Hi Kristof, in the mean time I send a question to TPLINK support about this. They confirmed that the HS110 is NOT suitable for measuring power generated. I have send the (not-smart-enough;))plug back...

Model : HS110(EU) Box also lists Ver:2.0 Hardware Version : 1.0 (Kasa App Firmware Version : 1.2.5 ISP : Hi, I have a HS110(EU) V2 Smart Plug and connected my solar panels. I can not see the power...