KisekiMaybe, but only with it off (and very slowly even then) - keep in mind that the Surface 3's native charger delivers 13W (although it is micro-usb and not a 12V input).
KisekiDoesn't look like it's ideal or recommended. See their answers in the Q&A section here: http://www.goenerplex.com/products/portable-solar-chargers/kickr-ii
Bottom line - this product doesn't include a built-in battery bank, so the energy supplied is affected by the quality of sun exposure. They have other products with the solar cell charging the battery bank, then the battery bank delivers a consistent stream of energy for charging.