Aliexpress
Here are coupons that you can use.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China. There is one great coupon!
Link: Banggood product page
Coupon (114.07 USD): BGNEWYEAR8
(CouponsFromChina.com tip: you should apply the coupon in your cart after clicking “Proceed to checkout”. Click to copy code and open shop)
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
Old coupons (from the oldest to the newest): BGdcbfa8, BG8ReviTrage, BGa21ac1, Cuponation9, BGCarEle4, BG18offso, BGCarEle5, BGe07582, BGSCM11, BG845979, BGLMQ15, BGCAR639, BGb29a4b
(these coupons are old, so probably won’t work)
Price history and price alert
Check out price history chart (for all/most countries) for CKSF60 60W 18V Shingled Solar Panel.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).