Technology

 

A Micro-Hydro Scheme using the energy produced by Weir to generate electrical power.

 

The Congleton Hydro technology relies on an Archimedes screw to convert the potential energy of the river flow to electricity. This type of equipment is extremely robust and we expect the lifetime of the scheme to be in excess of 40 years.

How does it work?

Energy from the weir is related to height and flow:

 

  • Water taken in via a pipe from above the weir flows through an Archimedes Screw and causes it to rotate. The screw is coupled to an electric generator and control system.
  • The output from the 75kW generator is transmitted at 400V to Siemens via a dedicated cable.
  • Having passed through the screw, the water is returned to the river.
    The screw is fish-friendly and there is zero water loss.
  • Sophisticated electronics enable maximum output over a wide range of river flow rates by controlling the speed of rotation of the screw.

The background to the site geology, development, civil works and construction techniques  can be found in the detailed article available to download.

Diagram of weir and hydro scheme  of

download – CIVIL WORKS & Construction

Connecting the Power to the Customer 

The Electricity generated by the scheme creates two sources of income. Electricity is exported to a local manufacturing site (owned and operated by Siemens plc) and sold to them at a commercial rate which is negotiated annually. Additionally, the government’s Feed-In-Tariff scheme currently pays a rate of 8.03p/kWh, which is adjusted annually in line with RPI and is guaranteed for 20 years.

After careful analysis and comparison, we found that it was most
economically efficient to install a private cable directly from the hydro to a suitably large customer, this being Siemens who have also been a very generous supporter of our project. A minor detail is that there is a distance of around 1km from hydro to user! To bridge this gap, we are using a long underground electric cable. Thanks to our  contractors, Duttons, for completing this part of the project!

 Our cable runs from the Power House to the Siemens factory via the grounds of Eaton Bank Academy and Eaton Bank Farm. A hidden gem? the cable is an essential, but hardly glamorous, component of the Congleton Hydro development. All the hydro’s electricity is exported through it and, hence, all its income flows through it. Maybe it is glamorous after all!

Download our detailed article describing this important step! 

Laying the electric cable to Siemens

Download – Power to the Customer

The Conundrum of the Inlet Pipe

When it came to specifying the design of the turbine inlet pipe nothing was quite as straight forward as it would seem.

Some background info. The amount of mechanical power that can be theoretically generated by the Archimedes screw (Pth) is, among other things, a function of the falling height of the water (the so-called driving head (H)) according to the formula.

Pth = Q x ρ x g x H
Where:
 
  • Pth = power theoretically available (W)
  • ρ     = density (kg/m3) (~ 1000 kg/m3 for water)
  • Q     = water flow (m3/s)
  • g     = acceleration of gravity (9.81 m/s2)
  • H = driving head (m of water) 

So, the smaller the value of H, the less power can be generated.

Practically speaking, H is a measurement of the difference in the height of the water in the forebay tank which feeds water into the turbine, compared with the river level at the turbine outlet.

We hope you find the following document of interest, it will help you appreciate the degree of design detail that goes into trying to achieve the optimum performance of the system.
 

Download – Conundrum of the Inlet Pipe

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