How to connect battery and solar panel in parallel to power load?
Yikes. That site is icky.

You cannot simply connect 10 V to a LiPo battery. That is a good way to get an explosion/house fire/sad battery/sad you. LiPo batteries (and several other battery chemistries) require CC/CV charging, meaning they need constant current charging up to a float voltage, and then constant voltage charging after. 

Another issue is that you cannot simply connect a solar panel to the input of that circuit. Solar panels do not provide a fixed voltage (it varies with sun intensity) and operate with poor efficiency unless you put in a little extra effort to do maximum power point tracking.

It sounds like you want to build a solar-powered battery charger circuit. Luckily, there are existing solutions that make this task easy. There are many ICs that are both MPPT controllers and multi-chemistry battery chargers. For example, the Linear LT3652, which is suitable for small panels/smallish batteries (max charging current 2A). As is characteristic of Linear parts, the datasheet is quite good and provides a wealth of information on how to design for various battery chemistries and load configurations.