Here's one option for connecting a solar panel to Pinoccio. I used an Adafruit solar LiPo charger. This board has a 'Load' output, but since it could be anywhere from 6V (the maximum of the panel I'm using) to 3.1 V (the low voltage LiPo battery cutoff), it can't be connected directly to the VUSB input of Pinoccio.
The charger's 'Battery' outputs 3.1-4.2 V and so can be connected to Pinoccio's VBAT, but requires an adapter cable. Pinoccio uses a JST-SFH connector for the battery, while the solar LiPo charger and many LiPo batteries use the JST-PH connectors (a link to sourcing the JST-SFH connects is on the topic http://discuss.pinocc.io/t/recommendation-for-battery-socket/81). I soldered up a Y-cable to attach both the Pinoccio and a LiPo battery to the charger board. A separate adapter cable converts JST-SFH to JST-PH so that I can use the default Pinoccio battery if I wish.
The JST-SFH sockets seem to only be available as surface mount parts. The leads can be carefully bent up in order to solder wires to them; bending more than about 45° risks breaking the lead. On my adapter cable I added an extra outer shrink-wrap layer for strength; hot-glue could be used as well.
The maximum output of the LiPo charger is set to 500 mA (this can be changed), but the panel can only output a maximum of ~330 mA in bright sun, so it's safe for the Pinoccio battery or a larger one. Note that the Adafruit 2W solar panel requires a barrel jack adapter to plug into the charger jack. A larger battery will allow continuous operation during a string of cloudy winter days.
This modification bypasses Pinoccio's onboard LiPo charging chip, but I think that the MAX17048 will still read accurately since it uses battery voltage.