Transcript Chemical Challenges in Renewable energy

Challenges in the incoming energy scenario: role
of chemical sciences
SERGIO CARRA’
Mean global energy consumptions
Total 13.8 TW,
US 3.3 TW,
Italy 0.25 TW
The less expensive fossil sources represent the
lion’s share!
Can we supply the energy needed in the future with
fossil fuel?
Quite probable yes.
Than it appears that renewable resources will not play a
large role in primary power generation unless, or until:
. Cost breakthroughs in carbon-free
technologies are achieved.
. Externalities are introduced , such as
environmentally driven carbon taxes.
Actually also if there are reassuring resources of fossil
fuels, geopolitical and regional factors can affect
significantly the price of energy.
•Current
•By
global energy consumption = 13.8 TW
2050 consumption = 25 TW. Need abot 10 TW.
–Fossil
fuels: Can produce extra 10 TW only at risk to
environment.
–Wind/Geothermal/Biomass/Hydroelectric:
Cannot
produce 10 TW. (But should be implemented where
appropriate: energy is extensive)
–Nuclear:
Requires massive investment today to
provide power plant infrastructure (10 TW = 10,000 new
1 GW reactors, in 50 years).
Carbon dioxide sequestration
The employment of geological reservoirs is potentially
feasible but it arises problems for maintaining a low rate of
of CO2 leaking.
Besides for the cost of plants and infrastructures an
increase of expences of 15% is predicted.
In conclusion it appears to be a promising option with
uncertainties in his :
technical and
economical
ASPECTS.
Renewable
The total rate (TW) is shared between different categories:
-hydroelectric
0.3
pv=1.5
-geothermal
0.03
pv=12
-eolic
0.074
pv=7
-biomass
1.3
(+)
-solar
0.03
pv= 600
(+) due to the low efficiency of photosynthesis about 17%
of the of the terrestrial area land is required to produce
10TW.
Solar energy appears to be the only source able to supply
10-20 TW carbon-free power needed at 2050.
Fuel
Light
Electricity
Fuels
Electricity
CO
O2
2
H
2
e
e
Sugar
sc
H2O
M
sc
M
H 2O
O
2
Photosynthesis
Semiconductor/Liquid
Junctions
conversion strategies
Photovoltaics
What is the area needed
to generate the required
power?
-The full energy consumed in the world can be
produced in a tropical land with a squared area
with a side of 500 Km .
-The present energy employed in Italy can be
produced in a land area with a side of 60 Km
-It is sufficient to cover about 0.17 % of the
territory.
Solar is expensive
Typical levelized cost by source
(US cents/kWh)
50
25-50
40
Solar’s typical range of 25-50 cents/kWh is
much higher than other sources
30
20
10
2-4
2-6
2-7
4-6
6-8
0
Solar
C oal
Nuclear
Gas
Wind
Oil
It competes with grid price not generator cost
Average residential grid price
(US cents/kWh)
Japan
I taly
Germany
UK
US
South Korea
I ndia
C hina
25
Much easier to
compete with
grid price than
generation cost.
18
17
13
9
7
4
4
0
10
20
30
Market share by technology
A mo rphus silico n
a- Si
5%
5%
Ribbo n/sheet
Ribbon Si
crystalline*
4%
M o no crystalline*
33%
Other
2%
Silicon technology dominates the market:
93% for crystalline Si (single-, multi-, poly-,
nano-)
other 2%
4%
Single Si
33%
Poly Si
56%
10
Market share for Si and thin film
technologies were continuously decreasing
during last 10 years
P o ly crystalline*
56%
* C r y st a l l i n e t e c h n o l o g i e s. M o n o c r y st a l l i n e i s p u r e r t h a n p o l y c r y st a l l i n e a n d h a s h i g h e r e f f i c i e n c y
b u t h i g h e r c o st .
Prices and predictions
of photovoltaic market
Many different technologies on the market
rushing for high efficiency & low costs
Module efficiency
HIT heterojunction
intrinsic thin film
Lab scale Max efficiency
Shockley-Queisser analysis (1961)
It is based on four assumptions:
1- single p-n junction
2- one electron-hole pair excited for incoming photon
3- thermal relaxation of the electron-hole pair energy in
excess of the bandgap
4- illumination with unconcentrated sunlight
Maximum yield of 31% is obtained.
C
S-Q limit can be exceeded by violating one
or more of its premises.
A- Intermediate-band solar cells
B- Quantum-well solar cellsl
C-Multiple junctions cells
Employment of organic materials
XSC : Exciton Solar Cells
LUMO=Lowest Unoccupied Molecular Orbital
HOMO=Highest Occupied Molecular Orbital
Unsaturated Molecoles and
fullerenes for :
- harvesting solar radiations
-to give rise to a fast charge
transfer
-to limit the return to the ground
state
Plastic Cells: Scale-up using Roll-to-Roll Techniques
Printed or coated inexpensively on
flexible materials using roll-to-roll
manufacturing
Can be produced with varying
degrees of translucency so that it is
customized for specific markets
Environmentally friendly
Easily scaled up
Utilizes wide spectrum of light
16
Solar electricity cost as a function of module efficiency .
I- Wafers of silicon.
II- Thin films of amorphous silicon , tellurides, selenides
III- Research goals: carrier multiplication, multiple junctions,
sun light concentration, new materials (organic).
Photoelectrochemistry
SC semiconductor (photocatode)
M metal (anode)
Water photodissociation occurs if
hν>2.97 eV
(Photo)chemical Water Splitting:
2 H2O → O2 + 2H+ + 2e- +H2
Silicon Si
Gallium Arsenide AgAs
Titanium Dioxide TiO2
Eg = 1,1 eV
Eg = 1,5 eV
Eg = 3,2 eV
TiO2 fulfils the requirement but it absorbs only the ultraviolet radiation,
that is only 3% of the available solar energy.
Operation principles of a dye-sensitized mesoporous
heterojunction solar cell. (Gratzel)
Gray dots : mesoscopic oxide particles covered with a
monolayer of dye.
The development of energetic technologies
arises new and stimulating challenges for
chemical sciences :
-Complex systems including many degrees of freedom
.What is the real cost of the silicon solar energy?
.How important will the burning of coal be to global
warming?
- Chemistry of small molecules, implied in:
. Atmospheric chemistry
. Combustion
.New fuel synthesis.
.Excitaction and transfer of electrons.
- Chemistry of CO2 involving:
.New applications on large scale processes
-Design of new catalytic systems , involved in
energy production, such as.
.Activation of methane to methanol
CH4 + (1/2)O2 → CH3OH
.Photoreduction of CO2 to methanol
CO2 + 6H+ +6e- → CH3OH
.Improvement of the slow catodic processes reactions
.Fuel cells operating with metanol
CH3OH + H2O → CO2 + 6H+ + 6e-
The discover of new catalytic systems opens
important perspective in the synthesis of new
fuels.
Methane
CH4
Existing routes via syngas
Prospective direct routes being
researched
CO+2H2
(Synthesis gas)
Methanol
Hydrogen
Syncrude
Fuels
Chemicals
Lubricants
Olefins
Refinery
products
Ammonia
Jet Fuel
Diesel
“Gas to hydrogen”
Naphta
“Gas to liquids”
Dimethhyether
(DME)
“Gas to chemicals”
A secure energy future depends on wether chemists will discover efficient
catalysts for the production of alternative fuels .
Photosynthesis
Two massive protein complexes split water and
carbon dioxide and forge new energy-storing
bonds in sugar molecules.
Photosyntesis has immense
appeal for the closed cycle
capture of energy from the
sun.
The prospect of non
biological photosyntesis ,
that is through bio-inspired
chemical reactions ,
deserves new research.
How to design photosyntetic systems with artificial reaction
centers? Biominspired approach (BP)
-Chemical Antenna for harvesting solar
energy
-Chemical Structure able to transfer the
excited electron at fast speed.(0,1-1 ns)
photosyntesis
ET
BP
Gas-solid (PV)
interfaces
Relevance of electron transfer
processes ET
Liquid-solid
Syntetic Biology
Interdisciplinary approach including physics,chemistry
,biology and engineering, aimed to design and build
simplified biological catalytic systems with high efficiency.
In nature the metabolic pathways are connected in
complicated networks that have evolved for organisms
survival and reproduction and not for fuel production. The
relevant steps might be isolated and connected directly to
produce fuels such as hydrogen, methane and alcohols.
Post petroleum economy.
Craig Venter : Science on line, july 2007
The genome of one bacterium has been
succesfully replaced with that of a different
bacterium.
Then synthetic biology seems to make possible new cell
functions by fusing existing genomes.
Fall out on energy problems:
To develop an anaerobic species that will
digest cellulose into ethanol , thus generating a
fuel from biomass.
Though it be honest, it is never good to bring bad
news. (Shakespeare)
From the analysis of the carbon free options it comes out that:
-Fossil fuels are penalized by carbon dioxide sequestration
-Nuclear fission requires high investiments and
nevertheless it does not yet represent an alternative to fossil
fuels, unless new technological breakthrogh will emerge
-Eolic, geothermic and biomass energies can only give
an integrating support to the wide incoming energy
requirements
-Solar energy is promising but it requires a deep
transformation of the energy system
Stabilization triangle
divided in sectors each of one corresponding to an
advisable reduction of the emitted carbon.
Big importance is attributed to
the improvement of efficiency!
Conclusions
External limitations on carbon dioxide emissions imply the
adoption of precautions that will be introduced
through the adoption at local level of a mix of
different carbon free technologies in a mutual
integrated system ( energy saving, increase in
the employment of natural gas instead of
carbon, increase of renewable sources, nuclear,
…..)
THE END
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