I know for a fact Photosynthetic doesn't fulfil its light requirements at night, since I had it at one point diving Red Rock and I came out at nearly starving in the middle of the night and before morning got to actually starving. Granted, it lasts a LONG time even at level one, though Grit Gate could be an issue if you don't have a recoiler for it yet.
As for solar cells vs chem cells, the charge REALLY makes a difference in some applications. For instance, Force Bracelets, an item that gives you basically the best defensive mutation in exchange for cell power, only lasts about 5-6 turns with a full solar cell. While for things like recoilers, if you have two solar cells, you can blip between joppa and grit gate without worrying about recharging chem cells ever. Then there are weapons. Certain weapons use far more power then can be stored in a solar cell, and even use up most of a chem cell (I'm looking at you Nullray Pistol and Freezeray Pistol). While others don't need the storage in chem cells, since you get a ton of shots out of even solar cells.
Then there is the last part. A warrior type with no int can recharge solar cells on his own, while you need tinkering skills to recharge chem cells, or pay people to do it. Not a bad thing, per se, but it does make Solar cells a bit more useful for the general populace of classes.
As an aside, WTF do nullray pistols do? They seem to do no damage, take a MASSIVE amount of charge per shot, and typically cost nanomaterial to make.