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

2 pages42 viewsFall 2017

Department

Earth And Planetary ScienceCourse Code

EPS 7Professor

David RompsLecture

33This

**preview**shows half of the first page. to view the full**2 pages of the document.**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

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