Renewable Energy – Solutions for application in the communal energy infrastructure

HYDROPOWER |
15
The Francis turbine is a universally applicable water turbine, in
which the impeller is radially impinged from the outside.
The Kaplan turbine is an axial-flow water turbine and is used in
run-of-river power plants.
Possible applications and benefits for municipalities:
Small hydroelectric power plants with a capacity of
up to approx. 25 megawatts support a wide range of
potential applications:
• Power supply to remote villages and regions
• Improving infrastructure in already developed areas
• Covering the base load in the electricity grid
• Securing the supply of electrical energy
• Stabilisation of the groundwater level
• Reduction of climate-damaging emissions
Functional principle and design
Small hydroelectric power plants are usually run-ofriver
(RoR) power plants. They use the hydraulic energy
of flowing water and continuously convert it into electricity.
Pumped storage plants are to be distinguished
from this. These store the water in a reservoir and
generate electrical energy when needed.
A run-of-river power plant works as follows:
Run-of-river or what are also known as ‘diversion’
power plants may also be contructed to channel or divert
water to the power plant via an additional watercourse
alongside the weir and main water body. The
goal is to achieve a greater gradient in order to achieve
more energy.
Another important component in the hydro electric
power plant are the rakes. The metal grilles possess
a dual function. Firstly, they protect the turbine from
damage caused by floating refuse – such as branches
and rubbish. Secondly, the small rake distances prevent
fish from entering into the power plant. The mechanical
barrier moves the fish away from their migratory path
with the main current. In order to ensure the continuity
of flowing waters, plant operators often build devices
known colloquially as “fish ladders” at the edge of the
watercourse.
Run-of-river power plants are particularly suitable for
watercourses with high flow velocities. They achieve
very high efficiencies of up to roughly 90 per cent.
The water may first be dammed up at a wier or dam
wall but is not always required. The water upstream of
the power plant (headwater) is higher than the water
downstream of the power plant (tailwater). The steeper
the gradient, the greater the amount of energy generated.
The headwater is fed into the power plant to the turbine.
This drives a generator that subsequently generates
electrical energy (electricity) from the mechanical
energy. After power generation, the tail water flows out
of the plant.