Chapter 3 How are photovoltaic systems made?

Question 1

Photovoltaic Device Fundamentals ?

Answer 1

1) Charge Generation:
Light gives electrons enough energy to escape from their valence band to the conduction band
2) Charge Separation :
the fact that we put a N-type next to the P-type, we induce an electric field that allows for a potential to build up within this PN region that acts as a barrier stopping the charges ( + / - ) .
3) charge collection :
Electrons are freed by Photon energy in the edges of the N region , a short circuit is applied from N regions to P regions , electrons go through that , depositing their excess energy into an external load rejoining then the P region looking for a hole to fill

Question 2

I Generation
Bulk Crystalline
Silicon , advantages and disadvantages ?

Answer 2

Advantages
• High efficiency 15-20 %
• High stability
• State of the art

Disadvantages
• Rigid / inflexible
• Require lot of energy in production

Question 3

From Silica to metallurgical Grade Silicon ?

Answer 3

Carbothermic reduction: SiO2

s) + 2C(s) = Si(l) +2CO(g

Question 4

From metallurgical Grade Silicon to Solar Grade Silicon ?

Answer 4

Siemens Process ,
1 kg SG – Si by the Siemens Process: 4,4 kg MG Si are needed.
• 19 kg CO2 are emitted through that process
* consumes energy : 176 kWh / kg

Question 5

From SG Si to Monocrystalline Ingot ?

Answer 5

different methods , but principle remains the same , heating the SG Si by induction and then process to immediate cooling

Question 6

Wafer to Solar Cell

Answer 6

1-Saw damage removal
2-Texture etching
3-p-n junction formation
4-Antireflection coating
5-Metallization (contact printing)
6-Firing of contacts

Question 7

Generation III organic modules ? pros and cons

Answer 7

Pros :
• Low materials consumption
-
*Band gap tunable ( further explanation on the slides )

Cons :
Low efficiency
• Degradation under UV

Question 8

Generation II : thin film solar cells pros and cons ?

Answer 8

pros :
• Flexible modules – versatile utilization
-Engineering of light spectrum to harvest
Cons :
Lower efficiencies
Scarce elements sometimes used

Question 9

Generation II Cadmium Telluride pros and cons :

Answer 9

pros :

Most economical thin film
technology currently available
• long-term stability

Cons : 
Tellurium – questionable
abundance
• Cadmium is very very toxic – questionable
marketability