Generator Runtime & Fuel.

Add up the running watts of everything you'll power (PA, lighting, catering gear) and convert to kW, then size the generator so that total load sits at roughly 50 to 75 per cent of its rated output. Generator ratings are usually given in kVA, and a rough rule is rated kW equals kVA times 0.8, so a 20 kVA unit is about 16 kW. Leaving headroom protects against startup surges from motors and the wet-stacking that comes from running a diesel set too lightly.

kVA is apparent power (the total the alternator has to supply) while kW is real power (the work actually done), and the gap between them is the power factor. For typical AV and event loads a power factor of about 0.8 is the standard assumption, so multiply kVA by 0.8 to get usable kW. Always size against the kW figure, because that is what your gear actually draws.

Fuel burn depends mostly on the load, not the generator's badge size, so a lightly loaded set sips fuel while a heavily loaded one drinks it. As a teaching figure, a diesel generator burns roughly 0.25 litres per hour for every kW of load it is actually carrying, plus a small idle amount just to keep running. For an accurate figure for a specific machine, check the consumption curve on its data sheet, since engine age, altitude and load profile all shift the number.

Divide the usable tank size in litres by the fuel burn in litres per hour at your expected load. A bigger load empties the tank faster, so the same machine might run all day on a light show and only a few hours flat out. For an all-day or overnight event, plan a refuelling stop or a larger long-range tank rather than risking a mid-show shutdown.

Yes. Running a diesel set well under about 30 per cent of its rating for long periods causes wet stacking, where unburnt fuel and soot build up in the exhaust and glaze the cylinders, hurting reliability and performance. The fix is to size the generator closer to the real load or use a load bank, which is why oversizing 'to be safe' can actually do more harm than good.