Correctly sizing a generator is crucial to ensure that the system operates efficiently and without interruptions. This process goes beyond simply adding up the consumption of the connected equipment; it is necessary to consider key factors such as starting peaks, load type, simultaneity factor, and the operational conditions under which the generator will be used.
We will explore these aspects in detail so that you can make an accurate estimate. In any case, it is essential to pass the installation details on to professionals who will ultimately study the project and propose the correct solution.
Identifying the type of load you will supply
One of the first steps is to determine the type of load the generator will supply. Generally, it is classified into two main types:
Difference between resistive and inductive loads
- Resistive loads: These are loads that convert electrical energy into heat, such as incandescent light bulbs, electric stoves, and heaters. These loads have a linear behaviour, meaning they do not require additional power once connected.
- Inductive loads: These involve equipment containing coils, such as motors, transformers, and compressors. These loads have a low power factor, meaning they require more current to operate, especially during startup, when energy demands can multiply. This phenomenon is known as the start-up peak or starting surge.
Starting peaks: how they affect the generator’s capacity
Starting peaks are temporary power increases that occur when certain equipment, such as motors or compressors, are started. These peaks can be 2 to 7 times higher than the equipment’s nominal power. If this factor is not considered, there is a risk that the generator will be unable to supply the required power during critical moments.
- Calculating the starting peak: To calculate the starting peak of an electric motor, for example, you need to multiply the nominal current of the equipment by a factor that depends on its size and type.
Determining the entry sequence of these loads
An aspect that often goes unnoticed is how these loads will demand energy. Will all systems start up simultaneously? Will they enter progressively? It is important to answer these questions to determine the entry sequence of all these loads. Together with their type, this will be essential in sizing the equipment.
Calculating the total consumption of the equipment
Once the type of load has been identified, the starting peaks have been considered, and the entry sequence is known, we can calculate the total consumption required by the installation. To do this, it is essential to know the power in watts or kilowatts of each piece of equipment and sum them. However, it is important to consider that not all equipment will operate simultaneously, which leads us to the next point.
Simultaneity factor: optimising the generator’s capacity
The simultaneity factor is a coefficient that indicates the fraction of the total load that will be operating simultaneously at any given time. By applying this factor, we can reduce the estimated total power, as not all equipment will be operating at full load simultaneously.
How to calculate the simultaneity factor: This value is obtained based on specific knowledge of the installation and the behaviour of the equipment. In a residential installation, for example, the simultaneity factor is usually between 0.6 and 0.8, while in industrial installations it can be lower, around 0.5. However, these are estimated ranges. It is essential to conduct a detailed study of the installation to determine this factor.
Including a safety margin in the estimated power
In addition to considering the starting peaks and simultaneity factor, it is advisable to include a safety margin over the estimated power. This margin covers unforeseen events such as the installation of new equipment in the future or occasional increases in demand. In any case, this safety margin should never lead to unjustified oversizing of the generator, as such oversizing not only results in higher investment but also affects the generator’s operation.
Why is a safety margin necessary?
The safety margin not only prevents overloads but also ensures more efficient operation of the generator. When a generator operates close to its maximum limit, it tends to heat up more, which can reduce its lifespan and increase the likelihood of failures. However, as mentioned earlier, excessive oversizing can cause the generator to run at low load, which also harms the engine and its lifespan.
Differentiating between continuous power and emergency power
It is essential to distinguish between two types of power provided by a generator:
- Continuous power: This refers to the amount of energy the generator can supply continuously over an extended period. This is the capacity at which the generator should operate in applications where it is the primary source of power.
- Emergency power: This refers to the amount of energy the generator can supply in the event of a power failure, but only for short periods. It is ideal for situations where the generator operates intermittently.
When do you need continuous power and when do you need emergency power?
If the generator will be the primary power source, for example, in remote locations without access to the electrical grid, you will need to consider the generator’s continuous power. If the generator will be used for emergency situations, it should be sized based on emergency power.
How to calculate each type of power according to your needs
- Continuous power: Calculate the average demand of the connected equipment and adjust the generator’s capacity to meet that energy demand over time.
- Emergency power: Consider the maximum peak demand during the highest consumption period and select a generator that can supply that power for short periods.
Other factors to consider when sizing a generator
In addition to the above, other factors influence the correct selection of a generator:
- Altitude, temperature, and humidity: Generators may experience power losses when installed at high altitudes or in environments with high temperatures or humidity. This is known as derating. Therefore, if the generator will operate under any of these conditions, we need to quantify the power losses of the engine and adjust accordingly.
