Before hiring a generator, it's important to know what type you need. Consider if it's for mobile or permanent use, standby or prime source of electricity, and if it will be used occasionally or constantly. These factors will help identify the right supplier and the right solution.
To determine how much power you need, you should consider both real (KWe) and apparent (KVA) power. Generating sets are specified at 0.8pf, so a 500KVA generator may only provide 400KWe of power. You should also consider the way in which power is required, as some equipment may have differing loads when they are first started.
When specifying a generator, you need to know how sensitive your electrical equipment is to changes in supply, both in terms of voltage and frequency. Generating sets are supplied at a number of performance classes, which define their stability for voltage and frequency under steady load conditions and under conditions of changing load.
Generators can be powered by a wide variety of fuels including Diesel, BioDiesel, Petrol, Natural Gas, and LPG. The most common fuel for standby power is diesel, owing principally to storage stability, cost, and availability. It's important to consider the type of fuel as it determines the type of engine.
The environment in which the generator will operate can affect its performance and constituent components. Factors such as ambient temperature, altitude, and humidity should be taken into consideration. You should also consider the physical environment in which the generator will be located, as generators have many inherent hazards and produce hot exhaust gases and noise. Much legislation applies to this in the UK and across Europe.