Generator sizing for UAE sites: kVA, load and standby explained
Undersize and you trip the set, oversize and you waste fuel. A full guide to kVA, power factor, prime and standby ratings, and the headroom UAE heat demands, with a simple sizing method.
8 min read · 2026-06-27
Generator sizing is a balance, and both ways of getting it wrong are expensive. Pick a set that is too small and it trips under load, runs hot and ages fast. Pick one that is too large and it sips fuel inefficiently and wet stacks at low load. The right size comes from three things: your load profile, the rating you need, and a sensible margin for UAE conditions.
None of it is complicated once the terms are clear. This guide explains how to read your load, what kVA and power factor actually mean, the difference between prime and standby ratings, and how to leave the headroom the heat demands.
Size for the peak, not the average
The set has to swallow the largest starting surge without the voltage sagging. The peak demand matters as much as the steady running load.
Start with your load profile
List everything the set has to feed and how it behaves. A steady lighting and small power load is easy. Motors, pumps, compressors and air conditioning are not, because they draw a large surge as they start. The set has to carry that starting surge without the voltage dipping, so the peak demand drives the size as much as the steady running figure.
kVA, kW and power factor
These three terms cause most sizing mistakes, so it is worth being precise about them.
| Term | What it is | Why it matters |
|---|---|---|
| kVA | Apparent power, the set rating | How generators are sold and rated |
| kW | Real power that does work | What your equipment actually consumes |
| Power factor | Ratio of kW to kVA, around 0.8 | Links the two; a 1250 kVA set gives about 1000 kW |
| Starting surge | Peak draw as motors start | Can dwarf the steady load and must be covered |
Size against kW for the real load, then confirm the kVA rating covers it. Mixing the two units is the classic way sizing goes wrong, leaving a set that looks big enough on paper but is not in practice.
Prime, standby and continuous ratings
- 1
Standby rating
Highest output, but only for the duration of an outage. Use for backup sets that rarely run.
- 2
Prime rating
For variable load over unlimited hours with no grid. This is the site rating for most projects.
- 3
Continuous rating
For a constant load running around the clock, such as a fixed industrial duty.
Headroom and UAE heat
High ambient temperature reduces the output a set can safely deliver, so a unit rated in a cool test bay gives less on a hot site. That derating is real and has to be built into the sizing. The chart below shows the pattern indicatively: as the ambient climbs, usable output falls.
0.8
typical power factor
70-80%
target load on a prime set
Prime
rating for most sites
Heat
cuts usable output
Do not run at the limit
Loading a prime set to around 70 to 80 percent leaves room for starting surges, future load and the heat. Running flat out with no margin is where reliability problems start.
A simple sizing approach
- 1
Total the load
Add the running load in kW, then add the largest starting surge.
- 2
Convert to kVA
Use a power factor near 0.8 to check the set rating covers it.
- 3
Pick the rating type
Prime for most sites, standby for backup only.
- 4
Add headroom
Allow for heat and growth, then confirm against derated figures.
For larger or continuous loads, two smaller sets paralleled often beat one large unit, giving redundancy and efficiency. Send us the load list and we will size the set, the distribution and the fuel plan together.
Need this on a live job?
Send the spec and dates. Indicative rate back in minutes, certified crews and clearances handled.