River turbines
Practical Action
The Design
The small-scale design designed by Practical
Action focuses on providing battery charging
facilities for remote communities. Typically, a
small turbine with a capacity of 200w could
charge 4 batteries in a day. The machine was
manufactured by the local company Tecnologia
Energética S.A.C. - Tepersac based in Lima, Peru.
turbine blades
The design of blades is achieved using concepts
used in wind turbine blade with the proviso that
in this case, the machine is subjected to much
stronger forces with, of course, a denser fluid
(water).
In order to calculate the diameter of the rotor,
following formula is applied:
P = ½ x ρ x (A) x v3 x Cp x h
A = (π x d2 / 4)
d = √ (8 x P/ π x p x V3 x Cp x h)
d : diameter of turbine rotor (m)
P : power of aero-generator design (Watts)
ρ : density of water (kg/m3)
V : velocity of river water (m/s)
A : area covered by the turbine (m2)
Cp : power coefficient (no dimensions)
h : efficiency of the generator
Figure 3: A robust and simple design was
developed for remote locations. A simple
permanent magnet generator was designed
(painted blue). Photo: Soluciones Prácticas.
λ = U/VD = π x N x d/60 x VD
N = (60 x λ x VD / π x d)
N : velocity of turbine rotor (r.p.m)
λ : tip speed ratio
U : tangential velocity at the tip of the blade (m/s)
Vp : design velocity (m/s)
The rotor
• Three fibre-glass blades
• Nominal diameter: 1.75m
• Turning speed: 45 rpm, at 1 m/s to the speed of river flow
• Two stainless steel supporting plates for the bucket mounting
The generator
In order to reduce costs, and to be able to rely on locally-made technology, Practical Action
began by working on the development of a permanent magnet generator. The magnets allowed
the speed of generation to be reduced, and lowered the cost of the equipment, which itself
could be adapted to be a river turbine rotor, and ultimately, tested and built. The main
components of the system are: the generation of alternating current which, via a system of
rectifying diodes, transforms the voltage to 12V, and 250W of power at 360 rpm.
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