How to Size a Generator

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Tired of being left in the dark by our national power supplier? You’re not alone! More people are investing in generators, whether it is to handle standby power requirements, or to go off the grid completely. However, an important step in the process is to size your new generator correctly. Some business- or homeowners opt for the cheapest possible generator, guesstimating that it will serve their needs, but it’s just not that simple.

An incorrectly sized generator can place undue strain on the unit, which could cause damage to connected devices. In order to correctly calculate your property’s power needs – and therefore buy the right generator – you have to consider a number of factors.

Follow these steps to choose the best generator for your needs:

1. Determine your running requirements

Generators are typically only used as the primary power source in rural areas and farms where there is no access to grid utilities. When they are used as a main power source, the generator should be sized for 70-80% capacity. This will improve performance and leave a margin for increasing power demand.

It’s best to only run a generator at full capacity for less than 30 minutes at a time.

2. Calculate your load size

Knowing what you need to power using a generator, will help you determine the correct size. It starts by creating a list of all the devices and appliances that need to be powered by the system. Add up the total wattage required by your equipment, and then calculate the maximum electrical input you will need the generator to provide.

In some cases, electrical equipment will have a different starting and running wattage. It is because these devices consume more energy to start up than it does to continue running. Be sure to factor the initial surge into your calculations.

Try our Power Requirement Calculator

3.  Do a conversion

You will now have the maximum required wattage for your new generator. After adding up your total power requirement in kilowatts (kW) you must convert it to kVA.

Generators are sized in kilo-volt-ampere (kVA), which is a measure of apparent power. It is important to always round up to the bigger size, as no electrical system ever offers 100% efficiency. As such, the kVA is known as the system’s apparent power.

If you know the efficiency of your system, you can convert from kVA and kW to reach a power factor between 0 and 1. Power factor helps you match your load size to the suitable generator. Generators are rated to have a 0.8 power factor by international standards. A 100kVA generator with a power force of 0.8 will not be able to power your household’s need of 100kW.

How to convert kVA to kW:

kVA x Power Factor* = kW

How to convert kW to kVA:

kW divided by power factor = kVA

Finally, you will have to analyse the feasibility of your power requirements, and your facility and the site location. In areas with limited space, it may be a problem to offload and deliver a large generator. The delivery vehicle will have to extend its stabiliser legs to offload, and there must be space to use a crane to position your generator unit.

Benefits of Choosing the Right Generator

While the process of choosing the right generator can be complex, there are many advantages to putting in the effort and enlisting advice from the professionals. Choosing the right generator will ensure:

  • Guaranteed performance
  • Increased lifespan of your system
  • No shut-downs due to capacity overload
  • No unexpected system failures
  • Smaller chance of damage to your assets
  • Assured personal safety

Speak to the Multilec team today if you need any assistance with sizing or choosing a generator or click here to request a free quote.