Extract from article on Generators

Committed to air conditioning ?

If you are committed to air conditioning 24 hours a day away from mains power, go for a straight 240-volt AC motor generator. If doing this for a substantial part of the time, consider using a diesel-powered AC unit such as the Onan CMQD. This is larger than needed for most purposes, but it's fine for mega-motorhomes with a couple of air conditioning units plus a big electric fridge. A diesel-powered unit will be a lot more expensive up front but will last forever and 40% or so less to run.

If you need air conditioning, but not all the time, go for the battery/inverter approach. It costs more initially but is hugely cheaper in fuel costs. Nor do you have to buy a motor generator large enough to start the air conditioner - because the inverter will handle the overload.

A 3000-5000 watt diesel generator costs about $0.80 for 1 kilowatt for an hour, and about 30 cents for every kilowatt an hour more: ie. running one air conditioner costs about $0.80/hour, running two at the same time costs about $1.10/hour. A further bonus is that many diesel motor-generators are water cooled - so you also have semi-free hot water!

A petrol-driven unit is likely to cost $1.20 for the first kilowatt/hour and about $0.50 per each kilowatt/hour over and above that. Running one air conditioner will cost about $1.20, running two at the same time will cost about $1.70 an hour.

If you start comparing AC generation with DC generation remember that much of the claimed fuel consumption difference may simply be due to the fuel they run on.

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