Decarbonising Water Treatment with Scottish Water

Scottish Water takes “exciting step” on road to net zero with solar and storage first

Vanadium redox flow batteries to reduce waste water treatment site energy costs by 40% and accelerate progress towards ambitious net zero targets 

Updated with new images October 19, 2021.

Scottish Water has started work to install its first combined solar power and battery storage facility near Perth’s Waste Water Treatment Works at Sleepless Inch on the River Tay.

The £2 million project is the largest single solar energy investment announced to date by the publicly-owned water company’s commercial subsidiary, Scottish Water Horizons.

Yadlamalka will be the site of the largest solar-powered flow battery in Australia

Invinity VS3-022 units at Scottish Water, Sleepless Inch on the River Tay.

Solar-powered water treatment

The renewable energy generated is expected to provide around a quarter of the electricity needed to treat water that has been used by customers all over the city, enabling it to be safely returned to the environment. 2,520 solar panels will be installed on land adjoining the treatment works, with a combined generating capacity of just over 1 Megawatt (MW).

It will be the first Scottish Water solar project to include battery storage, in the form of four vanadium flow batteries (VFBs), capable of storing up to 0.8 Megawatt-hours (MWh) of energy. The project is being developed and constructed by Scottish renewable energy solutions specialists, Absolute Solar and Wind, with the batteries supplied by manufactured by Invinity Energy Systems.

“Perth’s waste water treatment works at Sleepless Inch is a key site for Scottish Water, serving customers across the city. By installing energy storage, we can go even further in our use of self-generated renewable power, while also supporting the operation of the wider electricity system. 

– Donald MacBrayne, Business Development Manager, Scottish Water Horizons


The inclusion of battery storage will enable around 94% of the renewable power generated to be used on site, with the flow batteries charging from renewable electricity produced when the sun is at its peak and then delivering it to the site when it is most needed, any time of the day or night.

By using this solar power on site instead of exporting to the local grid, the treatment works will cut its carbon footprint by around 160 tonnes of CO2 per annum – the equivalent of offsetting 580,000 miles from the average passenger car. It will also help to reduce energy costs at the site by approximately 40% on an ongoing basis.

Graphic: Key project facts 

 In addition to the new photovoltaic panels and batteries, Scottish Water Horizons’ project will also include installation of electric vehicle charging facilities to support the transition of the company’s 1,600-vehicle fleet of vans and tankers away from fossil fuels towards clean electricity. The site is located close to the M90, at a key hub of the transport network.

“Congratulations to Scottish Water for transforming this facility in Perth. I hope it helps the city reach its goal of becoming the most sustainable small city in Europe. By opting for renewable power they are providing a great example to other companies and public sector bodies.”

– Roseanna Cunningham MSP, Environment and Climate Change Secretary

“Innovative projects like this not only help us reach our goal of zero emission by 2045 but also help to support the Scottish manufacturing industry, the creation of green jobs and a green recovery from COVID-19.”

Commenting further on the announcement, Tom Newell, Managing Director at Absolute Solar and Wind, one of Scotland’s leading renewable energy project developers, said:

We are delighted to have been chosen as the Principal Contractor for the renewable energy scheme at Perth Waste Water Treatment Works. This will be Absolute’s 19th project constructed for Scottish Water Horizons and the first to feature a combination of solar PV, vanadium flow batteries and electric vehicle chargers. We look forward to working with both Scottish Water Horizons and Invinity Energy Systems during the delivery phase.”

– Tom Newell, Managing Director, Absolute Solar and Wind

Scottish Water Horizons has already delivered 46 solar power projects, as well as 20 wind projects, two biomass projects and a waste water heat recovery project. Scottish Water also hosts significant additional renewable generation capacity on land that it owns across Scotland.

“There are two elements that demonstrate with crystal clarity the requirements for a sustainable future: clean air, and clean water. Invinity are excited that Scottish Water has taken a pioneering step towards showing how waste water treatment can be delivered using clean electricity. We look forward to proving that vision, and to exemplifying through this project how our vanadium flow batteries can be a critical part of sustainable infrastructure in Scotland, the UK and beyond.”

– Matt Harper, Chief Commercial Officer, Invinity Energy Systems

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