Like MikeyB suggests, you'll most certainly need a battery as bridge between the panels and the RPi, most of the time the panels will only prolong the battery life, I don't think the panels alone will supply enough current for display, RPi, + computing, + your connected hardware. Unless you have pretty big panels and during solstace under a clear sky.
There is no reason the HDMI display shouldn't work really, assuming that the RPi has a fully functional HDMI connection (some pins are designated external power rails and in theory they could be left out since they're not being used when you plug in to just a generic HDMI device with it's own PSU).
@What MikeyB said:
The DSI connector on the RPi for LCD modules is still kind of a mystery (no documentation released on it yet to my knowledge at least) and the disadvantage with that, should you get a LCD module with the correct size DSI connector and data interface, in 95% of the cases those modules need 12V LED backlighting, now you will have to build your own DC-DC step-up converter, or buy one.. The HDMI "plug and play" option is already starting to look quite attractive.
Have you found such a monitor that can be used with only HDMI input? It would be nice to share.
Also from a bit of personal experience, if you are going to use a desktop environment you might want to get a big enough monitor, 640x480 would be the absolute minimum usable in my opinion, I've used 800x480 and a lot of desktop applications are not resizeable small enough to fit completely vertically (480 pixels is the let-downer) but it's just about enough.