Solar panel and LiPo is very popular and components are "off the shelf" at the usual suspects. SparkFun, Adafruit, Pololu, and Seeed to name a few - they have different panels, chargers, regulators, and Li cells so you may want to check more than one and mix and match.
I would suggest getting one size larger than you think you need. This will allow for mistakes in computing what you need or one level of feature add on later.