here is my contribution for solar powered RPI projects.

using a raspberry Pi for small projects that are solar powered you can use a powerbank with pass through charging for powering the RPI.

the **power path** can be
solarpanel  -->  powerbank   -->  RPI 1/2 /3 + wlan stick

**requirements**
*solarpanel*  
voltage  5V / current 2A / power output 20W, monocrystaline Modules 
for example SunPower Modules with USB connector
*powerbank*  
voltage 5V / current 2A / capacity 20Ah


**advantages**
- ups function for RPI
- the RPI works 24 hours a day powered by the powerbank
- the solarpanel delivers power that can be saved in the powerbank


**possible solarpanel**
[RAVpower 24W Solar Charger](https://www.amazon.de/gp/product/B01EXZWRAI/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1)
![solar charger](http://www.ravpower.de/media/61kj5oijYsL__SL1000_.jpg)

**possible powerbank**
[RAVpower 22Ah Powerbank](https://www.amazon.de/gp/product/B012V88B90/ref=oh_aui_detailpage_o00_s01?ie=UTF8&psc=1)
![powerbank](http://www.ravpower.com/media/pic/65-02052-001-1.jpg)

with a **usb multimeter** you can measure the power output of the solarpanel
[USB multimeter](https://www.amazon.de/X-DRAGON-Multi-Moniter-Leistungsmesser-Leistungsmessger%C3%A4t-Amperemeter/dp/B01AW1MBNU/ref=sr_1_1?s=ce-de&ie=UTF8&qid=1470591779&sr=1-1-spons&keywords=usb+multimeter&psc=1)
![USB multimeter](https://images-na.ssl-images-amazon.com/images/I/41WJYdy8NsL.jpg)