Hi all,
I already got and tested the Pololu Mini LV power switch advised by jremington here in this post. It works perfectly and it is exactely what I was looking for. I have now first prototype of the watering system for the garden. Valve is automatically opening by the servo when watering needed. It communicate via NRF24L01 with the main node where Sigfox LPWAN module is also connected. Then the information about irrigation is transfered to the interent. Everything is designed to work on low power mode just with AA batteries to be able to use this system on places without external power source. I am looking forward to test it soon in the real environment.
Thanks for your help in this post.