The scheme is the utility's largest single solar energy investment to date and is the first to include battery storage facilities in its design, which will enable around 94% of the renewable power generated to be used on site.
It is the 50th solar power project to be delivered by Scottish Water Horizons, the publicly-owned water company's commercial subsidiary.
More than 2,500 solar panels are now installed on land adjoining Perth's Waste Water Treatment Works at Sleepless Inch on the River Tay, with a combined generating capacity of just over 1 Megawatt (MW).
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.
The battery storage technology will installed later this year - allowing energy to be produced when the sun is at its peak and then delivered to site when it is most needed, any time of day or night.
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This will help to cut the carbon footprint of the works by around 160 tonnes of CO2 per annum - the equivalent of offsetting 580,000 miles from the average passenger car.
Managing Director of Scottish Water Horizons, Paul Kerr, said: "This is an exciting milestone in our journey towards Scottish Water's ambition to achieve net zero carbon emissions by 2040 and it is fantastic to see how innovation is constantly increasing the amount of energy we can generate at our sites.
"The waste water treatment works here in Perth is a key site for Scottish Water, serving customers across the city, but it uses a lot of energy in serving its vital purpose. Being able to maximise the renewable energy we are now generating by storing via battery technology will be an important boost to the value of our investment - ultimately reducing energy costs at the site by around 40% on an ongoing basis.
"This year we have assessed over 450 sites for their suitability to host renewable generation and this will form a major part of how we cut our emissions in the coming years, alongside a range of other measures."
In addition to the new photovoltaic panels and batteries, the project included the installation of the utility's first rapid 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.
Cabinet Secretary for Net Zero, Energy and Transport Michael Matheson said: "This is a very welcome project from Scottish Water and marks a real turning point in how renewable energy is incorporated into sites and placed at the heart of powering Scotland's essential services. At the same time, it can be a part of Perth's bold ambition to become the most sustainable small city in Europe.
"The Scottish Government is committed to ending Scotland's contribution to climate change by 2045 and it is innovative schemes like this which will help us reach that target, as well as creating green jobs and contributing to a green recovery from the COVID-19 pandemic."
