Photovoltaic system that charges a Li-Po battery while supplying a 1.4V load
To switch between battery and PV array based on availability, you can use an active OR'ing controller. TI, for example, has a wide variety of those and some designs using discrete components have been discussed on this forum as well.
This will allow you to have a battery charging stage and a PV stage. When there will be sufficient power going from the PV panel, your load will draw it from there and not the battery; when there will be no PV power the load will draw power from the battery.