Anthony Maguire, director of Longevity Power, explores how the construction industry is utilising renewable energy to achieve a net zero carbon-built environment

Traditionally, a fundamental part of a sustainability consultant’s role was to help asset managers establish their year-on-year energy and greenhouse gas emissions performance. This would involve frequently removing assets undergoing development and refurbishment from the like-for-like analysis as they would create a level of statistical noise that detracts from the overall portfolio-level energy reduction programme.

While this was a logical approach, it also fuels the idea that energy consumed during construction and refurbishment is somehow of secondary importance to day-to-day operational energy consumption. More complex to track and benchmark, there was a general lack of appreciation of what low or zero carbon construction looked like.

An increasing focus on embodied carbon emissions has put the spotlight firmly on the construction sector over the past few years. However, the operational emissions associated with the construction process itself still tend to get lost.

Granted, it is a relatively small fraction of the overall impact of the development when compared to the lifetime embodied carbon of materials such as steel and concrete. However, the emissions associated with power tools and lighting to forklifts and security systems can be considerable.

Furthermore, during the early phases of any construction project, access to a grid connection can often be challenging, which can lead contractors to turn to diesel generators that have a very high carbon intensity, and also come with NOX, particulate matter and sulphur dioxide emissions.

Providing a ready alternative is not straightforward. Erecting temporary onsite renewable generation is rarely practical owing to cost and space constraints. However, there are several measures that can have a significant impact on reducing the CO2 emissions associated with the construction process.

Hybrid generators

Construction sites often have very high peak loads at particular points in the process, far in excess of the maximum electricity import capacity of the site itself. Contractors, therefore, have to install diesel generators that can deal with these periods of very high consumption. However, as they are fairly infrequent occurrences, the diesel generator is oversized for the majority of the day, which means that it is not running at a good fuel economy and emits more particulate matter. In London, for example, 14.5% of the most harmful emissions such as PM2.5 are estimated to be from stationary diesel generators on construction sites.

Companies such as Off-Grid Energy and Firefly propose the combined use of a generator with a battery storage system which ensures that the generator is always running at full capacity, charging the battery with any excess power, allowing the generator to be turned off for large periods of the day, reducing PM10 and NOx emissions by up to 50%.

Hybrid and electric construction vehicles

One incremental improvement that would have a significant impact is the efficiency of the equipment onsite. In cities like London, where there is a strict low emissions zone standard, it seems conflicting that construction vehicles such as diggers and excavators are not held to the same standard as passenger vehicles.

A movement to hybrid and electric construction vehicles would have an enormous impact on the CO2 emissions and the localised air pollution associated with construction sites.

Hydrogen fuel cells

In late 2020, the National Grid utilised a hydrogen fuel cell alongside a 216 kWh battery storage system at its construction site in Lincolnshire for the provision of all heat and power. The system uses blue hydrogen, which is derived from natural gas, and so the emissions intensity of the project is by no means net-zero.

However, it eliminates localised pollution and once there is a more reliable supply of green hydrogen, such projects could be the most feasible means of achieving net zero carbon construction sites. Construction companies are increasingly partnering with providers of hydrogen fuel cells like Mace, who have partnered with AFC Energy, and have a target to remove diesel generators from its operations by 2026.

Furthermore, off-grid hydrogen lighting solutions have emerged as a noise-free challenger to conventional diesel generator powered lighting rigs. The energy demand associated with construction lighting can be significant, as it needs to be bright enough to allow for working at night as well as for security. While upfront costs are typically higher than conventional lighting solutions, improved efficiency and lower maintenance costs can make them cost-competitive over the course of the construction project.

Carbon offsetting

Regarded as a dirty word in some circles, the reality is that the construction sector is unlikely to be able to achieve net zero carbon in the medium term without reliance upon offsets. Even with the onset of hydrogen fuel cell technology, the proportion of green hydrogen in the UK is vanishingly small as of 2022 and is only likely to ramp up significantly from 2030 onwards.

Likewise, battery storage technology is projected to see significant reductions in price which should allow contractors to pivot away from diesel generators and rely more on the electricity grid. However, the UK electricity grid will not be fully decarbonised until 2035 at the earliest and there will therefore always be a residual amount of carbon that will have to be offset in some way.

Contractors will have to ensure that offsets are measurable, verifiable, and ideally local in scope. Consultants frequently hear people espouse the virtues of investing in local tree planting schemes as a means of achieving a net zero carbon-built environment. However, according to the UK GBC best practice guidance, carbon credits with the UK Woodland Carbon Code are only valid if they are ‘ex-post’. In other words, they can only be used if they correspond to carbon offsets that have already occurred in the past, of which there are only a very small number.

In practice, construction companies looking to achieve net zero carbon through offsets are therefore likely to have to look to the Gold Standard or the Verified Carbon Standard for valid offsetting credits.

The heightened focus on carbon emissions has encouraged positive action from the construction sector and implementing these measures will help to reduce CO2 emissions considerably. However, until there are stronger regulatory drivers, the likes of hydrogen fuel cells and hybrid construction vehicles are likely to be limited to flagship projects. Creating a more robust regulatory framework in the construction industry will therefore act as a key facilitator in the drive towards achieving a net zero carbon-built environment

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