Reefer containers are temperature controlled, which allows for easy transportation of temperature-sensitive cargo such as perishables and pharmaceuticals. When stored, reefer containers are typically plugged into an electrical socket, to ensure that the refrigeration unit is adequately powered. 

A genset (generator set) is an external generator that powers the refrigeration unit of a reefer container. Gensets are typically used in situations when reefer containers are stored or transported on a vessel, train or truck, and require an external power source. 

For example, when reefer containers are loaded onto a vessel or stored at a facility, they are typically plugged into a power network to keep the refrigeration unit working. 

However, this is not possible during certain types of transport (for example during container trucking or if reefers are transported on a train), in which case a genset is required. In this article, we will share more information on gensets, what types there are and when they are used, among other interesting information. Let’s jump right in!

How Gensets Work on Reefer Containers

Gensets power the refrigeration unit of a reefer container, to ensure that the inside of the container remains cool when in storage or during transit. To do so, they are powered through electricity and fuel. 

When a reefer container is stored at the port or a facility, gensets are typically powered by electricity. They are simply plugged in, and the genset draws power from the electrical grid.

However, when a reefer container is transported, the generator set is not able to draw power through an electrical socket. Therefore, it requires an external power source, which is fuel (typically gas, diesel, or petrol).

Types of Gensets Used in Shipping

Due to the different modes of transport that a reefer container is moved by, there are various types of gensets. Each of these gensets is used in specific applications, to ensure that the refrigeration unit receives enough power to cool the container’s interior. 

When it comes to shipping, generator sets are either integral, undermount, or clip-on. Let’s explore them in a little more detail, to understand why they are used in specific scenarios.  

Integral Genset

integral genset


  • Built into containers
  • Not commonly used for shipping
  • Used for long-term storage

Integral gensets are typically built into containers. These types of gensets are located towards the back of a reefer container, right above or underneath the refrigeration unit. 

The use of an integral reefer container usually means reduced capacity in terms of payload and cubage or a customized container that is modified to slightly longer specifications (to account for the internal generator set). 

An integral genset ensures an independent self-powered supply is always ready if the primary source of energy is not available. This solution ensures that the refrigeration unit is always on so that it can maintain the required temperature to preserve the integrity of the cargo. 

Integral generator sets are not often used in shipping as they either restrict internal volume or are longer in size, making them unviable for shipping on standard chassis or ocean vessels. 

Undermount Genset

underslung genset


  • Mounted underneath trailers
  • Commonly diesel-powered
  • Used when trucking containers

Undermount gensets, also commonly referred to as underslung gensets, are installed directly underneath a truck’s container chassis. These types of generator sets are mostly air-cooled and powered by diesel fuel.

When reefer containers are transported via a container truck from one location to another (for example from the shipper’s premises to the port), there is no electrical power grid to plug into. 

Therefore, specialized container chassis with undermount gensets are used, in order to continuously power the refrigeration unit of a reefer container. This ensures that the cargo inside these containers remains cooled during transport. 

Clip-On Genset

clip on genset


  • Installed onto reefers
  • Most commonly used genset
  • Easy clip-on mechanism

Clip-on gensets are installed directly on the reefer container by mounting them at the back where the refrigeration unit is located. These types of generator sets have a clip-on mechanism that allows for easy installation. 

Clip-on gensets are a good option if multiple reefer containers are transported via sea, road, or rail, where an electrical power grid or an undermount genset is not available. 

Certain warehouses or facilities are not set up with “reefer plugs”. Reefer containers need to be plugged into specialized power outlets that support 32 amperes and either 380 or 460 volts. In these types of scenarios, clip-on generator sets are ideal. 

When Are Gensets Used?

Gensets are used to ensure that the refrigeration unit of a reefer container is powered adequately so that the temperature can be regulated and the cargo is kept cool. Here are the most common scenarios when generator sets are used:

  • Reefer storage at warehouse or facility
  • Reefer transport (truck, rail, ocean)
  • Reefer storage when no electrical power is available 

How Much Fuel Do Gensets Consume?

Genset fuel consumption varies depending on the age and type of the model, mode of the setting, and what load they are under. On average a genset consumes between 2 to 4 liters of fuel per hour, in order to power the refrigeration unit of a reefer container. 

Below, you’ll find some of the main factors that determine the fuel consumption of a generator set:

  • Age – Generally speaking, older genset models consume more fuel, due to older parts and technology. Modern gensets are more fuel-efficient and also more environmentally friendly. 
  • Mode – Some generator sets have different modes. Some are equipped with an ‘economy’ mode, which is typically more fuel-efficient than gensets that are operating under the ‘normal’ mode. 
  • Type – As there are various types of models, some genset models are more powerful and therefore consume more fuel per hour. 
  • Load – Load is also an important factor when it comes to the power requirements of gensets. Generator sets that are under heavier load (when they require more power due to lower temperature settings) also burn more fuel. 

Popular Genset Brands

Generator sets are commonly used in shipping and there are a variety of different types and manufacturers. In the next section, we’ll be taking a look at some of the most common and popular genset brands on the market. 

We’ll be exploring their history, location, genset range, and what they’re most commonly known for. 


Almar was founded in 1988 by Alistair Forbes with its core business positioned in leasing and trading containers. They established their head office in South Africa and expanded operations in countries such as the United Arab Emirates, Brazil, India, Saudi Arabia, Kenya, Tanzania, and other countries in the African region. 

They are currently active in multiple industries such as logistics, cold storage, bulk liquid storage, transportation, remote side accommodation, and producing generator sets. 

Other product offerings include leasing and supplying all sizes of dry standard containers, reefer containers, and specialized shipping containers such as flat rack and open-top containers. 

With regards to reefer container gensets, Almar offers clip-on diesel-powered gensets that are designed to power refrigeration units of reefer containers. 


Carrier was founded in 1915 by Willis Carrier and is a publicly listed company on the New York Stock Exchange. As of 2020, they have 56,000 employees in different locations around the world with a revenue of 17.46 billion USD. 

The company is heavily involved in multiple industries that require refrigeration solutions in such as construction, consumer, cold chain, and transportation. Carrier also produces generator sets, data tools, and aftermarket parts. 

They offer diesel-powered gensets that are under their PowerLINE Series. These generators are designed for continuous and unattended operation during transportation via road or rail network. 

Thermo King 

Thermo King Corporation is an American company founded by Frederick McKinley Jones in 1938. It was later on acquired in 1997 by Trane Technologies. Thermo King provides products and solutions designed for road, rail, and sea freight. 

According to Thermo King, their SG generator sets are cost-effective, dependable, and have proven to be highly reliable. Generator options are available in both clip-on and undermount configurations. 

Their gensets have an output that ranges between 15kW to 22kW and are powerful enough for all types of reefers. Their gensets are also well known in the market and various types of shipping lines, such as Hapag-Lloyd use Thermo King generator sets.

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Andrew Lin

Co-Founder & Writer
at freightcourse

About the Author

Andrew is a multi-business owner with over 12 years of experience in the fields of logistics, trucking, manufacturing, operations, training, and education.

Being the co-founder of freightcourse has given him the ability to pursue his desire to educate others on manufacturing and supply chain topics.