Energy use in the transportation of building materials as well as on-site processes is considered to be a major emitter of greenhouse gases on construction sites (Kanafani et al. 2023). Fossil fuels are used for heavy transport and construction machinery. Many on-site processes, such as heating, drying and ventilation, are based on fossil fuels. In addition to carbon dioxide emissions, the combustion of fossil fuels results in more localised air pollution and noise.
In the Nordics, the main measure in curbing emissions from construction sites is the introduction of emission-free and carbon-neutral energy sources. There is a focus on the battery electrification of machinery and transport, and to some extent, biofuels are also used. Biofuels and district heating are promoted for heating.
The first action in reducing energy-related emissions is to use less energy. This translates to improved energy efficiency as there is less energy used per unit of built area or volume. This is often very simple and cost-effective, especially if planned during the design phase or implemented by way of improved management. The efficiency of machinery and other equipment that uses energy can also be improved.
Where energy is used in construction, it should be emission-free or at least carbon-neutral. Emission-free energy options are emerging for transport and on-site machinery. Nevertheless, barriers remain, such as price and lack of infrastructure. Questions such as "Is there enough energy for a big construction project to use only electric machinery?" and “Can we make sure that a grid connection is in place before construction work starts?” are increasingly being asked in the Nordics.
4.1 Energy efficiency
The transport of building materials could be more efficient. Although there is limited literature on this subject, private stakeholders are finding ways to reduce transport to lower costs. The same approach can be applied in the planning and design phases of a construction project.
It is well known that public transport systems are more efficient than cars for the movement of people. Systems for material logistics probably use similar methods on a larger scale. There might, however, be opportunities to optimise the distribution of materials to construction sites and the transport of waste from sites.
As with the transport of materials to and from sites, improved on-site logistics and other changes can reduce energy use during construction (Norwegian Environment Agency 2023). A large part of on-site energy use stems from moving materials. Heating, drying, and lighting are also major energy consumers. There is the potential to reduce energy use in these activities, although there is uncertainty around how much.
4.2 Clean energy carriers
Fossil-free and emission-free construction sites use technologies that were first developed for road transport. Consequently, research in renewable energy for transport benefits the construction industry directly. Stationary power generation on construction sites uses similar technologies as in transport. Diesel generators on construction sites have the same engines as the machinery. Battery technology is already making its way into the construction industry with trucks and machines available in electric versions. However, the high upfront cost and limited usable range are drawbacks of battery technology. Smaller machines and trucks, especially on short transport routes, can benefit from this technology. Biofuels remain an option for fossil-free construction sites. This energy carrier is very efficient for heating and can be useful where electricity for charging is not available and in order to utilise fleets of older equipment. Hydrogen is also now becoming a viable fuel in transport, both by way of fuel cell technology and in modified combustion engines (Norwegian Hydrogen Forum 2023; Sadik-Zada et al. 2023). Hydrogen vehicles and machinery alleviate the range limitations of battery technology. Hydrogen is considered a promising fuel for large trucks and machines as well as for stationary power generation.
The construction industry can benefit from the development of new technologies for transport, as has been the case with the battery electrification of construction machinery. Equipment manufacturers are actively increasing their offering of battery-powered machines, as well as trucks for transportation. The development of hydrogen trucks for long-distance goods transport will directly benefit construction. The integration of hydrogen technologies into construction machinery should be investigated, based on experience from battery conversions.
Biofuels are being developed further, with sustainability issues being addressed by way of second-generation feedstock. This addresses the shortcomings of first-generation feedstocks such as vegetable oil that compete with food production and are not grown sustainably. Biomass, such as waste from forestry and agriculture, could become important feedstock for sustainable biofuel production. This is, however, a very limited resource compared to the demand for renewable energy. Advanced biofuels are typically produced as drop-in fuels and therefore this is a potential short-term solution for utilising existing vehicle and machine fleets on fossil-free construction sites.
Synthetic fuels made from green hydrogen and carbon dioxide, also known as electrofuels, may be used in the construction sector. Methanol is the first electrofuel to be commercially produced (`CRI - Carbon Recycling International’ 2022). Although synthetic diesel would be most suitable for the construction sector, uncertainties remain regarding its price and availability.
New technologies come with new challenges and research should also address this. Nordic construction sites may present harsh conditions that put stress on battery and fuel-cell systems. With the rapid growth in battery-electric vehicles, comparable growth in battery recycling will soon be needed. Unforeseen problems may appear, making it important to continually gather and share knowledge in the industry.
4.3 Infrastructure for clean energy
The distribution and storage of new forms of energy calls for new solutions in infrastructure. Construction sites that use battery-electric machinery may easily overload existing utility systems. The production, storage, and distribution of hydrogen require new infrastructure.
With the advent of battery-electric trucks and on-site machinery comes the need for charging. Large construction machines such as excavators require powerful charging stations on the site itself. The electrical power supplied to the site may not be sufficient for charging, or several parallel construction projects in an area may overstretch the local grid. This problem could be mitigated by way of a combination of solutions. Trucks are not restricted to charging only on the construction site and can be moved to dedicated charging points if the on-site supply is overstretched. Work can be scheduled so that charging is distributed over longer periods to limit power peaks. On-site stationary power packs are becoming available and can be used to distribute power use over time (Big Buyers Initiative 2022; Eric Rambech, Rebecca Briedis, and Sigrid Møyner Hohle 2021).
Green hydrogen production via electrolysis is an established industry, and therefore distribution and refuelling in the construction sector is a primary interest. Hydrogen for vehicles is now typically supplied to refuelling stations in high-pressure cylinders. Hydrogen can be transported to construction sites in the same manner. On-site storage and refuelling is, however, a new technical challenge.