Environmental Engineering Reference
In-Depth Information
developing countries [2]. The optimal way of integrating this technology in power systems
has been covered in many topics and scientifi c papers published over the last century and
will not be dealt with further here. Reference [3] presents an up to date approach to hydro
scheduling.
2.3.2 Small Hydro
A small-scale hydro is commonly defi ned as being smaller than 5 MW. At even lower powers
(
100 kW), the so-called microhydro is subdivided into dammed and run of the river schemes
in which there is no storage; a further distinction is into high and low head. It is estimated
that the world potential of small/microhydro is around 500 GW of which roughly only one-
fi fth has been exploited to date. A particular attraction of small/microhydro is that the resource
is often located in remote rural upland areas unserved by a conventional electricity supply,
but where the size of communities and their energy requirements are consistent with the
available supply.
The fl ow in a given river will vary greatly throughout the year, generally having, in the
Northern hemisphere, high values during the winter months and low values during the
summer months. In more tropical climates the fl ow is likely to relate to monsoon conditions.
These seasonal constraints are important. For example, a correctly sized small scale hydro-
power scheme in the UK will not be expected to have suffi cient water to run continuously
throughout the summer months. For this reason most small hydro systems are grid
connected.
Figure 2.1 shows the mean daily fl ow for the river Barle in Somerset for 1980 from January
through to December. The following observations can be made:
<
•
For two months in the summer the fl ow dropped to very low values, less than 1 m
3
/s.
•
The river fl ooded (over 20 m
3
/s for this river) on several occasions.
•
The river level tends to rise fairly quickly but this level reduces gradually; i.e. there is a
sharp 'leading edge' followed by a slow decay. This is a general characteristic of rivers.
Mean Daily Flow on River Barle (Somerset) Jan - Dec for 1980
35
30
25
20
15
10
5
0
Figure 2.1
The mean daily fl ow on the River Barle at Dulverton Somerset in 1980. (Provided by
Robin Cotton for CREST MSc notes, Loughborough University, 1998)
