6 SMALL HYDROPOWER SYSTEMS

6.1 Introduction

6.1.1 Background

The unending natural process resulting from the action of the sun's radiant energy on the earth's atmosphere, called the hydrologic cycle (figure 6.1), provides a continuous and renewable supply of water onto the earth's surface. A portion of this water returns to the sea during the cycle in the form of surface water runoff. Its potential energy is normally dissipated as the water flows downhill, but can be harnessed as a viable energy source to generate mechanical power or electricity.

 

Figure 6.1 The hydrologic cycle

 

This section deals specifically with Small Scale Hydropower systems, since large-scale hydropower plants are usually not considered as RES exploitation systems by ecologists and are covered on other INTUSER pages (LINK). Large dams have acquired a reputation for damage to ecosystems. They hood and silt in natural stream areas and deplete oxygen from the water. Their reservoirs are dead-water or slack-water pools whose water is hostile to native fish species. Downstream, they create alternating periods of no water followed by powerful surges that erode soil and vegetation.
Small Hydropower Plants (SHP) are mainly "run of river", i.e. not involving significant impounding of water and therefore not requiring the construction of large dams and reservoirs, though where these exist and can be utilised easily they do help. There is no general international consensus on the definition of SHP; the upper limit varies between 2.5 and 25 MW in different countries, but a value of 10MW is becoming generally accepted and has been accepted by ESHA (the European Small Hydro Association).

The definition for SHP as any hydro systems rated at 10MW or less will therefore be used here. SHP can be further subdivided into "mini hydro" (usually <500kW) and "micro hydro" (<100kW). Whichever size definition is used, SHP is one of the most environmentally benign forms of energy generation, based on the use of a non-polluting renewable resource, and requiring little interference with the surrounding environment.