Chip McClelland @ hackster.io published his solar li-po battery charger based on MCP73871 to manage the solar and DC charging of the LiPo battery, TPS63020 Buck-Boost Converter and Maxim 74043 LiPo Fuel Gauge. He writes:
I build connected sensor which are often deployed in local parks where there is no access to utility power. Over the past couple years, I have been refining and testing my solar power modules and have arrived at this compact integrated design. I have a number of these deployed and they have been in continuous service for up to two years. I wanted to share this design in case it might be helpful for your projects. I would also greatly appreciate any input or suggestions on this design so v3 will be even better.
Solar Power Module v2 – [Link]