Solar panels work best in summer when you probably don't need UFH on
So you can't really "link" them like this
But the hot water cylinder ( which the solar panels will provide heat to ) also functions as a heat exchanger between the boiler and the UFH pipework , so your thinking is not totally devoid of logic .
boiler - UFH
Solar - hot water
But in winter on sunnier days the solar will help the boiler . But this is a secondary consideration .