Case Study: West Harris Trust 100 kW hydropower scheme completed

Renewables first was hired in Spring 2015 by River Generation Limited (a subsidiary of West Harris Trust) to initially undertake a review of an existing feasibility assessment and preliminary construction designs for a hydropower scheme on Harris, in the Outer Hebrides, Scotland. Renewables First was subsequently hired to complete the designs, as well as project manage construction installation and commissioning.

The hydropower scheme draws water from the Abhainn watercourse where it drops 80 m throughout the rocky moorland terrain of Gleann Dubhlinn. The scheme has a 400mm diameter by 950 m long penstock connecting the intake structure to the 100 kW twin Jet Pelton turbine which is housed in a newly constructed turbine house. The water intake structure is a pre-existing Scottish water weir modified using a specially designed steel framework to accommodate a 3 m wide, 2 mm mesh Canada screen to filter waterborne debris from the water prior to entering the penstock.

Installation of the scheme was relatively straightforward. The image (above left) shows an overview of the Gleann Dubhlinn site, with the coast, moorland and mountainous terrain as the backdrop. The image (above right) shows the Abhainn Gil an Taillier on which the hydro scheme is located. There was only a footpath to the intake so before any construction works could begin, a track had to be created to enable vehicular access, including excavation equipment to dig a trench for the long penstock run.

The images above show the penstock pipe, connecting the water intake structure to the turbine house downstream, before being backfilled. The penstock route more or less follows the course of the Abhainn Gil an Taillier.

The above images show modifications being made to the pre-existing concrete weir. First, the wing walls were increased with concrete buttresses. Next, a specially designed steel framework was bolted-on to house the 3 metre Coanda screen. The images show the progression from start to finish.

At the same time construction works began on the turbine house (see images above), ready for delivery and installation of the generating equipment. Given the remoteness of shore location, the engineers at Renewables First pre-fabricated and tested the turbine, generator and control system assembly off site to reduce risk of commissioning issues. The equipment was then delivered to the Harris site in one trip (see images below) and then installed at the site in one go.

Renewables First was involved at all stages of the scheme development, including the feasibility and design works, as well as project managing the installation phase. The main Contractor was Duncan MacKay & Sons, hired for their local knowledge and expertise installing other hydropower schemes in the area.

The hydropower scheme is expected to generate 400 MWh of electricity per year which is sufficient energy for 99 average UK homes contributing an emissions saving of 183 tonnes CO₂ per year.