The Economist usually takes a worldwide perspective; that's why this article uses US dollars and French kilograms and meters, because those are the most widely recognized units, even though the article focuses mostly on developments in the US.
As for your other comment, that air conditioning and spending US$2000 isn't "representative of the world," I think you will be very surprised if at some point you travel outside the US. The rest of the world does not consist of Elbonian mud farmers as you seem to think. Air conditioning is common throughout the warmer parts of the world; the majority of the world's population has access to air conditioning, though not always at home. The gross world product is about US$17500 per person per year, PPP.
"I think you will be very surprised if at some point you travel outside the US"
I'm not quite sure what prompted you to drag this down to that level. FWIW, I spent several years living in Europe and the Middle East. In homes that weren't air conditioned even. And a fair amount of travel to many other places.
"The rest of the world does not consist of Elbonian mud farmers as you seem to think"
Wow. You have no reason to go there. Fuck off. Saying that lacking $2k of discretionary money to spend on lithium batteries is "Elbonian mud farmers". Wtf. I've certainly had times I my adult life where I didn't have $2k of discretionary money.
Haha! I didn't realize you were imagining a battery bank as some kind of toy. I was thinking more like an alternative to a gasoline generator, which is not really "discretionary spending".
As for your other comment, that air conditioning and spending US$2000 isn't "representative of the world," I think you will be very surprised if at some point you travel outside the US. The rest of the world does not consist of Elbonian mud farmers as you seem to think. Air conditioning is common throughout the warmer parts of the world; the majority of the world's population has access to air conditioning, though not always at home. The gross world product is about US$17500 per person per year, PPP.