mj/hr to kg/hr for a LPG systems

I was looking at Gas powered Electricity Generators today, and needed to work out the LPG consumption from the quoted mj/hr figures being quoted in the product specifications.

The figures quoted, for both LPG and Natural Gas were:
LPG: 73.8Mj/Hr
NG: 75.2Mj/Hr

I did find that 1kg of LPG was equivalent to about 50MJ of LPG energy.

So a standard 8.5kg LPG gas bottle would last for about 5 hrs 45 minutes at full power producing 4.4KW of constant power.

So… about 25 kilowatt hours for $20 LPG cost, or almost 80 cents per hour per kW, using that particular generator.