Saturday, February 2, 2013

Why this is Wrong... "In six daylight hours, Earth’s deserts soak up more energy than humanity uses in a year. "

I hate this quote -"In six daylight hours, Earth’s deserts soak up more energy than humanity uses in a year."  It is often used by solar energy companies to drum up support.  I don't have a problem with solar energy,  but I hate when people use confusing comparisons just to prove their point.  It's like saying that "This skyscraper weighs 150 blue whales, and is 15 giraffes high".  Aka it makes no sense.

Numbers (the wrong way):

Deserts on earth:  -all land 150,000,000 km^2, deserts ~ 1/3 of land = 50,000,000 km^2

Insolation for the 6 hours around solar noon near equator: 1300 W/M^2

Energy use of earth for year: 143,851 TWH (terra watt hours)
= 143,000,000,000,000,000 WH(watt hours)

For those 6 hours: 50,000,000,000,000 M^2 (of deserts) X 1300 W/M^2 X 6 Hours
= 390,000,000,000,000,000 WH

390 PetaWatt Hours  is more than double 143 PetaWatt Hours
Wow so much power!!!

Numbers (more correct):

Deserts on earth: 50,000,000 km^2 - 13,700,000 km^2 (antarctic) - 13,800,000 (arctic)
-We are not going to put solar panels up in these deserts.  It would be dumb.
= 22,500,000 km^2

Insolation for 6 hours around solar noon: 750 W/M^2
- 1300 W/M^2 is what we get from the sun at the top of the atmosphere.
- deserts are not all at the equator (but most included are close)

(2.25 X 10^13 M^2) X (750 W/M^2) X 6 Hours=  1.01 X 10^17 WH

Uh oh!!  Now it seems that we get 101 PetaWatt hours from those deserts in the 6 hours, while we use 143 PetaWatt hours....

Oh Noes!!  Here comes some more reality!!

The efficiency of solar cells ( in super happy land ) : 40 %
Land use efficiency of solar power farms (efficient ones): 50%

So this brings us to 101 PetaWatt Hours X 0.4 X 0.5 =  20.2 PetaWatt Hours

But wait, there's more!!
Transmission losses and storage losses!
~ 6% loss in transmission (best case)
~ 5%  loss in storage and discharge from battery (best case)

20.2 PetaWatt Hours X 0.95 X 0.94 = 18.1 PetaWatt Hours

So if we cover all of the available deserts in the world with solar farms, it will take about 48 hours of  sunlight at noon to supply the world for a year.  This is nearly a tenth of the surface of the Entire Fucking Earth.  Fuck,  Humans are Fucked.
Fuck me, I'm a human.


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