Choosing the right generator size is essential to ensure reliability, protect your equipment and avoid unnecessary costs. Whether your genset will be used for continuous, prime or standby power, careful planning can help you avoid common pitfalls.

Here are the key factors to consider:

1. Start with the Load

The first and most critical step in sizing a generator is understanding your power requirements. Identify the loads that are essential to your operation and determine their power demands when utility power is unavailable.

Create a list of all required loads, including their voltages, to size your generator correctly. Undersizing can lead to startup failures or even damage connected equipment. Conversely, oversizing can result in inefficient operation, increased maintenance and higher repair costs due to light loading.

As businesses grow, power demands often increase. It's common to oversize a genset by a margin to accommodate future expansion but avoid going too far — expansion plans that take too long to materialize can lead to unnecessary expenses.

2. Understand the Type of Load

Not all loads behave the same. Loads can be broadly divided into resistive and reactive (non-linear):

• Resistive loads (such as incandescent lighting or heating elements) draw the same current to start as they do to run.
• Reactive loads (such as motors, pumps and HVAC systems) require significantly more power to start, making them the biggest factor in generator sizing.

Motors and similar equipment often list their NEMA code on data plates, which indicates their locked rotor current. Using this data helps achieve more accurate generator sizing.

To manage reactive loads effectively and avoid oversizing, consider:

• Load sequencing: Bringing loads online in stages — allowing one motor to reach full operation before starting the next — can significantly reduce the generator's required capacity.
• Advanced starters: Using soft starters or Variable Frequency Drives (VFDs) can minimize the inrush current by controlling voltage and frequency during startup, allowing for a smaller genset without sacrificing performance.

3. Match Site Requirements

Voltage and frequency stability, as well as Total Harmonic Distortion (THD), must meet the needs of your specific application. Generators used for life safety, fire prevention or other critical systems have stricter regulations, often dictated by local, state and national codes. Always verify that the engine and generator are correctly sized to meet these performance standards.

4. Choose the Right Fuel

Fuel type is another important consideration for commercial and industrial generators. The three most common options are diesel, natural gas and propane, each with its own advantages:

• Diesel: On-site fuel storage, generally lower cost per kW (depending on emissions requirements), but higher fuel costs and emissions. Fuel must be delivered during extended outages.
• Natural Gas: Cleaner emissions, lower fuel costs and readily available if a gas line exists. Generators typically have a higher upfront cost, and new gas line installation may add expenses.
• Propane: On-site storage, relatively clean emissions and often lower fuel costs than diesel. Like diesel, fuel must be delivered during long outages and per kW costs tend to be higher.

Each site has unique needs, so weigh the pros and cons carefully before deciding.

Power with Confidence

The right generator sizing ensures optimal performance, protects your investment and supports future growth. For expert advice tailored to your specific application, reach out to your HIPOWER sales or support team.