I believe Which magazine did a study, the conclusion being that it is actually cheaper to get the loan to do the work and keep the ‘feed in’ money yourself.
As far as storage goes, you effectively use the grid for storage.
This “won’t boil a kettle” nonsense is just headline grabbing rubbish, completely missing the point.
On a sunny day in winter they will work just as well as in summer, it’s light not heat that PV’s use.