Skip to content
Case study

Carbon savings at National Grid's Wimbledon substation

20 June 2017

This case study explores how National Grid factored in environmental targets into its tender process, delivering both substantial cost and carbon savings.

Carbon savings at National Grid's Wimbledon substation
4d modelling was used to reduce the number of piles in a substation foundation by 17%

In February 2011, National Grid kicked off a major seven-year project to upgrade the cables and wires underneath London, tunnelling deep underneath the capital to meet ever-growing electricity demand. To support this new infrastructure, the business is also building new substations and upgrading existing ones along the route.

As with any construction project, the Wimbledon substation replacement comes with the usual time and cost constraints, and the absolute requirement to adhere to the highest safety standards. So far, so routine, until you put the build into context, in one of the most populated areas of the country. On top of that, the business knew it had to and could reduce the environmental impact of the construction, with a potential cost saving to boot.

Project details

Location: Wimbledon
Value: £102million
Date of completion: phase one in September 2018, phase two in December 2022
Duration: 7 years
Client: National Grid
Contractor: Laing O’Rourke
Project manager: Ian Lammin
Challenge summary: upgrading a substation in a densely populated urban environment – safely, on time, to budget and while reducing our carbon impact
Challenge solution: factoring environmental targets into the tender process resulted in carbon and cost savings

The problem: reducing environmental impact in a densely populated location

The 275kV air insulated substation (AIS) at Wimbledon is being replaced and upgraded with a 400kV gas insulated substation (GIS), made up of 16 bays and 10 items of wound plant. The project is split into two phases. The first phase will be completed in September 2018, commissioning four items of wound plant and the 16 bays of the GIS. The second phase, constructing the remaining six items of wound plant, will be commissioned by December 2022.

Unique tender feature: carbon weighting included

Wimbledon is the first tender at National Grid to include a weighting on carbon. Laing O’Rourke was awarded the winning bid, which demonstrated a 23% carbon reduction and a ~ £3m cost saving. The carbon saving is the equivalent of taking 7,600 cars off the road for a year. So not only could the environmental targets factored into the tendering process reduce the project’s carbon footprint, a focus on sustainability made financial sense, bringing more value to customers and the end consumer.

Improvements to the design from optimising for carbon

Modifications to the substation design have made the build more efficient and resulted in carbon savings. Huge savings in sulphur hexafluoride (SF₆) were achieved through use of more efficient equipment. 17% fewer piles have been used in the foundations of the substation, and the gas insulated substation building will have a 17% smaller footprint. Firewalls were reduced from 15 to 10 during design challenges leading to reduction in material use and carbon footprint.

Results: more efficiency, less to build and carbon savings

Specifically, the carbon reduction based on the tender design will come from:

  • Selection of compact GIS kit, reducing the volume of SF₆ onsite and the overall building footprint, and removing the cladding at the base of the GIS
  • Reducing the number of piles used, and changing the pile design, removing pile caps
  • Reducing the number of firewalls from 15 to 10
  • Using cement-replacement concrete
  • Sourcing recycled steel for reinforcements and kit frames, offering the same engineering strength with lower carbon manufacturing
  • Designing out skidway beams and associated civil elements
  • Using fewer cable troughs in phase two of the construction programme
  • Reusing aggregates arising onsite wherever possible


Factoring in environmental considerations as part of the tender process for construction projects means sustainable practices are baked into the work. This not only reduces the carbon footprint of the build, but can also result in significant cost savings.

National Grid’s pledge to use carbon in investments decisions

National Grid will include carbon as part of evaluation criteria in tenders where there is significant potential to save carbon and as part of its criteria on major projects, to enable the business to build and maintain a sustainable network for the future. The organisation has put an ambitious target in place, to put an internal price on carbon used in all investment decision-making on major projects by 2020.

  • Nicky Conway, Sustainable Development Manager
  • Ian Lammin, Lead EPC Project Manager at National Grid