and maintenance costs may represent 1.5-5% of the project costs (ESHA, 2005).
Generally, on a cost per kilowatt basis, larger small hydropower projects tend to be cheaper due to economies of scale and the sunk costs of any scheme, irrespective of its size.
Figure 5: Investment costs for small scale hydro energy (Source: ESHA 2005)
The capital requirements for small hydro plants depend on the effective head, flow rate, geological and geographical features, the equipment (turbines, generators, etc.) and the required civil engineering works. Making use of existing constructions such as weirs, dams, storage reservoirs or ponds can significantly reduce environmental impacts and costs. In general, sites with low heads and high flows need a greater capital outlay as they require larger civil engineering works and turbine machinery to handle the larger flow of water. If, however, the system can have a dual purpose, such as power generation as well as flood control, power generation and irrigation, or power generation and drinking water purposes, the payback period can be shortened.
In addition, special attention should be paid to the cost of using water (water charges and/or concession fees) as well as to the administrative procedure necessary to obtain the water and building licenses. Operation and maintenance costs may represent 1.5-5% of the project costs (ESHA, 2005).
Generally, on a cost per kilowatt basis, larger small hydropower projects tend to be cheaper due to economies of scale and the sunk costs of any scheme, irrespective of its size.
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