Your View

Balancing the wind power debate

There is one key word missing from Mario Donnetti's sincerely held views on having many more intermittent wind farms onshore to lower energy costs and move faster to decarbonisation (NCE, last month). That word is democracy. It is built into the fabric of our society and national and local politicians ignore people's views at their peril.

Regarding carbon-free energy, my own view is that the holy grail for us conventional greens is harnessing the power of the sea. The moon moves billions of tonnes of seawater back and forth throughout the world 24/7. The challenge is to tap this immense power source economically and to be visually unobtrusive.

John Franklin (F), [email protected]

I hope Mario Donnetti was not entirely serious with his letter on wind farms (NCE, last month). If he was, I am worried on two counts.

Firstly, that he would return to an old fashioned view of an engineer as one who thinks he knows unilaterally what infrastructure solution is best and can decide, in this case, that carpeting the countryside with huge wind turbines is the only way to fight climate change. I thought we were urged several presidents ago to avoid such arrogance and that we should always consider not just the narrow technical solution, but its social, environmental, cultural and community implications. I do not see those aspects addressed.

Secondly, using wind energy is certainly a major factor in the phasing out of carbon energy sources and personally I am in favour of it in the right place and scale. But it is only one source of green energy and, as we all know, it is fundamentally flawed – it is not there all the time and is variable when it is.

National Grid electricity generation records for 2022 (not including December figures) show that gas is unfortunately still needed. There was only one month where wind was supplying more electricity than gas.

There have been headlines recently that wind was supplying 52% of UK need. But that was just for one day in October. When December figures are added, they will show that the week of high pressure and early winter weather produced little windfarm electricity and that several days were below a 10% contribution. Winter high pressures are common.

More windfarms will undoubtedly increase the energy contribution when the wind blows but will do nothing in the calm periods, so other generators are needed. There is also a recent forecast that wind will reduce globally as the climate changes and stabilises.

So I do not accept a suggestion that thousands of wind turbines, now up to 250m in height, across our landscapes would be a silver bullet to defeat climate change and that we should not complain about them.

Wind energy is one of many successful changes that have been instigated in the drive to carbon net zero and it is now gathering pace, particularly offshore. However, the pros and cons must be carefully weighed. For me, Donnetti's proposal is rather more like an Extinction Rebellion extreme.

Vic Warren (M), [email protected]

The article on Germany's electric roads system (ERS) trial (NCE, December 2022) praises the benefits of overhead cables for charging HGVs. It also appears to see an ERS as a panacea for the pollution and carbon problems in relation to road traffic. But the article fails to pose, let alone answer, any questions about the problems which may be encountered should the system be introduced in the UK.

What happens when high winds are forecast? We know that overhead line electrification fails at times of high winds and trains are stopped.

It is inevitable that the same failures will occur on the equipment repurposed for an ERS. If live wires fall onto a live motorway full of cars and HGVs, there is a high potential for fatalities. Should we close the motorway before high winds because the risk is too great? The chaos caused will not go down well with the travelling public, bearing in mind these environmental events are becoming more frequent.

I think it is too late now, but surely the National Infrastructure Commission and ICE past president Sir John Armitt should have had the foresight to campaign for new rail links – dedicated to freight – in place of High Speed 2. We should also consider new roads dedicated to freight which could use autonomous HGVs using an ERS.

Frank Marples (F), [email protected]

The failure of what I perceive to be incorrectly built Cornish hedges alongside the new A30 works between Carland Cross and Chyverton (NCE online, 23 November) seems to indicate a lack of knowledge or sufficient consultation and the collapses have caused much concern not to say derision in the local press.

For those from "up country", a Cornish hedge is a double-faced dry stone wall with curved sides which are wider at the base and which taper upward. The interior is filled with soil and rubble and the top either turfed or left to nature to provide growth.

They have been in existence for many years as field boundaries and more recently alongside highway improvements. The nature of construction is well understood by local contractors. It is important that the stone is large enough and doubly important that at no point is the stonework vertical, the stone being laid with an inward slope. There is also a limit to the height to which they can be practically built, partly based on stability but also on the height to which the stone can be lifted from the ground.

When I worked for the former Cornwall County Council, there was a standard drawing of a hedge and most of the work was carried out by a limited number of local specialist contractors. While I think it is praiseworthy that a body as august as National Highways has attempted to treat the boundaries of the new road in sympathy with Cornish tradition, it seems to have backfired. It is to be hoped that, when rebuilt, the hedges will be "proper".

Steve Burstow (M), [email protected]

Do warm mix asphalts really deliver on carbon savings?

There have been significant moves recently to increase the use of warm mix asphalts (WMAs) instead of traditional hot mixed products on UK roads. This followed an announcement by National Highways that WMAs are encouraged by default on the strategic road network (SRN). It was hoped that local authorities, which are responsible for 97% of the total road network, would also move in this direction.

Using WMAs reduces the carbon emissions by up to 15% and some major suppliers have switched to WMA as standard or the norm across their product range. With assurances being given of no reduction in the integrity or lifespan of these materials, this may appear an attractive prospect for highway authorities.

The use of hot rolled asphalt (HRA) surface course material ceased to be permitted on the SRN in 1999 with the publication of the then Highways Agency specification HD 36/99 and the switch to thin surface course materials. Ending the use of HRA and surface dressing on the SRN led to many local highway authorities following suit.

These decisions came despite the Sustainable Use of High Specification Aggregates for Road Surfacing in England report for the government in 2004.

It warned that there were limited resources of good skid and wear resistant aggregates.

The report raised concerns that the vastly increased consumption of such material arising from the switch meant resources would run out within 15 years unless local authorities adopted more sustainable road surfacing policies.

In my experience, as a former county divisional surveyor responsible for the maintenance of the local roads network and the SRN, HRA can typically achieve a 30 year life on the vast majority of the network before subsequent maintenance is required. That is up to three times that of the 10 to 20 years assumed in the current guidance for thin surface course materials on local authority roads.

So the 15% reduction in carbon emissions resulting from use of WMA bears poor comparison to the use of HRA in terms of its whole life.

I would argue that a return to wider use of HRA and surface dressing as a preventative maintenance would be of benefit for carbon reduction.

It would also minimise whole life costs, reduce the pothole plague of recent years and maintain good skid resistant roads.

Frank Bedford (M), [email protected]

Like what you've read? To receive New Civil Engineer's daily and weekly newsletters click here.