Solar cells for sensors
What kind of "efficient" do you have in mind? Cost efficient? Efficient based on effort to get this done?

It is possible and certainly offers some benefits compared to other solutions (mainly you don't have to care about a battery replacement).

But it is a more costly solution. Specialized solar cells for indoor use and energy harvesting controllers are not the cheapest things out there - which you probably need if your system requires a more frequent upload of sensor data.

Depending on the requirements you might get away without a battery completely and replace it with a supercap, which will last longer and make your device run for many years.

Wifi as in Wireless LAN is probably a bit troublesome, which is why most commercially available systems use a low power wireless link (Bluetooth low energy and consorts) to a gateway which then provides LAN or wireless LAN powered from a wall outlet.

A lot of this really depends on your exact requirements. If it is an absolute requirement to use wireless LAN in the node and you need more then one or two updates a day, I'd probably look for a different solution.