Our hydroelectric plant, with two Archimedes screw turbines, is next to Caversham Weir in Reading
The River Thames at Reading passes over Caversham Weir with a drop of about 1.4 m. The water flow is about 37 m³ per second on average. This high-energy combination was harnessed to power various mills based on View Island for hundreds of years. However, by the middle of the twentieth century they had all been decommissioned and demolished. Reading Hydro CBS has revived Reading’s water power tradition, by building a community-owned hydroelectric plant that generates low-carbon renewable electricity.
Our power plant has two Archimedes screw turbines built by Spaans-Babcock, each connected to an electric generator via a gearbox. The whole plant is rated at 46 kW of electrical output, and we estimate it will generate an average of 320 Megawatt hours of electricity per year, without producing climate-heating emissions. Our site is located to the northeast end of the gated weirs, cutting through a causeway linking to lower Caversham. Each turbine sits in a concrete channel, constructed by Land & Water, at a 22 degree angle from horizontal. The intake channels are controlled by sluice gates and covered by screens to keep debris out. The water flows from the Mill Stream, through the screws and into the Weir pool below.
The turbine house is built from recycled aggregate blocks, wooden roof trusses and insulated steel roof sheeting. It houses the electrical generators, gearboxes, and electrical control and monitoring equipment. There are also integrated bat boxes for the local bat population in the North wall!
Hydroelectricity in brief
The weight of the falling water falling through the screws pushes on the blades and makes them rotate, turning the gearboxes and generators. The power produced depends on both the drop in water height down the turbines, or ‘head’, and the rate of water movement through the turbines, or ‘flow’.
See this link from Community Energy England for more educational details on this process.
Our hydroelectric plant is safe for fish, which are carried downstream through the screw turbines unharmed. However, fish cannot swim upstream through the turbines or the weir. There’s a ladder-like ‘fish pass’ just next to the weir, but this is too steep for many types of fish. To remedy this, we have built a new natural fish pass on View Island. This carries water down from the Mill Leat and through the island, and emerges next to the turbine channels. The water flows out faster than the flow from turbines, which attracts fish and eels into the pass. Eels are helped by a rough ‘eel tile’ on the floor. The fish pass also provides new resting and spawning grounds for fish along its route. We built other new habitats for flora and fauna too, with bird boxes, bug hotels and tree planting throughout View Island.
Reading Hydro raised £1.2m to build the hydro plant through a community share offer which attracted over 750 investors, mainly local people. We earn income by selling electricity, most to a private customer and the remainder to the national grid. We have also been successful in obtaining pre-accreditation for Feed-in-tariff (FiT) payments. The FiT scheme was set up by the government several years ago, to encourage renewable electricity generation by paying an agreed sum for each kWh of renewable electricity generated.
Once we are covering operating costs and setting aside a reserve for maintaining the system, we will pay a modest return to shareholders and gradually pay back their capital. After that, any surplus income will go into a community fund to support local low-carbon and other sustainability projects. Once all capital has been repaid to investors the whole hydro plant will become a community asset.
Read more in our March 2021 business plan. (Note that some details in this are now out-of-date, including names of directors.)