It will probably end up as a solar panel (measured in Watts) tax added on to the house tax.
This was once said about radio.
An intimate friend of Faraday once described to me how, when Faraday was endeavouring to explain to Gladstone and several others an important new discovery in science Gladstone’s only commentary was ‘but, after all, what use is it?” ‘Why, sir,’ replied Faraday, ‘there is every probability that you will soon be able to tax it!’”