SSEN avoids carbon emissions equivalent to powering 500,000 homes for a week, through a smarter energy approach

Scottish and Southern Electricity Networks (SSEN) has successfully utilised low-carbon energy generation on Islay, to avoid 2,450 tonnes of CO2 emissions, and save customers £230,000 in the process. This marks an important milestone for the UK energy system, as low-carbon technology has supported system security in an economically viable manner on the islands of Islay, Jura and Colonsay. 

Constraint Managed Zones are an alternative to traditional generation being used when the main electricity network is temporarily disconnected, for example during a prolonged power cut, fault on a subsea cable or during a period of network maintenance. Rather than rely solely on diesel generators or back-up power stations, the use of renewables and energy storage is being encouraged to keep the power flowing for local communities until the traditional electricity supply is back up and running.

Since October 2019, SSEN has drawn from its CMZ on Islay, providing a low-carbon solution to avoiding network reinforcement. This has avoided the equivalent carbon emissions of powering half a million homes for a week, while also avoiding the cost of traditional network reinforcement which would have been in excess of £230,000.

While SSEN teams were progressing plans to replace the subsea cable between Jura and Tayvallich on the mainland following a fault in November, 40% of the average local electricity demand was met by the Inver Hydro Power Station on Jura, working alongside the long-established Bowmore Power Station to ensure customers on the islands continued to receive the power they need.

Stewart Reid, Head of Future Networks at SSEN welcomed the announcement:

“The proliferation of low-carbon technologies is creating more opportunities to take a low-carbon approach to addressing network constraint. Managing our energy system in a smarter way helps decarbonisation efforts in a cost-effective manner for the communities we serve.”

SSEN strongly supports the UK and Scottish Governments’ 2050 and 2045 respective net zero emissions target and will have a critical role in supporting the low-carbon technologies that will enable these targets. SSEN is transitioning from being a Distribution Network Operator (DNO) to a Distribution System Operator (DSO) to assist in managing more complex relationships within the energy system, and to maximise opportunities for the communities it serves.

Stewart continues:

“Through utilising the CMZ we have managed to avoid the carbon emissions equivalent of taking 971 cars off the road for a year, or enough to power half a million homes for a week. Our ambition is now to increase CMZ usage across both our distribution areas, to deliver cost savings and significant carbon reductions.”

The constraint on Islay was addressed through the Inver Hydro scheme based on the neighbouring island of Jura, whose 2MW installed capacity was able to meet 40% of the average local load and provide nearly 5GWh of renewable energy during the recent fault scenario.

John Lithgow, Managing Director of Inver Hydro said: “The CMZ has been a great success, ensuring we made a significant contribution to keeping the islands’ lights on over the winter with low-carbon generation. It clearly demonstrates the role of embedded generation like small hydro in delivering the integrated energy networks solutions of the future.”

For more information on how you can get involved in supporting system security, and the UK’s net zero ambitions, please visit

To read more on the recently completed Jura – mainland submarine cable replacement project, click here.