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Introduction to Low Head Hydropower
Most locations for large dam hydropower plants have now been exploited, or are too politically hot because of flooding large areas of land, displacing indigenous people’s homes and ruining livelihoods, submerging national historic buildings, along with environmental constraints.
Low head hydropower such as run of river hydropower plants has become more popular, but even these small plants can have a negative effect on the environment.
This is an article in civil engineering on low head hydropower, and here we will examine the new technology in this area that is being tested at Technische Universität München in Germany. (TUM)
We begin then with a look at an existing type of low head hydropower and then examine the new “shaft hydropower".
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Low Head Hydropower - an Overview
Before we examine the latest improvement to low head hydropower, it will be beneficial to identify and define the different sizes of hydropower designs by their output:
- Large Scale Hydro – output over 30MW
- Small Scale Hydro – output between 1 and 30 MW
- Low Head Hydro – output under 1MW
- Mini Hydro – output 1000kw and under
- Micro Hydro – output of 100kW and under
- Pico Hydro – output of 5kW
Typical low head bay type hydro plants are still pretty hard on the environment, both towards the fish population and the surrounding environment of the riverside ecosystem. The fish are provided with fish ladders, but can still be caught up in the system and killed by being held against filters or screens, smaller ones being swept through the turbine.
The ecosystem suffers through the disruption caused by the installation of the supply and discharge piping, as well as the building of a powerhouse.
A dam is required to supply the turbines with water, these being housed in a large, riverside powerhouse from where water is returned to the river via the turbine tailrace.
All these components are highly visible, and can detract from the aesthetic quality of the countryside. However the fact that the electricity produced emits no CO2 to the atmosphere, and can supply an off grid home with renewable energy somewhat offsets the aforementioned environmental problems.
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Shaft Hydropower Low Head Hydropower
The recently tested low head hydropower unit has significant advantages over the conventional low head plants:
- Limited environmental impact, mainly through construction of dam on river.
- Fish can freely pass the dam through the addition of an adjustable gate.
- No powerhouse or visible piping required.
- Almost no visible impact, all components are concealed in the shaft under the river; except for small sub-station built alongside the hydropower unit.
- Cost reductions of 30-50% are projected on conventional low head hydro plants.
- The hydropower plant can operate on a 1 to 2m head, being half the head required by conventional low head hydro plants
- The plants can be supplied as a complete unit, ready to install into the shaft, and are suitable for home hydropower supply.
- Shaft hydropower can offer thousands of opportunities to third world countries to produce renewable energy at a low cost with minimum environmental impact.
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Operation of the Shaft Low Head Hydropower Plant
1. Dam and Gate
The dam is a conventional concrete river dam, except a vertically adjustable gate is fitted to the wall about mid-length section. This controls the level of the river through overflow from below or above the gate allowing the safe passage of fish up or downstream of the plant.
2. Turbine Plant.
The plant is installed as a complete module into a vertical shaft, then a wire mesh debris screen is fitted across the top.
The completely submerged low head turbine can be either reaction such as a propeller, or an impact turbine such as a cross-flow type depending on the river flow velocity available.
The water passes through the screen through a bulb turbine that uses a propeller to drive the integral power generator. The bulb turbine can also incorporate adjustable guide vanes/wicker gates to give optimum water direction and flow to the propeller blades. The water now continues through a draft tube into the tailrace and re-enters the river behind the dam.
Note: I have used a vertical bulb turbine in the sketch, as this would be my first choice of water turbine. (Remember my sketch is what I interpret a unit will resemble.)
3. Power Output Cables
The power cables can be run up the dam wall and onto the riverbank where they are connected to the substation. From here the power cables are buried and run to the house/final location.
Below is a sketch of the low head hydropower unit using a vertical bulb turbine, please click on it to enlarge: