When I was updating this page the price was 27.89 USD for 5V 15W USB Solar (in Banggood). You can create price alert here, copy coupons and view price history. Do you want to know what the best price is?
Latest coupon code price check (UTC time):
Banggood (27.89 USD)
Banggood warehouse is located in China. I can’t find any active coupons for this product in Banggood. What about the price? Maybe there’re no more promotions for this item, because current price is higher than average (which is equal 26.76 USD)
Link: Banggood product page
Price: 27.89 USD
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
Old coupons (from the oldest to the newest): BG589b2e
(system checks these coupons on every price check (like once per 24 hours), but you can check them out anyway)
Aliexpress
Click here… to search for 5V 15W USB Solar Panel on Aliexpress
Here are coupons that you can use.
Price history and price alert
Check out price history chart (for all/most countries) for 5V 15W USB Solar Panel.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).