Django model to do accounting for a Litecoin miner pool
totalMachineHoursWorked should be a @classmethod.  It could be written more succinctly like this, using sum():

@classmethod
def totalMachineHoursWorked(cls, self):
    return sum(l3.indivMachineHoursWorked() for l3 in cls.objects.all())


However, I have doubts that any of the calculations should be done in Python.  totalMachineHoursWorked() needs to fetch the entire table.  I would recommend trying to find a way to do all of these calculations in SQL instead, because that's what SQL servers are designed to do: provide an efficient tool to let you extract aggregate reports by formulating your query intelligently.

In particular, if you need to calculate btcToHour() for multiple hosts, that would be horribly inefficient, since it would need to calculate totalMachineHoursWorked() multiple times, each of which involves fetching the entire table, and also performing a calculation on an individual row.