Diesel Generator FAQ: The Difference Between kVA and kW

We know the common scenario of a diesel generator shopper: You consult a power guide to determine how much power your home or office consumes, then you start browsing the selection of diesel generators to see which one best suits your needs. 

Suddenly, you see that the models are listing both kW and kVA as their power output and you no longer feel so sure about what you're looking for.

Don't worry, you're not alone. To put it simply, kW is the number you should really be concerned about. 

If you're intrigued about the differences, here's how it all works.

kVA: THE APPARENT POWER 

kVA is a unit used to measure the apparent power of a generator if it was 100% efficient. 

The problem is electrical systems are never 100% efficient, which means that you will never get the full kVA power potential. 

kW: THE REAL POWER

kW is the actual amount of power that is converted to real world output. 

This is why all electrical appliances are rated in watts (w) and kilowatts (kW), so you know exactly how much power is required to run them. 

SO HOW DO YOU DETERMINE THE DIFFERENT RATINGS? 

This is where it gets a little bit more complicated. 

You can convert kVA into kW, or kW into kVA if you know what the power factor of the machine is. 

Electrical efficiency is measured as a power factor between 1 and 0, with 1 being completely efficient, and 0 not having any efficiency. 

Generators have a power factor of 0.8, which means the kW or kVA ratings are determined through the following two calculations: 

CONVERTING kVA INTO kW 

Apparent Power (kVA) x Power Factor (pf) = Actual Power (kW) 

CONVERTING kW INTO kVA 

Actual Power (kW) / Power Factor (pf) = Apparent Power (kVA) 

A REAL WORLD EXAMPLE

So let's say you were looking at a diesel generator which was rated at 100kVA. 

To find the kW output of that model you would have to divide 100kVA by 0.8, which would leave you with 80kW. 

THE BEER ANALOGY 

Imagine you’re sat in your local pub with a pint in hand. The total contents of your pint glass (liquid & foam) is the kVA. However, only the liquid part of your beer serves to quench your thirst and this is the kW. 

The better the barman (or the more efficient the electrical system), the more beer (kW) you get! Simple, right? 

WHY IS kVA ADVERTISED BEFORE kW? 

In recent years, it has become standard in the power equipment industry to market diesel generators using the kVA rating front and centre. 

This is largely because bigger numbers look more impressive, but we always make sure to list the kW on our product pages so you know exactly how much power you are getting from your generator. 

STILL HAVE QUESTIONS? 

Hopefully, we've cleared up some of the confusion you may have been feeling about the kVA/kW terminology, but if you're still not 100% sure what you need to power your premises, get in touch with us. 

Our staff of diesel generator experts are always available for a chat and we'll be able to point you in the right direction. 

You can call us on 01437 700120, email us at info@thepowersite.co.uk or use the live chat in the bottom right hand corner.