Solar inverters could simulate inertia by not running at 100% most of the time, but you do want the free energy machines to run at 100% as much as they physically can, because it's free energy, which means there's no buffer for simulating inertia. It's been commented many times that batteries can be used to simulate inertia. You can also literally just add inertia, in heavy spinning lumps of metal that don't do anything.