Hi, Kimi xiong,
I believe you are linked with this Drone company?
http://www.hk-huijun.com/index.asp
We here use a small drone here for checking the fields and animals, sheep/cows stuck in hedges/streams etc, as we have undulating land and steep valleys, with lots of trees and big hedges.
We particular like the .......... Hubsan 0.41Kg in total weight.
Hubsan H501S H501SS X4 Pro 5.8G FPV Brushless Avec 1080 P HD Caméra GPS RTF Suivre Me Mode Quadcopter Hélicoptère RC Drone .........
I use Alliexpress .. ...
https://www.aliexpress.com/wholesale?catId=0&initiative_id=AS_20181101002426&SearchText=hubsan+h501s+x4
Why? because its small compact has a range of 3 to 4 miles, auto returns if signal lost, 20 minutes of flying time, has a excellent good LCD screen, good stable flight ..... and importantly its under $300.
My 14 year old fly's, as it has a multitude of mode operations, far to complicated for this old duffer.
Personally a small spotter drone is excellent for Solar arrays, and has little chance of breaking PV panels, we have experimented with the Hubsan.