Located at Caversham Weir, the twin-screw Archimedes turbine will generate 300 Megawatt hours of energy per year.
The River Thames at Reading passes over Caversham Weir with a drop of about 1.4 m and an average year-round flow of about 37 m³/second. Reading Hydro will be harnessing this potential energy by building a power plant comprising two SpaansBabcock-built Archimedes screw turbines, rated together at 46 kW of usable power output for a total of around 300 Megawatt hours per year.
The turbines are to be located in a structure, constructed by Land & Water, close to the northeast end of the main group of gated weirs, which cuts through a causeway linking the weirs to View Island and lower Caversham. This structure will comprise of the trough in which the screws will sit (at a 22 degree angle from horizontal), a turbine house containing the gearboxes, the generator equipment and electrical switches, as well as sluice gates and screens for the intake channels that lead from the Mill Stream into the Weir pool below.
For more detailed technical description of our hydroelectric power scheme, particularly around the turbines and the Fish Pass, check out the ‘Technical Overview’ page.
hang on, what is a ‘hydroelectric power scheme’?
Hydroelectricity is power generated from the movement of water. For example, you may be familiar with big dams of stored water, or in Reading Hydro’s case, naturally flowing rivers. The key thing is that when there is movement of water, there is potential energy that could be converted into electrical energy. All of this without burning fossil fuels – clean, green energy.
How is this achieved? Turbines harness a drop in water height, or ‘head’, and the speed of the river, or ‘flow’, to work. The head acts as the driving pressure, using the weight of the water to push the turbine. Flow (usually considered on average to account for seasonal variability) dictates turbine rotation speed. These two things are proportional to each other – the higher they both are, the more potential energy there is. Therefore when the water flows, its both the combined push and speed rotating the turbines.
To make something useful from this action, we connect the screws to electrical generators, and these covert the kinetic rotation into electricity we can export. In Reading, we’re using the sheer force and weight of the water falling across Caversham Weir to drive our turbines and generate this green electricity. See this link from Community Energy England for more educational details on this process.
There are already several hydro power schemes on the River Thames; the nearest ones are in Mapledurham and Sonning. There are also ones further afield in Osney, Sandford and Windsor – all of them use Archimedes Screw turbines.
In summary, we use the energy of the water at Caversham Weir and turn it into rotational kinetic energy using Archimedean screw turbines. These turbines turn our electric generators and they covert that energy into our hydro electricity.
The screw turbines are completely safe for fish, and fish will be carried downstream through the equipment unharmed. However, the fish cannot swim upstream through the turbines. To remedy this, we will be installing an additional natural fish pass on View Island. This will facilitate the upstream passage of fish, eels and lamprey. The fish pass will also provide some new spawning grounds for all fish along its route. There will be new habitats for flora and fauna too.
The government set up the Feed-in-Tariff (FiTs) scheme several years ago to encourage renewable generation. We obtained FiT successfully, meaning for each kWh of electricity that we generate, we will receive a small sum in payment. On top of this, we can sell any generated electricity to a private consumer or back to the National Grid. By doing so, we generate sufficient income to pay for the installation. This means that once it’s paid for, the whole installation becomes a community asset for the benefit of Reading. Even better, during the first twenty years of operation, we are forecasting a surplus we can direct to support local initiatives. That’s plenty of community benefit for many years to come.