When the lights go out, and you find yourself in need of power during a storm or other emergency, you become suddenly aware of how dependent we all are on the electrical grid, and how vulnerable we are when the system fails. Even if it is just for a few hours, you'll immediately realise that without electricity you have no lights, heating systems, power showers, electric cookers, toaster, microwaves, hair dryers, air conditioners, fans, washing machines, irons, hi-fis, Amazon Alexa, smart appliances, internet or TV.

This short-term challenge can be addressed with an emergency back-up generator or household battery system (such as the Tesla PowerWall) to keep your home running smoothly.   When considering other scenarios, such as longer term power failure or situations in which power cannot be restored for a significant length of time, a battery system has its limitations, and only a household generator will supply you with ongoing electricity in the long-term.

The right emergency backup generator can provide enough electricity to ensure you are able to operate ongoing as a household regardless of the grid, and with limited maintenance. However, it doesn’t come free - check out the details below to help choose the right one for your needs.

What to Look for in a Petrol or Diesel Emergency Backup Generator?

Engine Type

The type of engine used in your generator can have a dramatic effect on how long it lasts, the availability, installation costs and the cost of its fuel, the noise it generates and its maintenance requirements.  For this article we are only focusing on petrol and diesel generators, but other types exist including hydrogen generators, solar and liquid propane.

• The generator is typically less expensive than a diesel equivalent
• Petrol is cheaper per litre
• Petrol generators run more quietly than diesel
• They produce less harmful carbon dioxide fumes
• They require routine maintenance such as oil changes, spark plug replacements and carburettor cleaning
• Petrol lacks stability and as a consequence the temperature of the system can escalate, reducing the lifespan of the component parts.

• Better for rare or occasional, non-intensive use

Diesel Generators

• Higher fuel efficiency than petrol – use up to 50% less fuel per hour
• Lower maintenance requirements
• Longer lifespan

• Better for more regular, intensive use

The engine type and size are the most significant influences on key issues that you'll want to consider - the noise that it generates, and its portability, so be aware that there can be a bit of a trade-off at play when wanting to maximise your electricity generation to keep your household running as normal.  Also note that generators are usually extremely heavy and cumbersome, and larger systems are only suitable for solid footings, or in an exterior building.

Location - Small generators can easily be located to wherever they are needed and don't require a permanent site. As standard a household generator is usually extremely heavy and cumbersome, and weight significantly more than an everyday household appliance such as a washing machine. All petrol and diesel generators should be located outside due to the toxic fumes they emit – they should be sited a minimum of 50cm from the exterior of your house, and at least 150cm from any door or window.  Whilst a generator can be stored in a garage or shed whilst not in use, it is best to have an external generator enclosure so that the generator can be used safely outdoors regardless of the weather.

Fuel availability in a crisis - whilst all fuel types are currently available, will these still be available and affordable in a crisis?  Petrol and diesel can be accessed at petrol stations across the country, but we have all witnessed the queues and supply issues that arise extremely quickly, sometimes based on just rumours of availability restrictions. 

Fuel storage - In order to ensure your household is able to use the backup generator, without fuel availability concerns, ensuring you have adequate fuel storage is a logical next step.  There are rules on how residential properties can store different fuels, and these need to be understood and followed in order to comply with the law and health and safety.   In the UK there is no limit on diesel storage, however the legal limit on petrol storage at home is 30 litres.  This can be increased to 275 litres if you notify your local Petroleum Enforcement Authority.  Fuel in the tank of your car is excluded from this limit.

Petrol and diesel should be stored in either suitable plastic or metal containers, demountable fuel tanks, or a combination of the two.  5L plastic jerry cans or 10L metal jerry cans are classed as suitable containers, but these need to be labelled up as ‘Highly Flammable’.  The maximum amount of fuel you can have in one container is 10L.  Fuel cannot be stored in living areas and should be securely kept either in a shed or garage, away from any source of ignition.

Fuel expiry – once a container has been filled with fuel the quality begins to deteriorate. Petrol can be kept for up to 6 months, whilst diesel can be stored for up to 12 months before it starts to become a little gummy.

Notifying your local PEO – In order to store more than 30L of petrol at your home you are legal required to notify you local Petroleum Enforcement Authority in writing, providing them your name and address of the storage location.  Further information and  storage requirements can be found on the government website here.

Noise - for short-term usage this might not be a particular concern, but for longer-term use, you may want to consider a silent generator, especially if your generator is located very close by.

Portability - are you sure that you'll stay at your property - might you benefit from being able to conveniently transport your generator with you?  Depending on the size and type of generator, this will either meet the criteria as portable, semi-portable/towable, or fixed/static.  As with all of these factors, there is a balancing act that occurs in making the right selection.

Household battery systems - having a generator that can just be switched-on if the power cuts out is useful, however having a generator that is integrated with a household battery system, such as Tesla's PowerWall, will improve your set-up vastly.  This system will not only provide you with immediate back-up power without the generator switching on, but also enabling you to store energy generated and potentially integrating with other systems you might have such as solar panels.

Installation / Household integration – whilst you could have a back-up generator stored and ready for use in a disaster, if it isn’t properly installed then you are going to have limited functionality, perhaps only running a couple of specific appliances such as a freezer for frozen food supplies.  We recommend you have a professional installation (which is likely to cost up to £1000) which will cover electrical work, inverters, testing and other technical installation requirements. Note that a concrete pad is required for a household generator, and if you don’t already have this in place it is likely to cost around £500.

Power generation

Any generator will work, but if you have a large enough one, it can provide power for your household to continue as normal for days. However, these are usually very expensive and often the best emergency backup generator to select is one large enough to provide power for a house but only with the household making intelligent decisions about how to minimise the power they are using. 

Note that a large generator will require considerably quantities of fuel - so this will need to be on hand and safely stored, complying with legal restrictions.

Emergency backup generators have a wide range of power outputs available, with typical values ranging from 3 - 25kW, with 5kW being the minimum to keep essential household appliances and systems operating.

The below list provides the running wattage for a variety of household appliances and equipment.  Note that the ‘starting watts’ should be added to the ‘running watts’ in order to understand whether you would be able to function that appliance with a specific generator.

Maintenance requirements

All generators require maintenance, though the frequency and type of work depend on the type of engine used. Petrol engines require routine maintenance such as oil changes, spark plug replacements and carburetor cleaning. Diesel engines may be easier to maintain, depending on your maintenance schedule.

It is recommended that your generator is serviced at least once a year.  To find a local firm who will provide a competitively priced service, we recommend you Google “home generator service near me” or similar.

Wrapping up

These are the key factors to consider when choosing the best emergency backup generator. Emergency backup generators are available in a variety of sizes, types and power outputs. Depending on your needs, you may be able to use a small petrol generator for a few days to keep your key appliances functioning, or a large diesel-powered generator could keep your entire household running unaffected.

Author's Note

Whilst we're not recommending any specific products, we recently invested in a Hyundai 5.2kW Diesel Generator (silenced). 

This weighs just over 150kg, is approximately the size of a domestic washing machine, has a 13L diesel tank providing up to 16 hours of run time.  It’s on wheels meaning it is portable, although not easy to transport.  Does this meet all of our needs? Not quite - at 5.2kW we would have preferred a generator with probably close to double the wattage to meet our household needs. However it does have an Automatic Transfer Switch that will sense a power cut and automatically start the generator even we're not around. The cost was a crucial element to us, and at approximately £1,800 we felt this met the minimal requirements – we will be able to power our fridge/freezer, oven, TV, lighting, laptops, radios and a variety of lower wattage appliances regardless of electricity supply from the grid – note that we chose a diesel generator because unlike petrol, there is no legal limit on diesel storage, and as such our current 50 litres will keep the generator running continuously for over 2 days.  If we believe that external risks are increasing, then we will increase our fuel storage accordingly.