C.4 – Solar Energy
NOS-How Important are Scientists?

“ As experts in their particular fields, scientists are well placed to explain to
the public their issues and findings. Outside their specializations they may
be no more qualified than ordinary citizens to advise others on scientific
issues, although their understanding of the processes of science can help
them to make personal decisions and to educate the public as to whether
claims are scientifically credible.”

IB Chemistry syllabus, Nature of Science statement 5.2
What are Some Forms of Solar Energy?
Photosynthesis Review

What do you recall about photosynthesis from Biology?

Where in the plant cells?

Balanced equation?


6 CO2 + 6 H2O  C6H12O6 + 6 O2
Why do plants appear green?
Plant Pigments: Conjugated Structures

Alternating single and multiple bonds
Plant Pigments

Violets
Plant Pigments

Purpurin (1,2,4 – trihydroxyanthraquinone)

Rose madder plants
Biochemistry!!!
Biofuels

Ethanol

Fermentation of corn sugar or glucose
C6H12O6  2 C2H5OH + 2 CO2

Carbon neutral
Biodiesel

From vegetable oils

Similar amount of energy as diesel from combustion

Viscous – why?

clog fuel injectors

Incomplete combustion
Transesterification

Convert to less viscous esters

Shorter-chain alcohol, strong acid or base catalyst

Usually sodium or potassium hydroxide catalyst and methanol  methyl ester

Ethanol (with base catalyst)  ethyl ester
*Not perfect. Some fatty acids remain.
Sample Problem

Deduce the equation for the reaction of pentyloctanoate with methanol in the
presence of an alkali catalyst.
Comparison of Diesel to Biodiesel

Table 1 (pg. 677)
Book problems

Pg. 678 – All of them!
C.8 Photovoltaic and
Dye-Sensitized Solar
Cells (HL)
Describe the bonding and hybridization
in Conjugated Structures

Retinol

β-carotene
Electron
Conjugation
Conjugation and Wavelengths

More conjugation = absorption of longer wavelengths
Retinol = absorbs
400-420 nm (violet)
 See yellow
B-carotene = absorbs
430-480 nm (blue) 
See orange
Sample Problem

An indicator has a red form and a yellow form. Deduce which of these two
colors is due to a molecule with a higher degree of conjugation.

Yellow violet (400-420 nm)

Red  green (490-575 nm)

Red = higher degree of conjugation
Conductivity

What types of elements are good conductors of electricity and why?

Relate to Ionization Energies!

What about semiconductors like Si?

Temperature and conductivities?
Photovoltaic Cells

Silicon-based semiconductors

N-and P-semiconductors

https://www.youtube.com/watch?v=1gta2ICarDw
Dye-Sensitized Solar Cells (DSSC)

Grätzel Cell

Dye (berry juice)

TiO2 nanoparticle semiconductor

Anode (transparent – glass)

Cathode

Iodine solution (I-)

Circuit
Diagram of DSSC

Ms. Hall’s Diagram

Figure 7, pg. 714
Explain Efficiency of DSSC…

Why nanoparticles interacting with dyes instead of larger substances?

Why darker (purple, red, even black dyes) dyes?
Advantages and Disadvantages of DSSC
vs. Photovoltaic Cells
Advantages
Disadvantages
Cheaper
Not viable for large-scale applications
Lower energy (longer wavelength) light
Electrolyte can freeze at low temps
Cheap, easy, renewable resources
Expand/crack at high temps
Nanoparticles = higher absorption of
light
Conductivity higher because of TiO2
mesh
Thin layer (flexible, durable, radiates
heat way better)
https://www.sciencedaily.com/releases/2017/04/17041
8114514.htm
Book Problems pg. 716 – Due Monday
(Extra Credit)

#2-4

*look over the rest (1 and 5)