Fig Micro-hydro s economy of scale ( based on data in 1985)

Transcription

1 CHAPTER 1 INTRODUCTION 1.1 Purpose of the Manual for Micro-Hydro Development Micro-Hydroelectric Power, called as a Micro-Hydro, usually does not supply electricity to the national grid. They are used in remote areas where the grid dose not extends. Typically they provide power to small rural industry or rural communities. They range in size from a few kilowatts, just enough to provide domestic lighting to a group of houses, to 200kW, which can be used for small factories and to supply an independent local mini-grid which is not part of the national grid. There is an increasing need in many countries for power supplies to rural areas, partly to support industries, and partly to provide illumination at night. Government authorities are faced with the very high costs of extending electricity grids. Often Micro-Hydro provides an economic alternative to the grid. This is because independent Micro-Hydro Schemes save on the cost of grid transmission lines, and because grid extension schemes often have very expensive equipment and staff costs. In contract, Micro-Hydro Schemes can be designed and built by local staff and smaller organizations following less strict regulations and using the local technology such as for traditional irrigation works or locally made machinery. This kind of approach is known as the Localized Approach. Fig shows how significant a difference this can make the cost of the electricity produced. It is hoped that this Manual will help to promote the Localized Approach. Fig Micro-hydro s economy of scale ( based on data in 1985)

2 1.2 Components of Micro-Hydro Power Fig shows the major components of a typical scheme. Headtank Headrace Fig Major components of a micro-hydro scheme - Diversion Weir and Intake The diversion weir acts to divert water through an opening in the riverside (the Intake opening) into a Settling Basin. - Settling Basin The settling basin is used to remove sand particles from the water. The function of settling basin is very important to protect the following components from the impact of sand

3 - Headrace The headrace follows the contour of the hillside so as to preserve the elevation of the diverted water. - Headtank The function of headtank are to adjust the difference of discharge between a penstock and headrace, and to remove finally the litter in the water such as sand, driftwood

4 - Penstock Penstock is connected at a lower elevation to a waterwheel, known as a Turbine. - Turbine and Generator The turning shaft of the wheel can be used to rotate a mechanical device (such as a grain mill, oil expeller, wood lathe and so on), or to operate an electrical generator. The machinery or appliances, which are energized by the hydro scheme, are called the Load.In Fig the load is a saw mill. There are of course many variations on this design arrangement. As an example, the water is entered directly to the turbine from a channel without a penstock as shown at the saw mill in Fig This type is the simplest method to get the waterpower but recently dose not uses for electric power due to low-efficiency. Another possibility is that the channel could be eliminated, and a penstock run directly to the turbine from the first settling basin. Variations like this will depend on the characteristics of the particular site and the requirements of the user of scheme

5 1.3 Hydro Power from Water A hydro scheme requires both water flow and a drop in height (referred to as a Head ) to produce useful power. It is a power conversion system, absorbing power in the form of head and flow, and delivering power in the form of electricity or mechanical shaft power. No power conversion system can deliver as much useful power as it absorbs some power is lost by the system itself in the form of friction, heating, noise etc. Fig Head is the vertical height through which the water drop The conversion equation is : Power input = Power output + Loss or Power output = Power input Conversion Efficiency The equation above is usually expressed slightly differently. The power input, or total power absorbed by the hydro scheme, is the gross power, P gross. The power usefully delivered is the net power, P net. The overall efficiency of the scheme (Fig.1.3.2) is termed E o. P net = P gross E o kw The gross power is gross head (H gross ) multiplied by flow (Q) and also multiplied by a factor (g = 9.8), so the fundamental equation of hydro power is:

6 P net = g H gross Q E o kw (g=9.8) where head is in meters, and flow is in cubic meter per second. And E o is divided as follows. Eo = E civil work E penstock E turbine E generator E drive system E line E transformer Usually E civil work : (Channel length ~ 0.005)/ H gross E penstock : 0.90 ~ 0.95 (it s depends on length) E turbine : 0.70 ~ 0.85 (it s depends on the type of turbine) E generator : 0.80 ~ 0.95 (it s depends on the capacity of generator) E drive system : 0.97 E line : 0.90 ~ 0.98 (it s depends on the transmission length) E transformer : 0.98 E civil work and E penstock are computed as Head Loss (H loss ) usually. In this case, above equation is changed to following equation. P net = g (H gross -H loss ) Q (E o - E civil work - E penstock )kw This simple equation should be memorized: it is at the heart of all hydro power design work. It is important to use correct units. Fig Typical system efficiencies for a scheme running at full design flow

7 1.4 Where do Water Come from? The volume of river flow depends on the catchment area and the volume of rainfall. See Fig 1.4.1, the rainfall is divided to both sides (A and B) at the watershed. For instance, if a proposed Hydropower Plant is existing in A-side, the rainfall which is B-side, can not use for the power generation at the Hydropower Plant. Therefore the catchment area of proposed hydropower plant should be known at the first step of the hydro scheme. Fig The hydrological cycle The broken lines in Fig indicate the watershed of Pint-A and Pint-B. The catchment area is defined as the area which is enclosed with the broken lines. Fig The catchment area and the watershed