But do they give people an understanding or a false impression?  If say, a new wind farm is said to be able to power 5 million homes, some people might work out  that with 26 million homes in the UK that is roughly one fifth of household demand.  But what about industrial and other demands?  It does not say anything about those.  If we assume that one Home is equivalent to 400W, then 5MHomes is 2GW.  Total UK average demand is about 35GW.  Would it not be better to say that it will deliver 2GW which is 6% of current demand?  And then of course there is the additional demand once we decarbonise all of industry and transport.  

I have only just noticed this interesting discussion.

A "home" could be a studio flat in a modern well-insulated block, or a 10-bedroom Victorian residence with next to no insulation so it is IMHO, a rather meaningless concept.

A standard football pitch (round or oval) is 100 m long so for me, that is a reasonable unit of measure.

Average domestic consumption is no more use to me than an average home. What I am interested in is my own yearly consumption, which fell last year, but perhaps the winter was mild.

"A home" is generally reckoned to be about 1 kw though this is rather flexible depending on whom is trying to prove what.