On construction sites around the world, diesel generators are used to provide short bursts of power to heavy equipment. To get to zero emissions, these sites must find new ways to meet peak power requirements.

How do you calculate the power requirements of a construction site? The traditional method has been to start with the biggest bits of kit on site. That’s often the tower cranes. You would check the maximum power recommended in the manual for each crane. You’d typically find it would need a few hundred amps of power.  

On most sites, this level of power won’t be available off the grid. Instead, you’ll need a generator. So you round up the power requirements for each crane, to match that of generators available to hire locally.

Then you’ll place a generator close to each crane. And maybe another for welfare cabins and general site requirements. Some more for construction hoists. And a bit of overhead, just in case. So now, on a site with three or four cranes and three or four construction hoists, welfare cabins, and other electrical equipment, you have multiple diesel generators each pumping out carbon dioxide, along with other emissions.

But these generators are only working in short bursts. As a crane operator pushes the lever to raise a load, a surge of power is needed to overcome gravity. But once the load is moving, this requirement drops.

For most of the lift, nowhere near this top level of power demand—peak power—is needed. And for most of the day, that diesel generator is just being used to keep cab lights, controls and air conditioning running.

It’s like charging your phone each night by plugging it into your car USB and driving around until it’s at 100%.

But what if you could just supply the average power needed across the site? If you could store the electricity coming into your site, and then release it in short bursts as it is needed, you could power the entire project, with just a few amps from the grid or a renewable energy source.

Achieving this would allow sites anywhere to work without generators. That would enable full electrification of most construction equipment. It would slash the impact of the building industry on climate change. And it would save designers and project managers all of the hassle that comes with laying thick cables, or fuelling up generators.

But it would require forms of energy storage that could be slowly charged, and could then release intense levels of power, in an instant.

An AMPd Enertainer, on site with Select Plant Hire

Peak power, without emissions

Steve Bradby is technical lead for Select Plant Hire in the UK. The company is part of contractors Laing O’Rourke. It’s one of the leading suppliers of tower cranes in the UK, and supplies some of the largest units: giant luffing jib cranes, suitable for lifting heavy pieces of steel and prefabricated concrete modules. 

The tower cranes Select supply are electric, but demand more power than is supplied on the grid. And that poses a major stumbling block, as the company aims for zero emissions on its site, says Bradby: “When I look at tower cranes, and see them being paired with generators, I think it’s an absolutely dire thing.”

Most of Select’s fleet will work from mains power. But not all of them. “We see 10 to 20% of the fleet on generators,” says Bradby. “Often they’re on a generator at the start of the job because there’s a delay getting power to site, and occasionally there simply isn’t the power throughout the job. The bulk of our fleet is over 24 tonne capacity, a substantial amount is over 32 tonne capacity, and some of it is over 66 tonnes of capacity. Which in the tower crane world is big. So therefore their power demands match that: it’s big.” 

The biggest tower cranes Select supplies are luffing jib tower cranes. These are typically used in city centres. They feature a jib—the arm extending out from the crane—that pivots up from the superstructure. The lifting rope runs up the jib, with the hook hanging from the rope, over the jib tip. That allows them to lift up higher than the cab, and to work without moving over neighbouring sites.

Some of the largest of these cranes are Terex CTL 1600-66’s. These can lift 66 tonnes when the jib is raised to work at its minimum radius  A crane’s capacity decreases, the further away the load is from the mast. But one of these cranes can still lift 16 tonnes with its 75 metre jib fully lowered. That’s plenty, even for modern construction techniques that use large prefabricated beams, panels, and even volumetric modules.

To make those big lifts, the manufacturer says that the crane will need around 400 kilovolt-amps of power. It also uses power to raise the jib, using winches and ropes; and to turn—or slew—the crane, using electric motors to turn the ‘slewing ring’, essentially a big gear at the base of the upper structure.

“You’d see anything from 300 to 650 amp power supply required,” says Bradby. “And obviously with that, not only do you need the power from the street to come in, to deliver those peaks, but also you need cables and the cables can be huge, and they have to be dragged around site.

“On one of the big cranes, a 66 tonne luffer, the requirement from the manufacturer says it would need a 650 KVa generator. Now 650s don’t really exist, they aren’t readily available, so the nearest size that we can pick up is 800Kva. So we’ll stick an 800 KVa generator powering this crane.”

That oversized generator burns a lot of fuel, costing money and contributing to emissions. “Assuming that that crane was working for 60 hours a week, over 50 weeks, a standard 800 kVa generator will be costing you—with fuel—around £230,000 to run your crane.”

But that 800 kilovolt-amp generator isn’t working all day. It’s mostly just working when the operator first pushes a lever to move the crane, or to hoist a load.

“Every time that the operator goes to start a mechanism, there’s a sudden surge in demand,” explains Bradby. “It’s exactly the same as accelerating from the traffic lights, your power requirement to get the vehicle moving is substantial, and drops off very quickly.”

Select needed a way to ‘average out’ the power on site: systems that would release a surge of power, just for those few seconds when it is needed, but which could be charged slowly using a small generator, or a mains supply.

“We’ve headed down two routes with the tower cranes, says Bradby. “We’ve got Punch Flybrids, and we’ve also got the AMPd batteries from Hong Kong. There are slightly different applications for the two. But the outcome of both is phenomenal.”

The two systems Select uses are based on very different technologies. Punch’s Flybrid is based on a flywheel. A power source sets a mass spinning, in a vacuum sealed box. When a surge of power is needed, this is drawn from the flywheel. For a moment, the flywheel slows its spin. But then, using a trickle of electricity—directly, or transferred via mechanical or hydraulic means—it picks up speed.

The Enertainer, from AMPd, is essentially a bunch of batteries in a container. Increasingly, companies are offering mobile or modular battery packs like this, which can be used for general power requirements on site. These, however, generally only have low power outputs. AMPd’s Enertainers are designed less for their overall storage capacity, and more for their multiple high power outputs.

Spinning up power

Punch Flybrid started developing its technology far from construction sites. “Originally, we developed the flywheels for motorsport,” says Tobias Knichel, MD of Punch Flybrid. “A Formula One or Le Mans car has a highly dynamic duty cycle with very high power events that occur very frequently in a short period of time. And this is where flywheel can play to its strengths.”

As Knichel explains, it is on equipment with highly dynamic duty cycles—a crane, a racing car—that flywheels demonstrate their benefits. “The Flybrid unit comes from the realisation that it will become more and more unacceptable to waste energy, no matter where that energy is coming from. Dynamic duty cycles waste a lot of energy. By dynamic duty cycles, we mean powertrain profiles for powertrain that require high peak powers, but have quite low average power. Traditionally, that requires you to size the powertrain for the peak requirement, and means that if the average power is low, that you have an oversized powertrain that you carry around, that you have to fuel and that ultimately is less efficient than if you were to be able to size the powertrain more on the average load.”

A flywheel helps designers of sports cars, or construction sites, to focus on those average power requirements, not peak requirements. “If you could have an energy storage system that can deal with the spikes in the load, then you can have that scenario where you can size the main power train more around the average load,” says Knichel. “A chemical battery always has much better energy density, both volumetric and also in terms of weight. And a chemical battery can also store the energy much, much longer compared to a mechanical flywheel. But for dynamic duty cycles, flywheel energy storage can play to its advantages.”

Chemical batteries have a limited life cycle. They can only be charged and discharged a certain number of times, before their capacity drops. The battery in your phone may now keep its capacity for 3,000 charges, and will often outlast the phone itself. But a crane may need peak power hundreds of times a day. A racing car will draw on a hybrid system many times more.

“A tower crane, excavator, or concrete pump has many, many hundreds of cycles per day,” says Knichel. “A flywheel energy storage system is designed to do more than 10 million full charge and discharge cycles. It’s orders of magnitudes different compared to what you would typically do with a chemical battery.” 

The core components of a flywheel system aren’t anything new: they’ve been used in simple machines like potters’ wheels for centuries. In the 1950s, they were used in Munich to power emissions free buses. But these needed giant flywheels, taking up passenger places on the bus and—because they act as gyroscopes—working against the driver as they try to steer.

Punch Flybrid’s answer has been to use modern manufacturing methods to shrink the spinning mass of the flywheel, and to speed it up, says Knichel. “The Munich buses needed a 500kg cast iron flywheel. Today, with modern materials, we can make a flywheel that weighs only 5kg, but spins much faster, and so achieves the same amount of energy storage.”

Manufacturing a flywheel that is suitable for these peak power applications doesn’t take particularly novel or hard-to-source materials. But it does take clever design. “It is made out of conventional materials,” says Knichel. “Any factory that can make an internal combustion engine or transmission, has the kind of machines and the kind of processes to be able to make a flywheel energy storage system. 

“The flywheel itself is a forged steel component, housed in a cast aluminium casing. The manufacturing processes that you use to create a flywheel system are the same as the manufacturing processes for an internal combustion engine or transmission.”

Designing a system that works efficiently, and meets the needs of many very different applications, is essentially all about setting the right size mass, spinning at the right speed.

“A flywheel stores energy as kinetic energy,” says Knichel. “The inertia is related basically to the size and mass of the flywheel. The faster you can spin the flywheel, the less mass you need to store the same amount of energy. If you can spin the flywheel twice as fast, you only need a quarter of the mass to store the same amount of energy.

“This is why we can design the flywheel that can fit into a racing car, it needs to be very compact, very small. so we spin it very quickly. But we can also design it for construction sites, where maybe size and weight are not the primary considerations, but material costs, and overall purchasing costs are probably more important. And so for the construction industry, we actually have one standard size that covers everything from 100 KVa generator up to 1000 KVa generator.”

UK power specialist John F Hunt taking delivery of a series of Punch Flybrid units

Peak batteries

The origins of AMPd’s Enertainer are very different to those of the Flybrid. Where the Flybrid uses technology as ancient as the potter’s wheel, the Enertainer uses batteries: not an entirely novel technology, but one that is still evolving and is likely to continue to see rapid development.

Where the Flybrid has its roots in motorsport, the Enertainer was designed from the start for use with large tower cranes. AMPd Energy, which had previously developed UPSes, or uninterruptible power supplies, were set a challenge by the executive director of Balfour Beatty’s Asian JV Gammon, explains Hayley Arckless, UK country manager for AMPd. 

“That challenge is one that the construction industry as a whole faces, especially as we’re moving into a lower carbon environment: replacing diesel generators on construction sites. Between 2017 and 2018, we worked with Gammon to define what that case could look like. In late 2019, we had the first Enertainer delivered to a Gammon site, to power one tower crane. Since then, we’ve had many more Enertainers delivered through Gammon. They’ve been a fantastic development partner, not only to get the Enertainer off the ground in the first sense, but continuing to help us with product feedback to really tweak and define the unit.”

Like Punch’s Flybrid, AMPd’s Enertainer configures an existing technology, for the specific needs of the construction industry. “What makes us truly different is that we are a product company,” says Arckless. “The Enertainer unit is designed to act like a water tower. We constantly trickle in a small amount of input power, and the Enertainer stores all of that power, but can push out a high current intermittently, when it is needed.” 

The large tower cranes that work in a constricted city like Hong Kong, where skyscrapers are the default option for construction, are ideal candidates for use with an Enertainer.

“The base load on a tower crane is incredibly low,” says Arckless. “For around 98% of the day—minimum—that crane is running on a base load. But when it does need to lift, it demands an incredibly high amount of power. That’s why it’s incredibly difficult to remove that diesel generator. In a lot of different parts of the world, the grid is incredibly constrained. So you have to wait a long time for a connection, even if it is possible to get one.”

That doesn’t mean there is no power: rather, on most sites, the power connection cannot handle the peak demands of cranes. “We’re often able to take an existing building supply and existing connection,” says Arckless. “That’s often way too low to do anything with it in a normal construction case, but we’re actually able to take that and use it.”

Gammon used Enertainers on one project like this, where they had some power, but not enough for peak demands. The project, called ‘Advanced Manufacturing Centre’, is a 108,000 square metre building, with a seawater district-cooling system. The main cranes on site were 24-tonne STL 410s from Yongmao, a Chinese tower crane manufacturer that has focused on large cranes, and has seen considerable success in Asia and other rapidly developing markets.

“There was 400 amp power available to the site,” recalls Arckless. “But they needed over 2000 amps to power all of their equipment. Each Enertainer took 15 amps from that 400 amp supply. We could power a significant amount of that infrastructure, while also leaving quite a lot of that existing power supply spare. They reduced their carbon footprint by 81%. And those metrics are really around removing that constantly burning diesel for generators.” 

The Enertainer has been a runaway success in Hong Kong, and in other markets. AMPd now has over 200 units deployed around the world. In Hong Kong, more than 40% of sites use the high performance battery packs. Based on that success, AMPd started looking at new markets to enter, and identified the UK as one where there would be high demand. AMPd’s first customer was Select Plant, Bradby’s company.

“They have always been quite a pioneer when it comes to new technologies,” says Arckless.  “They always seem to be on the first foot, it really made sense for us to partner with them. They saw the value in this right away. And they had a long list of customers who they thought this could really be relevant for.

“The very first project that they suggested was one of their own, the Olympia redevelopment, one of the largest construction sites in London. They took three units in late 2022. We’ve had nothing but positive feedback so far.”

Bradby was part of the team at Select that gave AMPd that first break into the UK market, in Olympia. He’s a big fan of Punch’s Flybrid, but sees even more scope for carbon saving when this is combined with Enertainer high power battery storage. 

“With the batteries, we can save even more,” he says. “The Flybrid’s working really well, it’s brilliant. If you have power, but not enough, or if you don’t want to run 250mm cables halfway across site, then the battery is phenomenal because—as we’ve seen with the batteries at Olympia—they’re running on about 20A.”

Charging forward

Select’s vote of confidence in the system, helped AMPd to win new customers in the UK. It showed that some of the toughest sites in the country could run huge cranes without generators or a high power temporary grid connection. And that helped Arckless pitch the batteries to another customer, Bowmer & Kirkland. The company is now one of the biggest users of Enertainers.

Bowmer and Kirkland are a UK contractor, who have been in operation for over a hundred years. They work on sites across the country, using equipment hired in from other suppliers. 

Dave Shooter is their plant manager. “I’ve been with Bowmer and Kirkland since 1995, when I started as an engineering assistant or ‘chain lad’ as it was known in those days. I worked my way through to project manager, working on high rise sites in city centres.”

That gave Shooter a real sense of the logistical demands of running large fleets of tower cranes, and of the financial costs. “We’re running around 20 tower cranes at any one time. We’ll have about the same number of construction hoists, and around 200 mast climbers. We don’t purchase any plant, we hire in from specialist companies.”

Bowmer and Kirkland have been using both Flybrids and Enertainers, and are now looking at how these can be used together. Dave first learned about Flybrid from power system supplier Lee Stewart of Stewart Energy.

“We were introduced to the Flybrid guys just out of the Covid lockdown. We ran some trials of it with tower crane manufacturer Wolffkran, one of our suppliers. The Flybrid knocks out that peak power requirement.

“We projected we would be making a reduction in generator size of around a third, to 60% size. We very quickly realised that we could actually drop that to 50%, halving the generator capacity.”

Shooter saw how the Flybrids could be used to smooth the peak power requirements of tower cranes and other equipment. And he’s been running the Enertainer too, achieving huge fuel and carbon savings. 

“We’ve got a site in Stoke, it’s got two 24 tonne cranes on it, which would have both required a 500 KVa generator,” explains Shooter. “If we’re working a 55 hour week with those cranes—and I’m being conservative here—we’d be burning 25 litres of fuel an hour.

With two of those generators for 52 weeks, that’s more than 200,000 litres consumed over the year. In carbon terms, that’s 374 tonnes of carbon over a year.”

Shooter and his team can achieve huge carbon savings—as much as 70%—just with the Flybrids. But what if you power the cranes from an Enertainer connected to the mains, rather than a generator?

“We’ve got enough power within the Enertainer unit to power two cranes [that would normally need a 160kVa generator]. The first one that we had in the UK ran two cranes off of the one battery pack and essentially we’re charging that from something that could be plugged into the back of a street lamp, like an on-street car charger.

“The unit’s capable of producing approximately 500 amps and when we’re talking about the consumption that we’re looking at, there hasn’t quite been anything until this point with that much capacity. We bring the Enertainer kit on site, and it’s just like having a 500 KVa substation, at any point on your site, that requires a minimal amount of charging.”

With storage options like this, calculating diesel requirements is a lot easier: it’s essentially zero.