IET report weighs up grid transmission costs

Delivered in conjunction with engineering consultancy Mott MacDonald, the report found that underground AC cabling was 4.5 times more expensive than overhead lines. As an example, a typical 15 km long 5000 MW overhead line was estimated to have a build cost of nearly £40m, with an equivalent underground cable costing around £330m.

Offshore high voltage direct current (HVDC) point-to-point cable was found to be around 5 times more expensive than overhead lines, while an offshore HVDC network connecting multiple sites to the onshore grid was around 11 times more expensive. According to the report’s authors, the findings can inform policy makers, local authorities, communities and bill payers, helping them weigh up transmission costs versus other factors such as environmental impacts, delivery times and carbon intensity.

“Access to a cleaner, more affordable, more secure supply of energy requires the biggest programme of electricity and transmission network development in at least two generations,” said Keith Bell, Professor of Power Systems at the University of Strathclyde and Chair of the Project Board for the report.

“Referring to NESO (National Energy System Operator) numbers…out to about 2036 it adds up to about 80 billion pounds worth of investment, facilitating the connection of a lot of wind generation in particular.”

While subsea cabling is essential to connect that offshore wind, choices still need to be made about how that power is transmitted once it comes onshore. Overhead lines are viewed by some as an eyesore, but with subsurface AC cabling almost 5 times more expensive, siting all new onshore transmission underground would have a significant impact on both bills and delivery times.

“The current estimate is, for a typical bill, about 6 per cent of that is the cost of the transmission network,” explained Professor John Loughhead, member of the report’s Project Board and IET Fellow and Past President.

“If we're looking to the future, the transmission network is going to be much larger and a greater proportion of electricity is going to come from low marginal cost renewable sources, then you can expect that the proportion of the bill that comes from the transmission network in the future will increase. Exactly how much it increases - and what that might mean for typical people - was not something that was part of the study. But I think the extension (of the transmission network) will undoubtedly increase the proportion of the bill that is going to be due to transmission costs.”

The report updates published data from 2012 and draws on a broad range of data from manufacturers, installers, operators and other parties. Further information and the full publication can be found on the report’s web page.