Drives & Controls July / August 2022

48 n CLEAN ENERGY July/August 2022 www.drivesncontrols.com Hydroelectric scheme delivers spill-over benefits I n a pilot project in Scotland, overflow water from a reservoir whose main role is to maintain river levels is being harnessed to produce enough renewable electricity to power around 100 homes. A hydroelectric generation scheme comprising a reversible- pump turbine, generator and regenerative VSD (variable-speed drive) has been installed at Lower Glendevon reservoir, whose primary function is to provide statutory minimum flow into the River Devon. When the reservoir is at full capacity, water spills over via a spillway into the river. A 15" pipe is sized to deliver the minimum compensation flow of 242 litres per second, directly to the river, as stipulated by the Scottish Environment Protection Agency (SEPA). The pipe passes into a compensation measuring house where it connects to a reverse-pump turbine supplied by the Japanese manufacturer Torishima which, in turn, powers an 85kW ABB asynchronous generator. When the reservoir levels are high, a secondary 24”pipe provides additional power generation capability. A 90kW ABB regenerative VSD converts the generator’s output into electricity to feed into the grid. If the grid no longer needs electricity or a connection is lost, a brake chopper and resistance bank can be activated to divert the generated power and dissipate it as heat. Without them, a lost connection could cause the turbine and generator to accelerate to around twice their normal speed, sending surge waves back upstream and potentially damaging the pipeline. In its first three months of operation, the scheme generated more than 113,000kWh of electricity, which ScottishWater was able to return to the grid, putting it on course to save at least 93 tonnes of carbon dioxide emissions annually. ScottishWater is also benefitting from the remote operation and monitoring facilities that form part of the project. Previously, its staff faced 90-minute journeys to the remote site. Being able to control the valves and monitor real-time data around flow levels, temperatures and power generation remotely has been a big benefit for the company. Work on the project began in 2017 with a feasibility study which looked at many potential sites for hydro schemes.“The installation at Lower Glendevon was effectively a trial and has proven the concept, which gives us the confidence to look at other sites where we can introduce this technology,” explains Tom Coutts, senior project manager for Torishima Service Solutions Europe (TSSE). Currently, around 69% of ScottishWater’s carbon footprint is a result of its electricity demand and it has identified 25 sites where renewable energy schemes could help to offset its energy usage to help it achieve net- zero by 2040. “These schemes are, by their nature, weather-dependent so it can be difficult to accurately predict performance into the future,”Coutts adds.“We have been impressed with what we have seen so far though, which has given us confidence to start identifying other facilities where we can look at introducing renewable power generation.” Jim Dow, ABB’s regional sales manager for Scotland, sees the Lower Glendevon project as“a good example of how existing infrastructure – in this case, the reservoir’s compensation measuring house – can be utilised to contribute towards net-zero targets. While the scheme itself is relatively small, it proves the concept and highlights how ABB’s drive and motor technology can play an important role in the journey towards decarbonisation. “A regenerative drive is the ideal solution for capturing energy and feeding it back to the grid, allowing flexibility on the variation on flow,”Dow explains.“The drive requires simplified cabling which makes the installation quick. There are fewer components which improves the drive’s reliability and provides a smaller footprint, which helps optimise space.” The drive was supplied by EDC Scotland, located in Erskine, which also offered engineering and commissioning support during the installation. The control panel was built by the Kilmarnock-based electrical engineering firm, AirdWalker & Ralston. n Overflow water from a Scottish reservoir has been harnessed the generate electricity, helping Scottish Water to achieve its net-zero target. The scheme uses a regenerative drive to feed electricity from a reversible pump turbine-generator into the grid. The Scottish Water hydroelectric scheme extracts power from excess water that flows from from the Lower Glendevon reservoir when it is full