You might be referring to David Mackay's excellent 2008 book Sustainable Energy – Without the Hot Air - https://www.withouthotair.com
In the book he tries to determine if renewables could support UK's energy needs. He estimated the UK consumes about 195 kWh per day per person (food, transporation, heating, miltary defense, ...)
If the UK massively invested in all the renewable options it stacked up to 180 kWh per day per person (obviously he provided lots of caveats).
His assumption on Solar PV was covering 5% of the UK land with 10% efficient PVs (about 200m2 per person). He estimated that could contribute 50kWh/d/p.
In the 14 years since the book was published it seems like Solar PV efficiency is now commonly 17-19%. So might only need to use 2.5% of the land.
In the book he tries to determine if renewables could support UK's energy needs. He estimated the UK consumes about 195 kWh per day per person (food, transporation, heating, miltary defense, ...)
If the UK massively invested in all the renewable options it stacked up to 180 kWh per day per person (obviously he provided lots of caveats).
His assumption on Solar PV was covering 5% of the UK land with 10% efficient PVs (about 200m2 per person). He estimated that could contribute 50kWh/d/p.
In the 14 years since the book was published it seems like Solar PV efficiency is now commonly 17-19%. So might only need to use 2.5% of the land.