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Lecture 33

# EPS 7 Lecture Notes - Lecture 33: Radiant Flux, Polycrystalline Silicon, Ingot

2 pages42 viewsFall 2017

Department
Earth And Planetary Science
Course Code
EPS 7
Professor
David Romps
Lecture
33

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Lecture 33
Solar power: ready to save the day?
1. Sio2 O2 + Si in a furnace
2. To make a thin wafer of silicon, first melt the silicon chunks
3. Then either let the liquid freeze in the container, (polycrystalline silicon)
- Close up of a polycrystalline PV panel
4. Or grow a single crystal out of the melt
- Silicon ingot, a single crystal that can be sliced to make wafers
1) Thin film
2) Mono silicon
3) Polysilicon
Solar cells, also known as photovoltaic cells, or PV cells, convert sunlight directly to
electricity
A light-emitting diode (LED) can convert light to electricity
LED and PV work on the z same principle
There is a layer of silicon connected to wires and that layer forces electrons to move
one way only
Recall that Earth’s TSI is 1360 W/m2
But, due to absorption and scattering, average isolation at the ground is roughly 1000
W/m2
That is 1000 W/m2 facing the Sun.
- High latitudes get less sunlight per ground area
But we can just tilt the PV panels
Tilting PV panels gets more power per panel area, but does not get more power per
land area
Factoring in everything: about 100-200 W/m2 at the surface
Let us call 150 W/m2 a typical solar flux at the surface
How much energy could be made if we covered all land in PV
With what efficiency does PV convert this to electricity?
Let us call 20% a typical PV efficiency
Solar flux at surface: 150 W/m2
Efficiency of PV = 20%
150 W/m2 x 20% = 30 W/m2
Land area = 150 trillion m2
30 W/m2 x 150 trillion m2 = 4500 TW
ENORMOUS!!
How much area of PV is needed to meet all future needs?
We have two numbers:
60 TW and 30 W/m2
(60 TW) / (30 W/m2) = 2 T m2 = 2 trillion m2
Remember, total land is 150 trillion m2
So we need about 1% of the Earth’s land area
Needed: 60 TW
Max from wind, hydro and biomass
Solar PV on 1% of the land: 60 TW
Area of Mexico: 2 trillion m2
Is it sufficient to have PV on our roofs?
What is the area of a house’s roof?
a. 1 m2 1x1 size of a table
b. 10 m2 3x3 size of a shed