Can I run a 100kW inverter off a 1MW busbar?

You have not said why you find yourself contemplating this - and I should say this sort  of power is well off the end of my experience too, but it seems a slightly odd thing to do.
It is fair to say that in the UK, a nominal 1kW panel rarely does generate the full 1kW output , so it is standard to have an inverter that looks slightly undersized relative to the panel array full power rating, especially if the array is not optimally aligned for midday sun.  However unless you are expecting to stack up five or more  such inverters, with a ten to one ratio,  the bulk of your power will be lost on sunny days and the MPPT circuit will spend a lot of time bumping on its upper limits, which is not really making best use of the panel array. You do not say how the bus voltage is derived - are there additional balancing inverters on sub groups of panels ?

As an aside to your question, but an area I know more about, large inverter type installations need to be thought out very carefully in terms of cable routing and if need be additional filtering  to avoid creating EMC interference problems. It is very easy to create accidental loop antennas, and the more amps in circulation, the more they radiate harmonics of the switching frequency/ frequencies and the more there are the more likely the site as a whole is likely to exceed emission limits. Enforcement is not usually very strong in the UK but that does not make it the responsible thing to do.
So, what  is the driver for considering this approach ? 

Mike

You have not said why you find yourself contemplating this - and I should say this sort  of power is well off the end of my experience too, but it seems a slightly odd thing to do.
It is fair to say that in the UK, a nominal 1kW panel rarely does generate the full 1kW output , so it is standard to have an inverter that looks slightly undersized relative to the panel array full power rating, especially if the array is not optimally aligned for midday sun.  However unless you are expecting to stack up five or more  such inverters, with a ten to one ratio,  the bulk of your power will be lost on sunny days and the MPPT circuit will spend a lot of time bumping on its upper limits, which is not really making best use of the panel array. You do not say how the bus voltage is derived - are there additional balancing inverters on sub groups of panels ?

As an aside to your question, but an area I know more about, large inverter type installations need to be thought out very carefully in terms of cable routing and if need be additional filtering  to avoid creating EMC interference problems. It is very easy to create accidental loop antennas, and the more amps in circulation, the more they radiate harmonics of the switching frequency/ frequencies and the more there are the more likely the site as a whole is likely to exceed emission limits. Enforcement is not usually very strong in the UK but that does not make it the responsible thing to do.
So, what  is the driver for considering this approach ? 

Mike