Since the corn mill at Nethermills was demolished in the 1950s at least 20,700 megawatt hours of useable energy have passed over the two weirs in the centre of Ayr at a rate of 320MWh per annum, enough to power approximately 80 homes.
In 2015, the Energy Agency commissioned a hydrological study of the site. Electronic level gauging took place over a six-month period, followed by a feasibility and design study by Mann Power Consulting Ltd. The results indicated that a hydro power scheme on the north bank could generate up to 85 kilowatts, producing 50-85kW for around half of the time, and approximately 320 megawatt hours in a typical year.
In 2020 the Energy Agency set up a subsidiary company, Energy Agency Renewables Ltd, to install, own and operate the scheme on the site, to be named the Nethermills Hydro Scheme.
Existing views of Nethermills Hydro siteHydro Power Technology
Following a feasibility study, the technology considered most suitable for the sensitive site and providing the best financial return is an 85kW Archimedean single screw turbine. Meters and sensors connected to the generating set will measure the generation and flows and allow full, real-time monitoring and analysis of the performance of the system. The robust technology has an expected lifespan of around 50 years.
The scheme has been designed to minimise disruption to the ecology and fish habitat, improving the access for fish and eels migrating up and down the river.
The proposed design of the turbine powerhouse and mechanism will sympathetically blend into the environment, reflecting the colours of the nearby green hedge and river bank and Ayrshire College’s Riverside Building. CAD visions of the Nethermills Hydro Scheme consented design
The power provided will be available for local use and export to the grid and will provide revenue by sale of the electricity.
Ayrshire College buildings are very close to the site and have sufficient electrical demand to use almost all of the generated electricity. This electricity will be used to supply their Aeronautical Centre, Dam Park, Riverside Buildings and Electric Vehicle Charging Points.
Selling to the college will allow a higher price for the electricity than exporting to the grid. The college will benefit from a lower electricity price compared to the normal commercial costs as well as receiving 100% green electricity.
A grid connection has been granted by Scottish Power Energy Networks (SPEN) for up to 100kW of export.
Feed in tariff
Official approval has been received from Ofgem for receiving the feed-in tariff. This guarantees a payment for every kWh generated and a minimum price for every unit exported to the grid. The tariffs will be linked to the Retail Price Index and paid for 20 years following commissioning.
The chosen contractors are all experienced providers of Archimedes screw systems. Mann Power Hydro Ltd has been appointed as Project Managers to oversee the design and construction of the hydro plant.
The engineering design of the project has been provided by TJ Booth Associates.
The appointed turbine manufacturer is Vandezande BVBA (Belgium).
The civil engineering contract to construct the power plant is being finalised. A screw of a similar order of size to that on order for Nethermills
Impacts of construction works - A Controlled Activities Regulations (CAR) Licence has been obtained from SEPA. It stipulates the environmental protection aspects of the installation works as well as ongoing abstraction limits and conditions. A detailed Construction Method Statement will be drawn up by the appointed civils contractor to fulfil all conditions of the planning consent and CAR licence to ensure minimum negative impacts on the ground and ecology of the site. It will be the job of the project managers, together with the Energy Agency, to ensure the published method statement is adhered to, or adapted as necessary as the project progresses.
Fish Counter - To encourage further enhancement of the river environment a fish counter will be installed in the upper fish ladder. This will be made possible by a power and web connection supplied from the turbine house. Marine Scotland is funding the fish counter installation and ongoing monitoring and maintenance, in partnership with the Ayrshire Rivers Trust. Marine Scotland Science has awarded a design, supply and installation contract to Fishtek Consulting.
Archaeology - A report commissioned from a local registered Archaeologist states that all ground-works will be undertaken under close archaeological supervision. If any significant archaeology is discovered, the project may be held up whilst it is investigated. This has been added to the Register of Risks, although as the weirs were refurbished in 2007, it is not considered likely.
CO2 Savings - The 320MWh expected to be generated annually would save an estimated 147 tonnes of CO2 per annum.
The scheme should continue to generate green energy for many decades after its capital cost has been repaid. Future surplus funds can be used for projects to reduce carbon and fuel poverty in South West Scotland
A hydro scheme providing 100% green electricity is in keeping with South Ayrshire Council’s long-term development plan to regenerate the riverside area in a sustainable way
The scheme will make a useful contribution to South Ayrshire Council’s Carbon Management Plan
The project will raise awareness and understanding of the use of renewable energy technology
The physical link between the scheme and Ayrshire College gives it a strong educational value. It will allow study of its mechanical and electrical systems and the links between rainfall, water levels, energy generation and local ecological issues
There is potential for added financial and educational value by use of energy storage, as electricity and heat, by the College
The site will be a local attraction displaying information to educate visitors
An example of Archimedes screws and powerhouse
Where are we now?
Partly due to pandemic-related restrictions on access to title document archives, agreement has still to be reached on the lease of the land on which the system will sit. Terms also require to be finalised with the Crown Estate for the very small area of land below the lower weir which is the high tide mark. These discussions are in progress.
The civil engineering construction contract to prepare the groundworks and build the powerhouse is being finalised.
A deposit having been paid, the final detailed design of the Archimedes screw turbine, generation and control hardware is currently in progress in Belgium.
Ayrshire College has been asked to consider a draft Wayleave and Power Purchase Agreement. They have asked to be put in touch with a college that has a similar relationship with a Mann Power generation plant in Totnes, Devon, to learn from their experience.
Due to Covid-19-related delays, an appeal has been lodged with Ofgem to extend the commissioning deadline by 12 months. This is necessary for the scheme to qualify for the feed-in-tariff. This requires a change of law which is expected, following a consultation period.
We are lobbying alongside the British Hydropower Association for a 12-month extension which would allow enough time to build the hydro power plant. The turbine is expected to arrive in August or September with the scheme becoming fully operational by end November 2021.