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

This is way outside the normal rooftop solar scale.  But here are my thoughts.

It's not unusual to have en inverter that's under-sized compared with the kWp figure from the panels.  It means that on a bright sunny day, the inverter will attempt to MPPT, but eventually will hit the maximum power that the inverter itself can deliver.  Yours seems a rather extreme example of doing that.

If you're operating in a cloudy country like the UK, don't assume that 1MWp of panels can reliably deliver 100kW.  If you have a grid-forming (i.e. islanded mode) inverter, then the output could collapse suddenly if the demand exceeds what the panels are supplying.  That's a really good reason to add a battery.

Simon Barker said:

If you have a grid-forming (i.e. islanded mode) inverter,

Is this to be grid forming of the National Grid kind, which looks to mimic rotating machine generation, and HV transmission transient problems, or some other sort of limited grid? 

There's a lot of Catch 22 discussions go on about which parts are 'cause' and which are 'effects', and which are dominating and which are incidental. Historically inverters were incidental to the grid...

I hadn't thought of that.  A single inverter can run in "islanded" mode.  But there's also the possibility of using an inverter to "black start" a local microgrid.

That's way outside my expertise.

I hadn't thought of that.  A single inverter can run in "islanded" mode.  But there's also the possibility of using an inverter to "black start" a local microgrid.

That's way outside my expertise.