[_carbyau_]

Even if it doesn't work for the UK. Australia could do this easily.

Proportionally less population, less snow covered territory and general coldness = easier requirements.

Land coverage? To say Australia has plenty of land is an understatement.

To amp up(excuse the pun) this mental exercise (don't mind the practicalities of building it!) a bit:

If efficient super-long distance power transmission was a thing, we could have batteries and solar for the whole world and locate it where few people would ever see it.

If placed into a single contiguous blob though, I imagine the solar panels would cause their own microclimate by sucking 20% of the suns energy out of many hectares/acres of land... so that may be a problem.