A power outage can be a real hassle. Not only do you have to deal with the inconvenience, but you also have to worry about food spoilage, losing communication, and being in the dark. Power outages can happen for a number of reasons – from storms and natural disasters, to unexpected outages. A home backup generator provides peace of mind during this type of emergency. But exactly how long you can run a backup generator – to save the food in your fridge, stay connected to critical news, and not be left in the dark? Here are the answers to 17 common questions and how to find this information for yourself.

1. How long can you run a generator for?

When relying on a backup generator during a power outage or emergency, you need to know how long you can run it to keep the lights on and your food from going off. The answer depends on the type of backup generator and the fuel sources you use. Here is an overview.

You can run standby generators run for longer than portable generators due to their size.

A diesel portable generator can typically run for 8 to 12 hours on a full tank of fuel, at full load. Diesel standby generators used for home backup power supply can run for 24 hours.

A gasoline / petrol generator runs for a less time than diesel because they are less fuel efficient. At full load you can expect 5 to 6 hours of continuous running time before needing more fuel.

Natural gas generators (connected to a gas line) and solar generators have the longest continuous running time in the short term. This is because there is no tank to fill up.

For a propane gas generator, it depends on the size of the gas bottle or tank you use to fuel it. A 9kg gas bottle might run your generator for 3 hours at full load. An 18 kg gas bottle will run it for 7 hours at full load. Propane generators are not that common in Australia because of the amount of gas you need to run them.

You can run a solar generator continuously until the end of the battery life and many systems designed and installed to run this way in Australia. Whats more, solar generators require little to no maintenance by the home owner to run. As you will see as you read on, this is in stark contrast to the other backup generator types we examine here. It’s also a major benefit of investing in a solar generator with battery backup power.

Home fuel supply is a limiting factor for a backup generator’s runtime. If you want backup supply during power outages, make sure you have a spare fuel tank or two for your generator’s continuous use over a period of at least 3 days.

2. What factors determine a how long you can generator for?

What does continuous power mean?

A backup generator must be able to provide power of a set amount (e.g. full load, 50% load) for an unlimited number of hours per year under the agreed operating conditions. This is what is called the generator’s continuous power.

The continuous runtime of a backup generator is the length of time it can provide that rate of power.

What determines how long you can run a generator?

To answer this question, we need break it down. These are the factors that impact how long you can run a generator:

• the generator type – portable or standby
• the generator fuel type – petrol, diesel, gas, solar battery
• backup generator size – more powerful generators have larger tanks
• your running load (how much power you use or appliances plugged in)
• the generator’s engine design and ratings – in the manufacturers specifications
• your at home fuel storage.

First, let’s look at different generator types and fuel types.

3. Where do you find generator runtime information?

Generator runtime information is buried in the technical specifications or product brochure. If you wanted to know how long you can this 8kW Generac generator, you would look for ‘Rated Power’ (Generator size) and ‘Fuel consumption @ full load’.

Instead of rate of fuel consumption, some manufacturers will give you ‘Operating hours’. For example ‘11.5 hours @ full load’.

‘Full load’ is when the generator is being run at 100% of its rated output. So 8kW in this example. It’s unlikely you’ll run your generator at full load overnight remember. So ‘full load’ is a conservative estimate.

In this case we’re looking at a Generac gas generator. So you will need to convert gallons per hour into Litres per hour (1.42 gallons = 5.37 litres). Finally, you’ll need to convert litres into kg (LPG) to know how long your gas bottle will last. We take you through this example down below.

It might pay to look at how much noise the generator makes, if you’re in an urban area. Noise levels can determine whether you can run a generator overnight in built up areas.

Now that you know where to find the right information, let’s look at how long you can run different types of generators, and different fuel sources.

4. How long can standby generators last?

A standby generator is typically permanently installed with a transfer switch and intended to supply power during frequent extended power outages. Standby generators are generally larger for this reason. They’re often referred to as whole house generators.

Standby generators can run on diesel, gas, or solar and batteries.

The type of fuel is a big determinant of how long you can run a standby generator. If the standby generator has a fuel tank, you can run your generator as long as you have fuel in the tank to power it.

A standby generator run on natural gas (gas line) or solar power will have the longest continuous running time in the short term, because there is no tank to refill.

5. How long can you run a portable generator?

Portable generators have a fuel tank with a maximum fuel capacity. Most portable generators can run for 6 to 24 hours on a full tank, at full load. But it does depend on a range of factors including

• the generator fuel type (petrol, diesel, gas, solar)
• backup generator size (it’s rated output)
• the size of the fuel tank
• running load (how much power you use or the appliances plugged in).

These are the limiting factor that will determine how long your diesel generator run continuously. Let’s look at how this applies to a diesel generator.

6. How long can a diesel generator run continuously?

The backup generator fuel source we are looking at first is diesel. Diesel is pretty common in Australia for emergency backup power. We’re going to consider two generator sizes – 6kVa (portable) and 8kVa (standby or installed permanently). Both generators have fuel tanks.

6kVa diesel backup generator (portable)

As a guide, a 6kVa diesel generator (rated output of 6kVa) will use around 2.4 L of diesel per hour if run at full load. The same generator will use 1.8 L/hour at 3/4 load, 1.3L/hour at half load and 0.8 L/hour at 1/4 load.

So if that generator has a diesel tank size of 28L, it will run for just under 12 hours on a full tank. If you’re not running at full load, it will run longer (22 hours on half load).

8kVa diesel backup generator (standby)

An 8kVa backup generator in this example will use around 3.3 L/hour of diesel for the same size tank, giving a continuous run time of around 8 hours at full load.

7. How long can you run a generator on gasonline or petrol?

Petrol generators (also called a gasoline portable generator) can have a shorter runtime than diesel generators – around 6 to 8 hours on a full tank. This is because they’re generally smaller, with smaller tanks. They’re also not as fuel efficient.

How long you can run a diesel or petrol generator also depends on how much fuel you have in storage and how much of the generator’s rated output you use in your home.

8. How long can you run solar generators?

Solar generators with battery backup can provide a steady supply of power for as long as there is sunlight and as long as the battery has sufficient charge.

In the short term, the key to ensuring continuous runtime is the size of the solar system and the battery system.

The solar system needs to be large enough to run your home and to charge the battery during the daytime.

The battery needs to be large enough to power your appliances at night.

In the long term, how long you can run a solar battery system will depend on the lifespan of the battery.

With most homes now using lithium ion batteries, that lifespan is around 10 years. That’s if you charge and discharge the battery according to the manufacturers specifications.

9. How long can a natural gas generator run continuously?

There are two types of gas generators, each with a different answer to this question:

1. a natural gas generator (fuelled using a gas line into the property)
2. a bottle gas/ Liquid Propane (LP gas) / propane tank generator

Natural gas generators

A natural gas backup generator can run continuously over a period of weeks if the gas is piped into the generator. The main constraints on running this type of unit continuously are:

• the maximum annual runtime (see below)
• maintenance schedule and
• mechanical failure.

Natural gas generators are only used in parts of Australia where homes have piped gas from the street.

Propane generators

Propane generators (bottle gas) have more limitations. Let’s continue our Generac gas generator example from above. An 8kW propane generator or LP gas generator uses around 5.3 L (1.42 gallons) of propane gas per hour.

There are around 16 L of gas in a 9kg BBQ size gas bottle. You’ll need to swap this size LP gas bottle every 3 hours of runtime with propane generators. This is the continuous run time with a small gas bottle.

An 18kg gas bottle has around 35 L of gas so you can run your propane generator continuously for 7 hours before adding fuel.

That’s a lot of gas bottles in storage!

10. How do generator engine design and ratings affect runtime?

Generators need to meet certain performance standards or ratings in order to be sold on the Australian market. This means that manufacturers must test their generators in certain conditions and tell you how they generator should run.

Here are the design and performance rating that affect how long you can run your backup generator:

Maximum annual run time

Most manufacturers will indicate the maximum number of hours you can run a backup generator, per year. The generator’s performance can not be assured if run outside of these guidelines. A generator’s maximum annual run time is generally around 200 (9 days) to 500 hours (21 days).

If you need a generator for extended or frequent outages, make sure you find one with 500 hours or maximum annual run time.

Maintenance schedule

Most generators have a maintenance schedule that is important to the manufacturer honouring its warranty. With diesel and petrol generators, you may be able to only run your generator 50 to 100 hours between maintenance checks. Some checks need to be done with the engine stopped. Other checks will require a licensed professional to perform them.

A solar generator is the exception here, with fewer maintenance requirements.

Engine life

Diesel, petrol and gas generators have an engine life and batteries have a battery life. A generator’s engine life or battery life will determine how long you can run it over the long term (years).

A typical engine life for a diesel generator is around 3000 hours. For a battery, it depends on the chemistry of the battery cell. Lithium ion batteries last around 10 years. The way you run the generator can either shorten or optimise its engine life.

Conclusion

Recap: How long you can you run a generator for?

In the short term (over days), most portable generators with a fuel tank can run continuously for 6 hours to 24 hours. The range here is determined by generator size, fuel source and how hard you are running the generator. Standby generators can run for longer (24 hours) because they’re larger, but you need more fuel stored at home. Standby generators that run on natural gas or solar have the longest continuous running time as there is no fuel tank to refill. In the medium to long term (weeks and months), the backup generator’s engine design and ratings also determine how long you can safely run it to power your home.

You can read more about what generator you need to run a house here.

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