Anyone in the UK planning an off-grid solar power system has to take into account the many days we don’t have sunshine. Full energy independence means having the ability to generate energy regardless of the conditions, which is where a generator comes in.

There are a few options when selecting a generator backup for an off-grid solar system and that’s what we are going to discuss today.

Do you Need a Generator Backup for Your Solar System?

A generator is your backup plan for those days when there isn’t enough natural light around to generate enough solar energy for your needs.

Not every solar power system will need a generator. They are mainly for situations where energy is required regardless of the conditions. If you’re living or working in the property and absolutely must have power, a generator is a viable backup solution to keep batteries charged.

You could use a wind turbine as a secondary power source but in situations where that isn’t practical or possible, a generator is the next best option.

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Types of Generators for Off-grid Solar Systems

There are two main types of generator, conventional generators and inverter generators.

Conventional generators are those used in workshops, on boats and anywhere that portable energy is required. They are relatively cheap, readily available and easy to maintain. The downside is that they supply ‘dirty’ or fluctuating energy and can be noisy.

Inverter generators are more advanced generators that deliver refined energy better suited to home appliances and electronics. They are also quieter and very fuel efficient. The downside is that they are substantially more expensive than a conventional generator and have shorter run times due to smaller fuel tanks.

Backup Generator Fuel Types

Typically, generators run on diesel, petrol, propane or natural gas. You can also get hybrid generators that aren’t selective about the fuel they use.

Diesel is easy to access, not very flammable and offers high efficiency. Diesel does have a limited shelf life and the generator requires heavy loads to work best.

Petrol is also easy to access but more flammable than diesel. It also has a limited shelf life and requires careful storage.

Propane is cleaner and quieter than diesel or petrol but harder to get. It can also be more expensive to buy and burns faster so isn’t as efficient as petrol and diesel.

Natural gas is also cleaner and quieter than diesel or petrol and performs well when it’s cold. Natural gas generators have a higher fuel consumption and are more expensive to buy.

You can also buy hybrid or dual fuel generators that use a combination of fuel types. The same characteristics still apply to each fuel type though.

Automatic or Manual Generators

Another consideration when planning generator backup for a solar power system is the support mode. Do you want an automatic system or a manual one?

Automatic generators are wired into your solar power system and will be triggered when battery levels are low or when the draw on the system is high. Automatic systems can be used either to charge the batteries or to supplement the power available in high use situations.

Manual generators will need to be started by hand when required.

As you might expect, automatic generators cost more than manual generators due to the extra electronics required to link it to your solar power system. They do offer advantages in certain situations though.

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What Size Generator do You Need for Your Off-grid Solar System?

Generators are sized by their wattage capacity and how much energy they can deliver. To calculate the size of generator, you need to know the power requirements of your solar power system.

Use this calculator to do that.

A typical backup generator for an off-grid solar system would ideally produce twice the wattage your inverter would. For example, if you’re using a Victron Phoenix 24v inverter that can handle a continuous 650w, you would want a 1300w generator.

Selecting a generator to support an off-grid solar system is one of the many decisions you’ll need to make while designing your setup. We have covered many of the basics here but are always available if you have specific questions or concerns about any aspect of off-grid solar systems.

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