River turbines
Practical Action
the velocity of the flow of water past the turbine. Therefore it is important to find the best flow
to get the best power output.
Hydro-kinetic turbines can
be classified into two types.
The first is the vertical-axis
turbine, whose turning axis is
perpendicular to stream flow;
secondly, the axial turbine,
whose rotational axis follows
the direction of flow.
Vertical-axis turbines are
preferable in situations
where flow direction
changes, such as in tidal
systems. These turbines are
designed so that the
direction of rotation remains
the same regardless of the
direction of flow.
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15
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0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 2.75 3 3.25 3.5 3.75
Velocity (metres)
Figure 2: Graph showing the relationship between the speed of
the river and the power available. The green line shows the power
in the river. The red line shows the power extracted by the
turbine.
Putting the theory into practice
For small scale low cost river turbines Practical Action found the second configuration to work
due to the simplicity of the design and its greater robustness. It also has the advantage of
building on existing knowledge from the small scale wind turbine projects previously
undertaken.
The experience from Peru highlighted the importance of siting the turbine. The minimum
workable velocity of the river is about 0.8m/s to 1m/s but preferably 1.3 to 1.5 m/s going up
to a maximum of 3 m/s for the type of floating turbines Practical Action has been involved in.
The engineering would need to be more substantial for higher river speeds.
Larger rivers are better in providing the right conditions for a turbine but flow of a river can
vary considerably over the year. In a full river the turbine can be located near to the bank and
still work in deep water but during the dry season the water levels can drop and the turbine
could potentially hit the bottom.
If the bank has a shallow incline then the edge of the water moves away from its originally
position as the water level drops and the turbine needs to be moved further into the middle of
the river.
Therefore it is important to find a site that has a site where the water will have a fast flow near
to steep banking.
A major hazard for river turbines in large rivers is debris such as logs or trees that have fallen
into the river. These can seriously damage the turbine and incur large costs.
Banks can be eroded away or become unstable and in extreme cases the river can change its
course. These environmental issues can be more challenging than the technical issues.
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