What size generator is needed for a construction site?

Industrial generator sizing

For generators to run efficiently in commercial or industrial settings such as a construction site, it is extremely important to get the size of the generator right. When you rent a generator from Aggreko, the package we could offer you may differ from your initial request, as we take into account multiple factors to size a generator to deliver the best results for the environment and the bottom line.

Why would a generator be oversized?

There could be a number of reasons rental companies offer oversized generators, for example, to accommodate for motor starts, pump starts, and in general start-up currents; when the actual load or start-up is not known; or because a safety net or error tolerance has been added to cope for any unknowns. As a result, the customer would face higher rental and transport costs, as well as increased fuel usage and noise levels. It is not uncommon for hired equipment to run at less than 30% load meaning it is inefficient.

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What size generator do I need?

We aim to design solutions where the equipment is running at 70% load or above regularly – this arrangement can offer significant savings in fuel, carbon and local emissions.

To achieve these results, we offer the following solutions:

Load on demand – to deal with variable loads.
Flywheel technology – to help cope with start-up currents.
Battery hybrid technology – to minimise the runtime of the generator and to cope with startup currents, or as a spinning reserve.
Telemetry – Aggreko Remote Monitoring for accurate commercial generator sizing and to refine generator’s capacity to give optimum performance.

Load on demand

Load on demand power solutions replace a large, constantly operating generator with a group of smaller generators that can power up or down automatically according to demand onsite. For instance, if a site requires a total peak output of 1500 kVA, it is possible to use three smaller 500 kVA generators together to achieve this output when the site is operating at full capacity. When the demand for power fluctuates and this reduces to lower than 500 kVA, two of the generators can power down when not required.

By having two generators powering down, construction sites employing load on demand power systems can save money on the fuel that is no longer wasted through a large generator constantly operating at full capacity. On top of this, reducing the number of generators in operation during periods of downtime means harmful emissions are reduced as well as noise pollution.

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Sizing generators to accommodate for high startup or peak loads

Generator sets are typically sized for peak loads, however, most of the time they run at low load factors. As such, this results in poor fuel economy and high emissions. There are two options to improve the efficiency when facing high start up or peak loads; a mechanical solution and a chemical solution. Each option has different benefits and offer more efficiency when powering a tower crane.

Mechanical solution – flywheel technology.

Connecting flywheel technology to a smaller generator set levels the peak loads that the generator has to deal with. The flywheel system delivers high power energy during an increasing load step, capturing excess energy during a decreasing load step.

Chemical solution – smart battery hybrid system.

This solution sees a smart battery hybrid solution connect to a smaller generator. Similar to the mechanical solution, the battery output will combine with the generator output to cope with the peak loads. The hybrid will then switch off, leaving the generator running at a more efficient load (circa 80%). With the smart battery hybrid solution, it can manage the power output entirely. As it can run solely on the battery at very low loads, it allows users to gain extra efficiency, as the generator is switched off completely. This provides additional fuel, carbon and local emissions savings.

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How to size a generator for a tower crane?

Option 1: 320 kVA generator. Typically works 10-50% of the time on a fluctuating load and idle at nighttime. Very inefficient fuel consumption.
Option 2. 200kVA generator and flywheel - Enables a downsized generator for each application. Reduction of up to 45% in fuel and emissions.
Option 3. 200kVA generator and battery Generator switched off during periods of low load. Reduction of up to 65% in fuel and emissions.

Not sure what size generator do you need for your application?

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