A propane company will only fill a tank to 80% of capacity. Therefore, a 500 gallon tank will offer 400 gallons of propane when filled. There is no guarantee the tank will be immediately refilled after each use, and having extra capacity compared to a 250 gallon tank (200 capacity) is a good move.
I installed a Kohler 20kw generator fifteen years ago. The engine is a Ford inline four cylinder which was a small commercial engine at the time. It has a 2000 watt block heater which adds about $60-$80 a month to the cost of electricity during the cold months.
Estimates are 2-4 gallons of propane per hour for a 14kw generator, and 4-6 gallons per hour for a 20kw depending on load.
My generator has been relatively trouble free, and for any issues I use Rowan Electric.
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