Aliexpress
Here are coupons that you can use.
Other warehouses/versions
This item is available in 1 another warehouse/version!
1. Europe – iMars SP-B21 21W Solar Panel [EU] (-3 USD)
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China. One coupon is available. Cool!
Link: Banggood product page
Coupon (50.99 USD): BGCarEle4
(CouponsFromChina.com tip: paste coupon code in your cart and click Apply 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): BG6ff0c1, BGe3cbdf, ADMITAD2212, 2022ACTIESNL, BG2Y0081, BG31dfbd, BGSO616a, BGCarEle1, BGf2bb2c, MVC8SPRING, BG7b0218, BG8760f8, BG8950bd, BG20iMars, BGdcbfa8, BG989657, BG2999SP, BGRSUNSPB21, BGHUXC121, BG12dbc0, BG5994f4, BGHU162d, BG3346a8, BGHU2344, BG66d7dc, BG015570, BG0aa4d4, BGiMars2022, BGCarEle5
(you can check these old coupons out, but these probably won’t work)
Other warehouses/versions
This item is available in 1 another warehouse/version!
1. Europe – iMars SP-B21 21W Solar Panel [EU] (-3 USD)
Price history and price alert
Price history (for all/most countries) for iMars SP-B21 21W Solar Panel is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).