SYNTHESIS OF AMORPHOUS

SILICON NANOPARTICLES

FROM AGRICULTURAL

WASTES FOR SOLAR

APPLICATIONS – A REVIEWS. B. Hassan, J. A. Adebisi, O. A. Ojo and J. O. Agunsoye

INTRODUCTION Energy generation and supply are problems that attract attention of all

nations because human welfare in modern life is closely related to the

amount and quality of energy utilized.

There has been a lot of projections on the nature and quantity of energy

that will be required in the next decades.

Institutions such as the International Energy Agency (IEA), the U.S. Energy

Information Administration (EIA), and the European Environment

Agency record and publish energy data periodically.

These data help in the understanding and revealing of the World Energy

Consumption systemic trends and patterns, which could help frame current

energy issues and encourage movement towards collectively useful

solutions.

The International Energy Agency has projected that energy demands willcontinue to increase until 2030.

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World* total primary energy supply by fuel

71,013 TWh 155,505 TWh

*World includes international aviation and international marine bunkers;** Peat and oil shale are aggregated with coal; and

***Includes geothermal, solar, wind, heat, etc.IEA, (2014). Key World Energy Statistics.

3

World total primary energy supply by region

71,013 TWh 155,505 TWh

*Asia excludes China.** Includes international aviation and international marine bunkers.

OECD: Organisation for Economic Co-operation and DevelopmentIEA, (2014). Key World Energy Statistics.

4

World electricity generation (TWh)

IEA, (2014). Key World Energy Statistics.

5

Electricity generation in Africa (TWh)

IEA, (2014). Key World Energy Statistics.

6

Electricity production to include Nigeria (kWh)

Index-Mundi. Electricity production (kWh). 2014 [cited 2014 12/11/2014]; Available from: http://www.indexmundi.com/facts/indicators/EG.ELC.PROD.KH/compare?country=ng#country=dz:eg:ng:za.

7

Population and electricity consumption per

capita for selected Africa countries

Extracted form: BP. Statistical Review of World Energy 2014.

PRB. Population Mid-2014.

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Renewables energy consumption - Solar (TWh)

IEA, (2014). Key World Energy Statistics.

9

What could be done in Nigeria? In 1998, Aduroja et al. reviewed the potential of photovoltaic

system in Nigeria.

In 2005, An electricity reform was suggested by Ikeme and

Ebohon that include increasing efficiency and share of

renewables in energy generation, as well as minimising

environmental damage.

In 2008, Akin Iwayemi suggested that one of the basic factors in

securing the electricity future in Nigeria is the energy mix (crude

oil, natural gas, coal, hydro, solar, wind and biomass) over the

next several decades.

In 2012, Oji et al. presented the viabilities for power generation

in Nigeria by the utilization of the sun’s energy through solar-

thermal or photovoltaic technologies.

There are several researches that has been done that focused

on how to solve the problems in this sector.

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Renewable energy One of the recurring suggestion here is the solar photovoltaics

technologies.

Solar photovoltaic (PV) energy has been seen as an elegant and

effective renewable energy resource that has proven to be a

promising candidate for provision of clean and sustainable power.

A solar photovoltaic (PV) module works by converting solar

radiation directly into electricity, using semiconductor technology.

From researches, it was observed that Nigeria could generate about

600,000 MW of electricity by deploying solar photovoltaic panels of

only 5% efficiency from just 1% of her land mass.

In the first quarter of 2014, Federal government of Nigeria planned

to fully harness the solar energy potential of the country through the

use of solar cells.

This has shown positive results in many countries like Turkey, EU

member states, India, Brazil, Algeria, etc.

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What do we have? The energy available in the

sun is more than 10,000 times

that required on the planet.

It is the cheapest form of

energy in areas where its

reception is high.

It costs nothing but space and

gadgets required to tap into it.

The average radiation in

tropical and sub-tropical

regions located in developing

countries can be compared

to that of annual global

radiation of about 1600 – 2200

kWh/m2.

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EIA, (2011). World map of solar resources. US Energy Information Administration.

13

http://commons.wikimedia.org/wiki/Fil

e:Solar_panels_on_house_roof.jpghttp://en.wikipedia.org/wiki/

File:Nellis_AFB_Solar_panels.j

pg

http://en.wikipedia.org/wiki/Solar

_power_in_Africa#mediaviewer/Fi

le:SolarGIS-Solar-map-Africa-and-

Middle-East-en.png

http://www.victor.sa.gov.au/page.aspx?u=

822

http://wordlesstech.com/wp-

content/uploads/2011/05/Solar-

panels-in-France.jpg

http://wordlesstech.com/2013/

11/19/kyocera-mega-solar-

power-plant/

http://ts2.mm.bing.net/th?id=HN.607988316

580678329&pid=15.1&P=0http://ts2.mm.bing.net/th?id=HN.60

8028010674719873&pid=15.1&P=0

http://ts4.mm.bing.net/th?id=HN.608043064

528995095&pid=15.1&P=0

Feasibility of achieving the suggestions

Focus of this paper Is there a way of harnessing the solar energy with our local

materials?

Are there agricultural wastes that could be used?

Burning of wastes increases the amount of greenhouse gas emission.

Improve the economic status of the farmers.

Are these materials in enormous production?

Will their conversion be economical and environmentally

friendly?

What are the researches that has been done using these

methods?

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Cassava peels15

Nigeria is the largest cassava producing country in the world with a tonnage of

about 30 million tonnes as at 2002.

Cassava peels can represent 5 to 15% of the root which invariably means 4.5

million tonnes of cassava peel waste could be produced.

Mostly in Nigeria, they are used for raising goats.

The part that is needed in the peel is not what the goats need.

PHOTOVOLTAIC MATERIALS

Silicon solar cells make up 95% of solar cells and are the most developed and

commercialized types of photovoltaic cells.

In terms of purity level, silicon could be classified in priority as either

semiconductor/electronic grade (EG-Si),

solar grade (SOG-Si) or

metallurgical grade (SoG-Si).

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PV materials

Crystalline silicon

86% market share

Thin film

Organic/polymer

Hybrid PV polymer

Dye-sensitized

CdS/CdTe

Amorphous silicon

13% market share

CIS/CIGS

Single junction

Double junction

Triple junction

Mono-Crystalline

Poly-Crystalline

GaAs

SoG-Si production/MG-Si purification The Siemens based processes (thermal decomposition of silane and/or H2

reduction of silicon halides).𝑆𝑖𝐻4 𝑔 → 𝑆𝑖(𝑠,𝑝𝑜𝑤𝑑𝑒𝑟) + 2𝐻2(𝑔)

𝑆𝑖𝐵𝑟4(𝑝𝑢𝑟𝑖𝑓𝑖𝑒𝑑) + 2𝐻2(𝑔) → 𝑆𝑖(𝑠)(𝑝𝑢𝑟𝑒) + 4𝐻𝐵𝑟

Metallothermic reduction of Si halide compounds.𝑆𝑖𝐹4(𝑔) + 4𝑁𝑎(𝑙) → 𝑆𝑖(𝑠,𝑝𝑜𝑤𝑑𝑒𝑟) + 4𝑁𝑎𝐹(𝑠)

Reduction of silica. 𝑆𝑖𝑂2(𝑠) + 2𝐶(𝑠) → 𝑆𝑖(𝑠) + 2𝐶𝑂(𝑔)

𝑆𝑖𝑂2(𝑠) + 2𝑀𝑔(𝑠) → 𝑆𝑖(𝑠) + 2𝑀𝑔𝑂(𝑠)

Fluoride processes for the preparation of high purity silicon.𝐻2𝑆𝑖𝐹6 + 2𝑁𝑎𝐹 → 2𝐻𝐹 + 𝑁𝑎2𝑆𝑖𝐹6

𝑁𝑎2𝑆𝑖𝐹6→Δ2𝑁𝑎𝐹 + 𝑆𝑖𝐹4(𝑔)

Upgrading MG-Si.

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The make of solar cells

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It should be noted here that a-Si take 8% production share, it has someadvantages.

Amorphous silicon solar cells can be fabricated on large area and on

different substrates without raw material problem which makes them suitable

for low-cost and mass production.

SYNTHESIS OF NANOPARTICLESNo

Starting

material(s)Reagents/other materials Procedural highlights Product(s)

Particle size

(nm)

1

Corn tissues

(leaves, roots,

stalks, silks, and

husks)

HCl, ethanol solution of

tetrabutyl titanate

Acid pre-treatment, in-situ growth

(impregnation), calcination,

crystallization

Max. Temp. 550 oC

porous

TiO2–SiO2

composites

13.8 – 20.3

2 Rice husk (RH)

HCl, H2SO4, HNO3,

CH3COOH, NaOH, CaO,

NH4OH, EDTA, KOH

Acid pre-treatment, combustion,

leaching, pyrolysis, sol-gel

Max. Temp. 500 °C, 700 °C, 1,000 °C

Silica 6

3RH (from 2

different sources)

acetic, citric and phosphoric

acids

Leaching, calcination

Max. Temp. 650 oCSilica 181.2 – 294.7

4 Corn hob

NaOH, HCl, cetyltrimethyl

ammonium chloride

(CTMAC), ammonia

Pyrolysis, sol-gel, calcination

Max. Temp. 700 oCSilica 305

5

Rice, sylvan

horsetail, scouring

horsetail and larch

needles

HCl, Mg, H2SO4, HF

Hydrolysis, calcination, metallothermic

reduction

Max. Temp. 700 oC

Amorphous

silica50 – 200

6 sugarcane bagasseH2SO4, benzene, methanol,

acidified NaCl, KOH,

Pulverizing, isolation, acid-hydrolysis

Max. Temp. 105 ◦CCellulose 20-60

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PRODUCTION OF SILICON Four research works were obtained from previous works.

Banerjee et al. (1982): RH, HCl, HF, H2SO4, Mg, MgO. amorphous silica, silicon.

Mishra et al. (1985): RH, HCl, HNO3, HF, Ca. amorphous silica, 99.9% silicon.

Ikram and Akhter (1988): RH, HCl, Mg. amorphous silica, 99.95% silicon.

Larbi et al. (2012): RHA, HCl, CH3COOH, PVA, Mg. amorphous silica, 99.3% silicon.

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Pre-treatment

•Washing/rinsing

•Acid leaching

• (RH, HCl, distilled water)

Silica Production

• Burning in air

•Acid leaching (may involve several stages)

• (RHA, HCl, HF, CH3COOH, H2SO4, HNO3)

Silicon production

•Metallothermicreduction

•Acid leaching (may involve several stages)

• (Silica, Mg/Ca,HCl, HF, CH3COOH, H2SO4, HNO3)

PURIFICATION OF SILICON This is an essential step in industrial SoG-Si production.

It has been employed for upgrading MG-Si to SoG-Si at

lower cost.

The various methods could be grouped as follows:

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Leaching

Ladle treatment (slagging, gas blowing)

Solidification methods

Crystallization methods

Solvent refining

Ion exchange

Vacuum methods

CONCLUSION

Energy generation and supply are still challenges in Nigeria.

Waste generation and management in the country constitute

to the environmental pollution and their conversion to wealth is

still low.

Renewable energy has been seen as the solution to energy

challenges and climate change.

Conversion of waste to wealth could ameliorate our

unemployment challenges and reduce environmental

problems.

This review has been writing to convert some agricultural

wastes to renewable energy sources in the country.

The silicon grade that is aimed will be focused in solar energy

application.

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Await your contributions

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