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How efficient is a diesel generator?

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One of the biggest advantages of choosing a diesel generator over a petrol or natural gas generator is the efficiency of a diesel engine. In short, you will be able to run a diesel generator at the same power output for longer, while burning less fuel.

Although diesel fuel costs more than petrol in the UK, the engine efficiency of diesel generators means they use less fuel to generate power. This means although the initial cost of a diesel generator may be higher, you’ll be saving on fuel costs in the long run.

Throughout this article we look at the overall fuel efficiency of diesel generators, how they work, what makes them so efficient, and the advantages there are to choosing diesel engines over a petrol or gas engine.

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How do diesel generators work?

Diesel generators, also known as electric gensets, have been around for more than a century. They work slightly differently to other engine fuel types because they have an internal combustion diesel engine.

The diesel engine design uses unit injectors to introduce compressed air (carbon dioxide) and diesel fuel into a combustion chamber.

This process generates heat to ignite the fuel, the higher the compression ratio the less diesel is needed and so can burn fuel at a slower rate making it more fuel efficient.

This process starts the generator, where the internal combustion engine turns the chemical energy contained in diesel into mechanical energy, which then gets converted into electrical power.

Because of diesel generator efficiency, it makes this type of generator a popular choice where it’s needed for prime power or to operate continuously.

Often in locations where it’s not possible to connect to grid power or a natural gas source, such as construction sites or events. 

Why is diesel used in generators?

For starters, diesel is widely available, it runs cleaner and lasts longer than petrol. If you’re relying on your generator for backup power generation, it’s worth storing fuel to make sure you have a reliant fuel source when it’s needed.

The benefit of diesel is it can be stored for longer periods of time than petrol, and it’s also less flammable so storage is safer.

Diesel also has a higher energy density than petrol. This high energy density gives you more energy in a litre of diesel than you would get in petrol. This means diesel engines in generators can produce more electricity to suit greater power needs. 

How much power can a diesel generator produce?

The power factor behind diesel generators depends on a few things. Industrial diesel engines will, of course, generate more power than smaller and lighter generators.

If you are using a generator to power a home, you’ll probably have a generator that produces 8 KW to 30 KW of power, whereas, a larger generator used for commercial use can range from 8 KW to 2,000 KW. 

Diesel generators run better when they are loaded, so it’s recommended that you always keep your generator at 50% of the maximum load or higher. This will also help to ensure the generator efficiency is at its best. 

How long can a diesel engine last?

A diesel engine can last a long time if you take care of it. With proper maintenance it can last up to 20 years or more.

Because diesel generators don’t use a spark ignition source, they don’t rely on other components such as spark plugs that require regular maintenance, therefore less maintenance is required for a diesel generator.

However, the heavy components in diesel units still require occasional maintenance, even if it’s just a light oil from time to time to ensure the engine’s performance is still at its best. This will help ensure its long life. 

Can you put normal diesel in a generator?

Diesel generators will work with normal diesel, known as white diesel, which you can buy from a petrol station. It’s easily available and perfectly acceptable to use in your generator. It’s also safer to store, as it’s less flammable than petrol. 

Previously, red diesel may have been an option for you if you were entitled to use it, but due to new rules and regulations that came in from April 2022, red diesel has even tighter restrictions on which industries can use it. 

See our related article for more information, How will the changes on diesel tax affect my business?.

What are the advantages of diesel?

There are several advantages to diesel generators, one of the biggest being their fuel efficiency and their ability to create greater power generation.

Although the diesel engine has been around for well over 100 years, it’s still one of the most efficient engines on the market.

In a generator it makes for an efficient way to supply power when you need it.

Advantages of diesel engines include:

  • Better fuel consumption
  • Lower maintenance costs
  • Produce more power
  • They are safer to store
  • Generally have a longer lifespan

Although there are some disadvantages to diesel generators, such as noise and initial costs, they are often preferable to other generators, such as natural gas generators, for several reasons.

Mainly for their sturdiness and reliability, which is particularly important when it comes to emergency power needs.

The gas industry can be disrupted, so the supply of natural gas may falter and natural gas generators also don’t perform as well when it comes to generator efficiency – making diesel a preferred choice over natural gas generators. 


With the ever-changing supply and pricing changes in the oil and gas industry, it can be reassuring to know the generator you own is going to run efficiently.

Diesel generators are some of the most efficient generators on the market. Of course, the needs you have for a generator will determine which generator is going to be best for you. 

If you would like to know more about buying a generator, and which type will be the best solution for your power needs, our team here at Solent Power would be happy to help. Contact us today!

Paul Phelps Solar Power Owner
Paul Phelps
Paul is the MD of Solent Power and specialises in emergency power solutions, helping to protect your facilities from power loss. Get in touch with us today to discuss the different power brands that we can offer and how they can suit your needs.
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