PhotoCrawl

At a party in Washington in November 1954 a general confided in Richard Feynman that what the army needed was a tank that ran on sand...

The entire global capacity to generate electricity is about 5 TW.

To give you some idea of how big that is, if you were to weigh all the electricity humans generate in a year (we're talking E = mc² here) it would come in at about two tonnes.  A year of the world's electricity weighs about as much as a small truck.

To give you some idea of how small that is, if you were to cover a 200 kilometre square of one of the world's deserts near the equator with solar photovoltaic cells, they would comfortably generate more than 5 TW, at least in the daytime.  That's an area slightly bigger than Devon and Cornwall, or Greater Los Angeles.  A square metre of PV cells costs less than a square metre of Los Angeles.

But we don't want to plod about in deserts laying down PV cells that we've made in factories on a different continent.  It's expensive and, worse, it's hard sweaty work.

PV cells are made of silicon.  A desert (to a first approximation) is also made of silicon.  Getting that silicon out and turning it into PV cells needs energy, of course.  But if you have some PV cells to start you off, you have some energy.

So.  Let's build an autonomous robot that crawls slowly over a desert shovelling up the ground and refining it into solar cells.  These it connects up and lays down behind it as it goes, keeping its own connection to them to power the refining process.

After many years the PV cells will lose efficiency as they get scratched by sandstorms and the like.  The robot could work in a continuous cycle, like painting the Forth Bridge, going back to its start point then grinding up the worn old cells and re-refining them back to brand new ones in its wake.

Free green electricity for everyone for ever...