Using solar with a 3 phase motor to generate stable 3 phase current
For powering 3-phase motors, it is probably best to use motor-control inverters, also known as variable frequency drives (VFDs). They can start the motors with no or very little extra current required during starting. You should be able to find VFDs that will accept 300 V dc input. 

It sounds like you may have been planning to use the 100 Hp motor as part of a phase converter setup. You wouldn't need that, but you would need a VFD for each 3-phase motor. It is possible to use one VFD for more than one motor if the motors would always be running at the same time. If only one motor is running and you need to add another, you would need to stop the first motor, connect the second and restart both.