12 Jul, 2023 By Domenico Traverso
Skyscrapers, traffic jams, shopping malls, and air conditioners. It is not hard to see why cities account for two-thirds of global energy consumption and more than 70% of annual global carbon emissions.
With more than half of the world’s population living in cities today – a number expected to increase to almost 70% in 2050 – we will not reach the goals of the Paris Agreement without a deep decarbonisation of cities.
What’s clear is that the battle against climate change will be won – or lost – in cities. As we build new cities to accommodate this burgeoning population, we cannot rely on the building practices of yesterday. Construction machines worldwide emit a staggering 400Mt of CO2 annually, which is equivalent to the emissions from international aviation. While it is technologically possible to electrify virtually all processes on the construction site with new machines that we have available today, electrification is not the only step we have to take, and it is not always feasible right now.
Excavators: the construction industry’s primary sustainability challenge
Take the humble excavator, the main star of the construction site, but also the main culprit in the context of emissions. Excavators account for 50% of all CO2 emissions created by the construction industry. Construction machinery and vehicles are increasingly being electrified, which is good news, but deploying a full-scale electrification of excavators today is not straight forward due to logistical and operational barriers both at construction sites and across the industry. It’s also not the best use of resources.
Compared to passenger cars, excavators need to work much harder and for much longer between charges, meaning that they need extremely large batteries to match the productivity of the diesel equivalent. As a result, fully electric excavators consume a lot of resources for the battery and are expensive to buy, so the total cost of ownership over their lifetime still exceeds the diesel machines by a large margin.
Another important consideration is that not all excavator work sites have enough charging energy to support a fleet of electrically powered excavators. Those sites that do have lots of electrical power onsite are often very big, like quarries, and require battery-swapping in the field at the beginning and end of every shift and charging those back in the depot. Given that the batteries weigh tons, this poses operational challenges.
Energy efficiency reduces emissions – even in diesel machinery
And then there is the question of green energy supply. A rough estimate says that if all the world’s excavators were electric, they would consume as much energy as is generated by all the world’s offshore wind turbines today.
Instead of only focusing on electrification of excavators, the key to decarbonising these machines is to implement energy efficient technologies that can immediately reduce the diesel use and at the same time address some of the challenges for electrification.
Today’s excavator systems operate on diesel at a mere 30% efficiency, with 70% of engine energy being wasted. There is significant potential for energy reduction by introducing measures such as variable displacement pumps, digital displacement, variable speed pumps, and decentralized drives. These technologies, along with energy recovery systems, can enhance efficiency and reduce energy consumption.
In our experience at Danfoss, some of these technologies can already deliver fuel savings of between of 15-30% in excavators over 15t while at the same time increasing the work capacity of the machines. Soon it will be possible to apply this technology on all sizes of excavators and even reach fuel savings of up to 50%.
Furthermore, these energy efficient technologies can reduce the size of the battery needed to electrify them by up to 25%, or in turn ensure that the machines can run for much longer on their batteries. This also reduces the amount of charging power, and thereby renewable energy required, to make the same impact.
Rethinking decarbonisation in construction
We see electrification as the general trend and direction for construction machinery. But we see efficiency as an enabler of this movement and a no-regrets first step to take – regardless of the type of fuel used today. Electrification can lead to emissions reductions both by replacing fossil fuel energy with renewable electricity generation, and by saving energy due to the higher efficiency of electric technologies.
As an industry, we must take responsibility for our role and be more vocal about the technological opportunities and solutions. We must take bold steps towards decarbonising the construction industry today, so that we can sustainably create the cities of tomorrow.
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