What generator power do I need? (kW/kVA + practical examples)

What generator power do I need? A simple guide (with examples for Portugal)

The most common question before buying is: "What generator power do I need?" . And that makes perfect sense — because the right generator isn't the "strongest," it's the one that can handle your actual power consumption , including peak starting loads .

1) Mistake #1: Forgetting about starting peaks (engines)

Motors and transformers can require very high peak currents when starting up. Atlas Copco explains that starting currents associated with motors/transformers are one of the most important points in sizing, and cites that they can be several times the current under load.

What this means at home:

  • Refrigerators, water pumps, and some appliances with motors require a headroom to start without "flooding" the generator.

2) Practical 4-step method (the most "foolproof")

Step A — List what you want to connect “at the same time”

For example: refrigerator + router + lights + chargers + TV.

Step B — Add the operating power (W)

Use the equipment label (W) or manual.

Step C — Identify the largest “engine” (peak)

Refrigerator? Pump? Compressor?

Step D — Add margin

GRUPEL (the manufacturer) cites a practical approach: to handle starting peaks (pumps/motors), "normally 25% is added," and also warns against oversizing to the point of systematically operating with very low load.

Furthermore, GRUPEL warns that operating a generator below approximately 30% load can cause engine problems.

Summary:
✅ Margin helps with peaks
✅ But a "giant that's always empty" isn't ideal either.

3) kW vs kVA (no confusion)

  • kW → useful power (what “does work”)

  • kVA → apparent power (in practice, many generator plugs come in kVA)

If the advertisement only gives kVA, check if it also indicates kW or the power factor . To compare different models, always try to compare the same unit.

4) Sizing examples (guidelines)

These examples are meant to guide your choice and research (“buy generator for…”). To buy with 100% certainty, confirm the wattage on the labels of your equipment.

(1) Essential home kit (emergency)

  • Refrigerator + router + LED lighting + chargers + TV
    ➡️ Typically, many people point to the 2–3 kVA range (especially inverter models, due to noise/electronics) — but confirm the refrigerator's peak current (critical point). (Peak current/motors: see Atlas Copco)

(2) House + some extras

  • Essentials + occasional microwave + extra lighting + laptop
    ➡️ Often, 3–5 kVA starts to make sense, depending on simultaneous usage and peak loads.

(3) Work/land (tools)

  • Angle grinder + drill + light + chargers + (sometimes) compressor
    ➡️ Here, the "villain" is usually the motor/starter: size it with a margin, because starting currents can be very high.

5) Gasoline vs. diesel: choose based on your usage.

A widely publicized rule of thumb in the rental/equipment industry:

  • Gasoline → more sporadic use and lower power output.

  • Diesel (diesel) → best suited for intensive use/high power

LoxamHune, for example, describes gasoline engines as suitable for occasional use and diesel engines as more powerful and ideal for intensive use.

6) Final checklist for buying (with purchase intent)

  • List consumptions simultaneously

  • Mark equipment with motor (peaks)

  • Apply a margin (e.g., +25% to account for peaks)

  • Always avoid letting your battery charge drop below ~30% for extended periods.

  • Choose the type: inverter (electronic/noise) vs. conventional (construction/simple use)