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 a scheme on the site, to be named Nethermills Hydro Scheme.
Previous views of Nethermills Hydro site
Following the feasibility study, the technology considered most suitable for this sensitive site, and providing the best financial return, was a 90kW Archimedean single screw turbine. Meters and sensors connected to the generating set measure the generation and flows and allow full, real-time monitoring and analysis of the performance of the system. This robust technology has an expected lifespan of around 50-60 years.
The scheme was designed to minimise disruption to the ecology and fish habitat, improving the access for fish and eels migrating up and down the river.
The design of the turbine powerhouse and mechanism was to sympathetically blend into the environment, reflecting the colours of the nearby hedging and river bank.
CAD visions of the Nethermills Hydro Scheme consented design
The power generated is available for local use by Ayrshire College with any excess exported to the grid, providing funds for future projects from the sale of the electricity.
A grid connection was granted by Scottish Power Energy Networks (SPEN) for up to 100kW of export.
Official approval from Ofgem for receiving the feed-in tariff 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 were all experienced providers of Archimedes screw systems. Mann Power Hydro Ltd were appointed as Project Managers to oversee the design and construction of the hydro plant.
The engineering design of the project was provided by TJ Booth Associates.
The appointed turbine manufacturer was Vandezande BVBA (Belgium).
The civil engineering contract to construct the power plant was awarded to Bailey Construction Ltd.
Impacts of construction works - A Controlled Activities Regulations (CAR) licence was obtained from the Scottish Environment Protection Agency (SEPA). This stipulated the environmental protection aspects of the installation works as well as abstraction limits and conditions. A detailed Construction Method Statement was 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.
Fish Counter - To encourage further enhancement of the river environment a fish counter was installed in the upper fish ladder, made possible by a power and web connection supplied from the turbine house. Marine Scotland funded the fish counter installation and ongoing monitoring and maintenance, in partnership with the Ayrshire Rivers Trust. Marine Scotland Science awarded the design, supply and installation contract to Fishtek Consulting.
Archaeology - A report commissioned from a local registered Archaeologist stated that all ground-works will be undertaken under close archaeological supervision. If any significant archaeology were to be discovered, the project would be held up whilst investigated. This was added to the Register of Risks, although as the weirs were refurbished in 2007, it was not considered likely.
CO2 Savings - The 320MWh expected to be generated annually would save an estimated 147 tonnes of CO2 per annum.
The hydro scheme passed its grid connection testing in February 2022 and the video shows the turbine turning and generating electricity.
Work continued onsite throughout December, January and into February 2022. The civil construction contract was extended to allow remaining works to complete following high water events throughout the autumn and winter months.
After benefiting early in the project from an unusually dry summer, the contractors encountered significant difficulties caused by high water levels during autumn and winter 2021. This situation occurred because of a month’s delay in the delivery of the turbine equipment from Belgium due to the steel supply chain problems linked to COVID-19 related fluctuations in global demand.
The final installation phases were delayed as high levels of rainfall over this time led to river levels rising rapidly affecting the progress of works. It had been our intention, through careful project planning to avoid this period, but with the steel shortages we inevitably ran into this difficult weather season.
Ultimately this resulted in the construction completion date being extended initially to the end of January, then further into mid-February 2022.
The contractors worked tirelessly throughout to meet challenging demands with weekly progress meetings ensuring we remained on-track for the official ‘opening’ at the end of February and electricity generation by March 2022. The civil contractors worked their way through finishing touches and their sub-contracted roof specialists Skygarden installed the sedum roof over two days in late January.
Delayed until water levels receded, the smolt/eel/lamprey works were finished and Vandezande engineers completed their commissioning works on the screw and by-wash gate.
The electrical contractor TLS Renewable Consulting Ltd and their sub-contractors completed the installation of the control system. Testing of this began in February and a short test allowing water to flow through and turn the turbine for the first time took place successfully on 7th February. This was completed in readiness for the G99 grid-connection test with SPEN on 15th February.
We were pleased to achieve successful completion of the project well in advance of the final commissioning deadline of 18th March 2022.
Cameras are situated on the nearby Ayrshire College building so time lapse footage of the site’s development is available here
The scheme should continue to generate green energy for many decades after its capital cost has been repaid. Future surplus funds will be used for projects to reduce carbon and fuel poverty in South West Scotland.
The project is raising awareness and understanding of the use of renewable energy technology and the site is becoming a local attraction.
Our thanks to RedSnappa for producing this amazing film of the project:
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