What is a power generator, and how does it work?

Power generators are basically small power-plants. They allow their owners to generate electricity on-site, as a substitute or complement to electricity from the electric grid. Power generators and large thermal power-plants operate on the same principle: both burn fuel to create motion, or mechanical energy, and convert it into electrical energy. Generators have two main components: an internal combustion engine and an alternator. 

Just like the internal combustion engine of a car, a generator’s engine needs fuel to operate. Diesel, natural gas, propane, gasoline and biofuels are common options. The combustion of the fuel is used to create a rotational movement in a crankshaft in the following way: 

Air and fuel are mixed and ignite inside a cylinder. The combustion causes a small explosion that makes the piston in the cylinder rise and then fall. The piston is attached to a crankshaft, so as the piston moves it makes the crankshaft spin. Several pistons working one after the other create a smooth spinning motion in the crankshaft. In a car, this motion would be used to propel the car. In a generator, it is used for electricity generation

How does a generator produce electricity? 

The rotational motion produced by the engine extends into the second main component, the alternator. The alternator converts one form of energy, rotational kinetic energy into electricity by using the properties of electromagnetic induction, the physical phenomenon by which variable magnetic fields create electrical currents. The alternator has two parts—a stator and a rotor. The stator is a housing made up of many copper windings, and as the rotor spins inside the stator, its magnetic field rotates as well. The rotating magnetic field causes the electrons to flow in the stator, and thus a current of electricity is produced.  

Components of a power generator

As well as the generator and alternator, a power generator contains other components to ensure its correct operation. A fuel system ensures that the generator’s engine receives a steady supply of fuel. In smaller generators, the fuel system can be as simple as a fuel tank and a fuel filter. The generator also needs to supply electricity at the correct voltage, so a voltage regulator is included to ensure the right voltage is achieved and maintained. Parts of the generator get hot during operation, so to prevent overheating, a cooling system is needed. Smaller generators tend to be air-cooled; larger generators need to be water-cooled. Then there is the exhaust system, which removes hot combustion gases. Catalytic converters, dust filters or scrubbers can be added to clean up the exhaust. In larger generators used in cogeneration applications, the exhaust gases can be used to heat water, for example, as part of a district heating scheme. This means that the fuel energy is converted to both electrical and useful heat energy, optimizing the efficiency of the machine. 

In addition, there is usually an oil system for lubrication, a battery for ignition, a charging mechanism for the battery, a control panel for monitoring the different gauges and parameters of the machine, and the frame in which all the machine’s components are housed. 


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Diesel vs. propane vs. natural gas generators 

Generators can run on a variety of different fuels, from heavy fuel oil to propane gas. The decision over which fuel to use depends on various factors: the cost of the generator, the price of the fuel, the availability of the fuel, fuel storage considerations, each fuel’s emissions profile, and noise constraints. Generators can be designed to work with a wide range of fuels, from naphtha to biofuels, but some of the most commonly used fuels are diesel, propane and natural gas. 

What are diesel generators and how do diesel generators work? 

Just like car engines, generator engines are different according to which fuels they use. Diesel engines are a type of compression-ignition engine. Such engines ignite the fuel by heating it above a its autoignition temperature. Diesel fuel’s relatively low autoignition temperature of 410°F makes diesel fuel idea for, well, diesel engines. Typically, to start smaller diesel engines, an electric starter motor pushes the engine’s pistons, compressing the air located inside the engine’s cylinders and increasing its temperature. This is known as cranking the engine. When the temperature inside a cylinder reaches the fuel’s autoignition temperature, fuel is injected into the cylinder, and immediately ignites. This pushes the piston back (with an exhaust valve opening to expel the gas), and moves the crankshaft. The other cylinders fire as well, resulting in the turning motion needed to generate electricity and sustain the compression-ignition cycle of the engine. 

In contrast, gasoline engines inject air and fuel into their cylinders at the same time, and require a spark for ignition. Because they have a simple ignition mechanism, diesel engines tend to be very reliable and last a long time. The absence of spark plugs also eliminates the emission of radio frequencies that could interfere with sensitive electronic equipment. Diesel engines are also highly efficient, including at lower loads, thanks to their high compression ratio.  

Did you know that only vehicles with diesel engines are allowed in the United States National Radio Quiet Zone? The United States National Radio Quiet Zone is a large zone in Virginia and West Virginia where radio emissions are restricted in order to avoid interference with the radio telescopes present in the area. (Cell phones, Wi-Fi and microwave ovens are also banned.)

What are propane generators and how do they work? 

Propane is another great choice to fuel a generator. Propane engines are very much like gasoline engines in that both operate on the spark-ignition principle. Propane engines injecting a blend of air and fuel into the engine’s cylinders, where a spark plug ignites the mixture.  

Propane presents several advantages that make propane generators particularly well suited for residential backup power applications. Gasoline and diesel can both go bad after a few years and keeping a canister of either fuel in the house could produce fumes. Gasoline and diesel can also be spilt, which would result in a difficult cleanup. In contrast, propane can be kept indefinitely, with no risk of spillage. Crucially, many homeowners already have a propane cylinder on hand, eliminating the need to keep an additional fuel canister in the house. 

What are natural gas generators and how do they work? 

Natural gas generators are very similar to propane generators. Both require spark plugs and both have clean emissions profiles. Using natural gas is usually only practical in locations that are served by a natural gas distribution network, self-storage being rarely an option. This is not always the case in rural areas.  

Natural gas generators are well-suited for commercial and industrial applications where there is a reliable supply of natural gas. In the United States, natural gas tends to be very affordable and widely available. In large-scale applications where large quantities of fuel are used, not having to store fuel on-site is a major advantage. In addition, because natural gas burns very cleanly, the environmental regulations for natural gas generators tend to be significantly less restrictive that those that apply to liquid fuel generators, and as a result, they can sometimes be used in a more flexible way than diesel or gasoline generators. 


What are dual-fuel and bi-fuel generators? 

Dual-fuel generators are generators that burn two fuels at the same time. Some dual-fuel engines, for example, inject propane and diesel into the cylinders at different times in the compression stroke. The diesel fuel auto-ignites by compression, as in a diesel engine, causing the propane to burn as well. This results in an engine that presents the advantages of both diesel and propane engines in the same machine.  

Bi-fuel engines can burn two fuels, but only operate with one fuel at a time. They provide their owners with fuel flexibility. For home generators, for example, this ensures that if propane runs out, the generator can continue to run on gasoline. In industrial applications, the bi-fuel feature allows owners to optimize their operating costs by choosing the fuel that is the most convenient or cheapest to use at any given time. In oil and gas extraction applications, for example, having the option to run a generator on natural gas when it is being produced is a great way to save on costs. In utility power generation application, running a generator on natural gas rather than diesel during ozone season limits nitrogen oxide emissions, which contribute to the formation of ozone. 

Standby vs. prime vs, continuous power generators 

One of the biggest criteria in choosing a generator depends on what you want to use it for. Generators are rated differently for specific uses and for performing in different conditions. Getting the right generator for the job is like getting the right batteries in an RV: one battery starts the RV engine so it needs to give a powerful burst of electricity, whereas the leisure battery running the lights and fridge needs to release a slow amount of electricity over a longer time. 

Generators can be thought of in the same way – will the need for power be very high for a short amount of time or fairly high for longer period, or will the generator be in continuous usage? These are three main categories of generator use: standby, prime power and continuous power. 

Many generators are now produced in a modular way, offering the possibility to have best combination of engine and alternator to match the application.  

An individual generator may be used for different applications, and present different nameplate output ratings depending on the application. In other words, the same generator could provide 100% of its maximum rated power in one application such as emergency use, but only 70% in continuous operation. 

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What is a standby generator, and how does it work?  

A standby generator is designed to take over supplying electricity to a site in case of power failure, for as long as it takes until power is restored. Hospitals, datacenters, government buildings, offices and many other buildings need standby generators to ensure that in such an event, critical services are maintained. Beyond that, non-critical services such as hotel lighting and air conditioning also need to be maintained in the case of a power outage. Standby generators need to be up and running in seconds to minutes, depending on the criticality of the application. They are designed for limited use and are intended for speedy, powerful starts. 

What is a prime power generator, and how does it work? 

Prime power generators are designed for variable load and unlimited use. They are used in situations where electricity is needed, but in fluctuating amounts. An example would be for activities at the extremities of a site where there is no power, e.g., to power a dockside gantry crane working in a port, or to provide extra power to a building during peak times. For commercial and industrial users, using prime power generators during periods of peak demand can be an effective way to reduce or eliminate demand charges from the utility. In some cases, prime power generators can allow such users to grow their activity while avoiding a costly upgrade to their grid connection infrastructure. Prime power machines are not designed to be run 24/7 at full pelt, but to respond to flexible demand at different times of the day. 

What is a continuous power generator, and how does it work? 

Continuous generators are workhorses designed to provide a permanent supply of electricity. Continuous generators are necessary in places where there is no reliable power grid, such as remote mining operations or onboard ships.  

There are design differences between generators made for different uses. For example, prime power and continuous power generators feature larger cooling systems, and tend to operate at lower revolution speeds to prolong their life, whereas standby generators need quicker speeds to power up quickly.  

Home vs. commercial vs. industrial generators 

How does a home generator work? 

Home generators are smaller than the generators used in commercial and industrial applications, but work in the same way, and have the same components. The best way to install a home generator is to connect it to the home’s main electrical panel, so it can power all of the home’s electrical circuits when needed. This is done with a device known as a transfer switch. The transfer switch prevents electricity from travelling from the generator and into the power lines, so utility workers don’t risk getting an electric shock from someone’s home generator when they are working on the lines.  

Most homes use generators as standby power. In case of an electrical outage, the generator senses the loss of power and automatically kicks in, usually within seconds.  

Portable generators are scaled down versions of home generators and feature an engine roughly half the size of a lawnmower engine. Many portable generators weighing 50 pounds or less are available. Their portability makes them well suited for camping trips, cookouts, and construction projects.  

Modern portable generators come with standard AC outlets and USB charging ports. Some even have Bluetooth connectivity and an app that allows the user to monitor the status of the generator on a smartphone. Others have built-in batteries which provide power for some time without having to start up the engine. Portable generators must never be used indoors, inside a vehicle or inside a tent because they can release deadly carbon monoxide gas. 

What size home generator do I need? 

Even a small generator is usually enough to power all the lights, electronic devices and small appliances present in the home. To continue using power-hungry appliances such as electric ranges or electric baseboards, a larger generator may be needed. The size of a home generator depends on how much electricity you use. You can use our generator size calculator to consider your needs.


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How do commercial generators work? 

Commercial generators work as described above and can be run using different fuels. Common commercial applications are to provide standby power in the healthcare and datacenter sectors. Hospitals require reliable back-up power generation as any loss of power could mean loss of human life, as life support systems and operating theatres need continuous power. Datacenters also need a reliable power supply as a power outage could endanger important government and business data. There are many other commercial sectors that choose to install generators as standby power, from hotels to schools to commercial office blocks.  

Generators are also used to supply continuous power in commercial and institutional settings, for example in combined heat and power schemes—for cogeneration. Where a large building or campus needs heat as well as electricity, it makes sense to use a generator. This is because when fuel energy is converted to electricity in a generator, or, indeed, in a power station, around half of it is lost as heat. Instead of wasting that heat, cogeneration schemes use it to keep the building warm, alongside producing electricity. 

What size commercial generator do I need? 

The size of the generator depends on the application, and ensuring that the rated power matches the use for standby, prime power or continuous power applications. You can use our industry leading solution, PowerSuite, to understand your power generation needs.  

How do industrial generators work? 

Industrial generators work in the same way as described above but are usually designed to be more robust so that they can operate in rough environments. Generators used in mining applications, for example, may be exposed to very dusty conditions, and thus require enhanced air and fuel filtering components. Generators used at chemical and petrochemical facilities may operate in corrosive or explosive environments and so require the appropriate safety features. Additionally, industrial generators may have enhanced reliability requirements. Oil and gas drilling operations, for example, can generate tens if not hundreds of thousands of dollars of losses in a single day if on-site power is unavailable. In mining operations, a loss of power can mean a loss of ventilation in the mine, which would put the lives of underground workers at risk. Industrial generators have to be configured to provide the mix of power needed—standby, prime power and continuous power—to ensure safe and efficient operations. There is a world of difference between a generator keeping the lights on in a Midwest office block and one heating a building in the frozen wastes of Canada. 

Electrical utilities can also use generators to power the electrical grid. Because of their great flexibility and fast-start capabilities, generators are the ideal complement to solar and wind power generation resources on an electrical grid. For example, when clouds appear and obscure the sun, generators can quickly kick in and pick up the load previously served by solar panels. Generators are also ideal for powering the electrical grid on islands, where they, increasingly, work alongside with solar, wind and energy storage resources.

Sometimes the distinction between commercial, industrial and utility use becomes blurred. Some military bases, for example, have generators that ensure power is available if there is a loss of outside electrical service, but also export power to the grid in normal times, effectively serving as power plants for the utility. In the same way, some datacenters use their standby generators as mini-power plants to serve their local grid when they are not needed by the data center. 

What size industrial generator do I need? 

It’s ‘horses for courses’. The right size is dependent on the type of application as well as the electricity needed. You can use our industry leading solution, PowerSuite, to understand your power generation needs.

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