23 Mar 2021

Did You Know? Size matters when it comes to generators

Man holding engine miniature

It’s difficult to know in advance exactly how much power you’ll need for any given project or event. The situation may change on the ground. The ambient temperature may be higher or lower than you anticipated, especially if you’re hit with dramatic or out-of-season weather. You could need to scale up capacity at short notice to accommodate higher-than-expected demand. 

This makes choosing the right size of generator very tricky. 
The easy answer might be to overestimate how much power you need, and opt for a high capacity generator or temporary power substation that you’re confident will more than cover requirements. This brings a different set of problems, though.
First of all, more power generation capacity means using more fuel. If you’re underutilizing a diesel generator, the way it uses fuel also becomes very inefficient. Once you get down to running at about 10% of capacity, you’re essentially wasting up to 60% of the diesel per kWh of the energy you use. This could end up pushing you well over budget. And all for something that brings you no additional value.
To run efficiently, generators should work at 40%-80% of their capacity. If you rent a high-capacity generator but only end up using 30% of its rated capacity, this can cause the machine to do something called “wet stacking”. This is where the horsepower suddenly drops. The generator stops performing properly and you may even have to stop and replace it with a smaller one to continue with the job. The worst of both worlds, basically.
Secondly, using all that fuel means producing higher emissions. Using a larger generator than you need means you’ll be creating unnecessary waste and increasing your carbon footprint - again, with no benefit to anyone.
And then there are the safety issues that come with using generators of the wrong size. 
If your generators are too small for the power requirements of the job, the undersized generator could shut off or cause the circuit breaker to trip. The engine speed slows down, the frequency and voltage of the output become unstable, and you risk damaging any sensitive or expensive equipment that’s powered by the generator.
Or, let’s say you opt for a single high-capacity, high-voltage generator, hoping to supply power to all your equipment across a large area. That means you need to lay very long cables from generator to destination. 
By the time the electricity reaches the end of the cables, it will have lost at least 5% of its voltage, which could cause problems with the equipment you’re trying to run. Plus, of course, you have trip hazards and other safety issues from all that cabling. Much better to use a series of smaller generators, placed nearer the source.
These issues make it essential that you right-size your generators. But how exactly does that work?
Sometimes it’s a case of monitoring and gradually honing and perfecting your power generation and supply system. For example, we work closely with festivals each year to track the efficiency of all generators. We use this data to design ever-better energy-saving and fuel-saving options, and to specify perfectly sized generators for future festivals. 
For example, one year this involved monitoring 126 generators around a site, collecting over 5 million data items, and plotting real time output for each machine. From here, we figured out that the generators were, in fact, significantly oversized for the job.
To fix the problem, we created temporary power stations by stacking several smaller generators together. As the power demand went up, more generators would switch on, delivering these peak loads. As it dropped, some generators in the chain would switch off. This was a far more efficient way of doing things.
What’s more, we introduced ways to store excess energy in battery banks during low demand periods. This created an additional, sustainable energy supply that helped to meet peak surges without the need for higher-capacity generators. These had the extra benefit of acting as an uninterruptible power supply (UPS), should the generator ever shut off without warning.
This hybrid system means that the team could switch from running inefficient generators 24 hours a day for 5 days to running highly efficient generators for just 2-4 hours per day. While all the time producing the same amount of energy overall as before. 
With such pronounced fuel, cost and emission savings, it makes sense to pay close attention to right-sizing your generators before the start of a project - and to monitor their performance throughout. 
Make sure you work with a temporary utilities provider who takes a close interest in how you’ll be using their equipment, rather than simply renting you whatever generator you ask for, with no questions asked. Make sure, too, that they have remote monitoring systems in place to keep tabs on their generators and have technicians on hand to help you fix problems as they emerge. The more hands-on they are, the better-sized your generators will be.